Class 10 Physics

PSEB Class 10 Physics Solutions For Chapter 1 Light-Reflection And Refraction

Light

Light is the form of energy that enables us to see. An object reflects light that falls on it. We are able to see the object when this reflected light is received by our eyes.

Properties Of Light

1. Light travels in a straight line. Due to this, light casts a shadow of the object placed in its path.
2. Light is an electromagnetic wave. It does not require any medium to travel.
3. The speed of light is maximum in a vacuum. It is 3×108 ms^-1.
4. Light has a dual nature, i.e., particle as well as wave nature.
5. When light falls on an object, one or more of reflection, refraction, or absorption may happen.

Types Of Materials Based On Absorption Of Light

Three types of materials based on absorption of light are Transparent, Translucent, and Opaque.

PSEB Class 10 Physics Chapter 1 Light-Reflection And Refraction

Reflection Of Light

The phenomenon of bouncing back of light into the same medium, when it strikes a polished or smooth surface, is called reflection.

Incident Ray = Light ray which falls on the polished or smooth surface

Reflected ray = Light ray that gets bounced back from the polished or smooth surface.

Laws Of Reflection

Applicable to all types of reflecting surfaces, including spherical surfaces

1. Angle of Incidence (∠i) = Angle of Reflection (∠r)
2. Incident Ray, Normal to the angle of incidence, and Reflected Ray all lie in the same plane.

Image– It is the point at which two rays actually meet or appear to meet. An image can be of two types: Real or Virtual.

Characteristics Of the Image Formed By a Plane Mirror

1. The image formed is Virtual- formed behind the mirror.
2. Size of image = Size of Object
3. Distance between mirror and object = Distance between mirror and image
4. Laterally inverted- means the left side of the object appears right and the right side of the object appears left.

Spherical Mirrors

Mirrors whose reflecting surface forms part of the sphere are called spherical mirrors. They are of two types – Concave mirrors and Convex mirrors, as shown below:

Some Important Terms Used In Context To Spherical Mirrors

Pole (P) – Centre of the spherical mirror.

Centre of Curvature (C) – The centre of the hollow glass sphere of which the spherical mirror was a part.

Principal Axis – Line joining the pole (P) and centre of curvature (C).

Radius of Curvature (R) – Distance between pole (P) and centre of curvature (C).

Principal Focus (F) – Point on the principal axis where all rays actually meet or appear to meet.

Focal Length (f) – Distance between pole (P) and principal focus (F).

Aperture (MN) – Effective diameter of the spherical mirror.

Relationship Between Focal Length (f) And Radius Of Curvature (R)

Focal Length (f) = Radius of Curvature (R)/2

Rules For Making Ray Diagrams For Spehrical Mirrors

Simple Trick To Remember Image Formation By Concave Mirror

Step 1: Write position of object starting from infinity till between F and P.

Step 2: Write numbers 5, 4, 3, 2, 1 to all positions of object, and numbers 1, 2, 3, 4, 5 to all positions of image. (Note that numbers given to positions of objects are 5-1 and those given to image positions are 1-5. This is important point to be remembered).

Step 3: Comparing the numbers will give us the size of image, For Examle Since1 is very less than 5, size of image will be highly diminished, 2 is less than 4, therefore image will be diminished, and so on (as given in table below).

Note:

• For object position numbers 5, 4, 3, 2 and 1, image will be real and inverted.
• Last position of object is an exception- in this case image will be virtual and erect.

image

Simple Trick To Remember Image Formation By Convex Mirror

Important Note: Image formed by convex mirror is always virtual, erect and small in size.

Uses Of Concave Mirrors

1. Used in torches, search-lights and vehicles headlights to get powerful parallel beams of light as shown in diagram:

2. Used as shaving mirrors to see a larger image of the face, and also used by dentists to see large images of the teeth of patients. For this, the object has to be placed between pole and focus, as shown in figure:

PSEB Class 10 Physics Solutions Chapter 1

3. Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.

4. Used as satellite dish TV antennas as shown in figure:

Uses Of Convex Mirrors

1. Used as rear-view (wing) mirrors in vehicles because:

• They always give an erect, though diminished, image.
• They have a wider field of view as they are curved outwards, as shown in figure.

2. Used at blind turns and points of merging traffic to give view of traffic from both sides.

3. Used in shops as security mirror.

New Cartesian Sign Conventions – For Reflection By Spherical Mirrors

In the New Cartesian Sign Convention,

• Pole (P) of the mirror is taken as the origin.
• Principal axis of the mirror is taken as the x-axis of the coordinate system.
• The New Cartesian Sign Convention are summarized in the figure provided below (For details, please refer points 1-5 given after the figure):

1. Object is always placed to the left of the mirror, i.e, light from the object falls on the mirror from the left-hand side.
2. All distances parallel to the principal axis are measured from the pole of the mirror.
3. All the distances measured to the right of the origin (along + x-axis) are taken as positive while those measured to the left of the origin (along- x-axis) are taken as negative.
4. Distances measured perpendicular to and above the principal axis (along + y-axis) are taken as positive.
5. Distances measured perpendicular to and below the principal axis (along -y-axis) are taken as negative.

Conclusions From New Cartesian Sign Conventions For Spherical Mirrors

Distance of Object from Mirror (u) = Always Negative

Focal length of Concave Mirror (f) = Negative

Focal length of Convex Mirror (f) = Positive

Mirror Formula

It gives the relation between distance of object, distance of image and focal length of the mirror. According to mirror formula

∴ \(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)

Where, u = distance of object from pole, v = distance of image from pole, and f = focal length of mirror.

Mirror formula is valid for plane mirrors as well as spherical mirrors for all positions of the object.

Important Note: For solving numerical problems, New Cartesian Sign Conventions must be considered while substituting values for u. v, f (or R. if focal length is calculated using relation f = R/2) in the mirror formula.

Magnification Of Spherical Mirrors

Magnification (m) is defined as the ratio of height of image to the height of object.

∴ \(m=\frac{\text { Height of image }}{\text { Height of object }}=\frac{h_i}{h_o}=-\frac{v}{u}\)

Simple Trick To Find The Type Or Size Of Image From Value Of Magnification

Important Note:

• Magnification of convex mirror is always negative.
• Magnification of concave mirror can be positive or negative depending on the position of the object.

Refraction Of Light

The phenomenon of bending of light when it enters obliquely from one transparent medium into another is called refraction of light. Refraction occurs due to change in speed of light in different media.

Light-Reflection And Refraction PSEB Class 10 Notes

Bending Of Light In Refraction

1. If a ray of light passes from a material in which it travels fast (rarer medium) into a material in which it travels slower (denser medium), then the light ray will bend towards the normal, i.e,

2. If a ray of light passes from a material in which it travels slow (denser medium) into a material in which it travels faster (rarer medium), then the light ray will bend away from the normal.

Simple Trick To Remember The Direction Of Bending Of Light In Refraction

Direction of bending of light in refraction can be easily remembered using the mnemonic “FAST SOFA”

3. Extent of bending of incident ray depends upon difference in refractive index between the two medium through which the ray is passing.

4. Emergent Ray is parallel to Incident Ray because the extent of bending of ray of light at the opposite parallel faces of the second medium (glass in this case) is equal and opposite as shown:

5. Perpendicular distance between the incident ray and the emergent ray is called lateral displacement or lateral shift (d). It depends upon:

• Thickness of the glass slab
• Refractive index of the glass slab

Refractive Index (n)

It is defined as the ratio of velocity of light in a given pair of media, i.e.,

∴ \(n=\frac{\text { Velocity of light in medium } 1}{\text { Velocity of light in medium } 2}\)

Points To Remember About Refractive Index

1. Refractive index has no units because it is a ratio.
2. Refractive index does not depend on the physical density of the medium, For Example kerosene having higher refractive index, is optically denser than water, although its mass density is less than water.
3. Refractive index of water, n_water= 1.33, and refractive index of air, n_air = 1. This means that the ratio of the speed of light in air and the speed of light in water is equal to 1.33.
4. Refractive index of diamond is highest till date. Its value is 2.42. This means speed of light in diamond is 1/ 2.42 times less than the speed of light in air or vacuum.
5. n₂₁ means refractive index of 2^nd medium with respect to 1^st medium, whereas n₂₁ means refractive index of 1^st medium with respect to 2^nd medium, i.e.,

∴ \(n_{21}=\frac{V_1}{V_2} \quad \text { whereas } \quad n_{12}=\frac{V_2}{V_1}\)

Absolute Refractive Index

It is the ratio of the speed of light in vacuum to the speed of light in the given medium, i.e.,

∴ \(n=\frac{c}{v}\)

where c = 3 x 10⁸ ms^-1

Important Note: Absolute refractive index can never be less than 1 because the speed of light in any medium is always less than that in a vacuum.

Optically Rarer And Optically Denser Medium

Optically Rarer Medium – Medium with a lower value of refractive index

Optically Denser Medium – Medium with a higher value of refractive index

For Example – Out of Air and Glass, glass is denser medium while air is rarer medium.

PSEB Class 10 Physics Important Questions Chapter 1

Laws Of Refraction

The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.

The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. This law is also known as Snell’s law of refraction. Thus, according to Snell’s law,

∴ \(\frac{\sin i}{\sin r}=\text { constant }\)

The constant value is called the refractive index of the 2^nd medium with respect to the 1^st medium.

Snell’s law is true for 0 < i < 90°, where “i” is the angle of incidence.

Some Common Examples Of Refraction

1. The bottom of swimming pool appears higher due to refraction of light on entering water through air.
2. A pencil partially immersed in water appears to be bent at the interface of air and water.
3. When a thick glass slab is placed over some printed matter, the letters appear raised.
4. Lemons placed in a glass tumbler appear bigger.

Spherical Lens – A transparent material bound by two surfaces, of which one or both surfaces are spherical, forms a lens.

Four Types Of Spherical Lens

Difference Between Concave Lens And Convex Lens

Some Important Terms About Lens

Since both convex and concave lens have two spherical surfaces, it has two centres of curvature and two principal focus.

Centre of Curvature (C)– It is the centre of the sphere of which the lens forms a part. Because a lens has two spherical surfaces, it has two centres of curvature (C₁ and C₂ as shown in above figures).

Radius of Curvature (R)– It is the radius of the sphere of which the spherical surface of lens forms a part. R₁ and R₂ are radii of curvature in above figures.

Principal Axis (C₁C₂ – It is the line passing through the two centres of curvature (C₁ and C₂) of the lens.

Optical Centre (O) – If a ray of light is incident on a lens such that after refraction through the lens the emergent ray is parallel to the incident ray, then the point at which the refracted ray intersects, the principal axis is called the optical centre of the lens.

Note: Optical centre of lens coincides with the geometric centre of the lens when the radii of curvature of the two surfaces are equal.

Aperture– The diameter of the circular boundary of the lens is called its aperture.

Principal Focus (F)– It is the point through which a parallel light after refraction passes through in the case of a convex lens and appears to pass through in the case of a concave lens. A lens has two focal points, because a lens has two refracting surfaces.

Focal Length (f)– It is the distance of the principal focus from the optical centre of a lens.

1. First Principal Focus (F1) and First Focal Length (f) – It is a fixed point on the principal axis such that rays starting from this point (in convex lens) or appearing to go towards this point (concave lens), after refraction through the lens, become parallel to the principal axis.

2. Second principal focus (F2) and second focal length (f’)– It is a fixed point on the principal axis such that the light ravs incident parallel to the principal axis, after refraction through the lens, either converge to this point (in convex lens) or appear to diverge from this point (in concave lens).

Important Note: If the medium on both sides of a lens is same, then first and second focal lengths are equal, i.e, f = f.

Rules For Image Formation By Lens

Simple Trick To Remember Image Formation By Convex Lens

Step 1: Write position of object starting from infinity till between F and P.

Step 2: Write numbers 1-6 to all positions of object, and numbers 5-1 to all positions of image as shown in figure.

Step 3: Comparing the numbers will give us the size of image, For Example. Since 1 is very less than 5, size of image will be highly diminished, 2 is less than 4, therefore image will be diminished, and so on (as given in table below).

Note:

• For object position numbers 5-1, image will be real and inverted.
• Last position of object is an exception- in this case image will be virtual and erect.

This trick will become clear from illustration given below:

Simple Trick To Remember Image Formation By Concave Lens

Important Note: Image formed by Concave Lens is always Virtual. Erect and Small in size.

Lens Formula – It gives the relation between distance of object (u), distance of image (v) and focal length (f) for a lens. According to lens formula,

∴ \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

Note: Lens formula is valid in all situations for all types of spherical lens.

Magnification Of Lens – It is defined as the ratio of the height of an image (hi) to the height of an object (h0). It is also written as ratio of distance of image from optical centre and distance of object from optical centre, i.e,

∴ \(m=\frac{h_i}{h_o}=\frac{V}{u}\)

Simple Trick To Find The Type or Size Of Image From Value Of Magnification

Power Of Lens (P)– Power (P) of a lens gives the degree of convergence or divergence of light rays achieved by a lens. Power of lens is the reciprocal of its focal length.

∴ \(\text { Power }=\frac{1}{\text { focal length (in meter) }} \mathrm{P}=\frac{1}{f}\)

SI unit of power of a lens is ‘dioptre’ (D). 1 dioptre is the power of a lens having focal length of lm, i.e., ID = lm-1.

PSEB Class 10 Science Chapter 1 Solutions

Points To Remember About Power Of Lens

1. Power of a Convex Lens = Always positive
2. Power of Concave Lens = Always Negative.
3. Opticians use of the term power of lens instead of their focal lengths.
4. In many optical instruments, number of lenses is combined to increase the magnification and sharpness of the image. In such instruments, the net power (P) of the lenses is given by the algebraic sum of the individual powers PI, P2, P3, … i.e, P = PI + P2 + P3 + …..

Chapter 1 Light-Reflection And Refraction Reason – Assertion Questions And Answers

The following questions consist of two statements- Assertion (A) and Reason (R). Answer these questionsby  selecting the appropriate option given below:

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Question 1. Assertion (A): Large concave mirrors are used to concentrate sunlight to produce heat in solar cookers.

Reason (R): Concave mirror converges the light rays falling on it to a point.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Question 2. Assertion (A): The focal length of the mirror is f and the distance of the object from the focus is u. The magnification of the mirror is f/u.

Reason (R): Magnification = + Size of image/ Size of object

Answer: 3. A is true but R is false.

Question 3. Assertion (A): For observing traffic at back, the driver mirror is a convex mirror.

Reason (R): A convex mirror has a much larger field of view than a plane mirror.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Question 4. Assertion (A): Higher is the refractive index of a medium or denser the medium, lesser if the velocity of light in that medium.

Reason (R): Refractive index is inversely proportional to velocity.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Question 5. Assertion: The image formed by a concave mirror is certainly real if the object is virtual.

Reason: The image formed by a concave mirror is certainly virtual if the object is real.

Answer: 3. A is true but R is false.

Question 6. Assertion: The bending of a stick appears to take place by different amounts in different liquids.

Reason: Light is refracted in different media by different amount.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Question 7. Assertion: A stick partly immersed in water appears to be bent.

Reason: Refraction of light when it passes from water into air.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Question 8. Assertion: Refractive index of glass with respect to air is different for red light and violet light.

Reason: Refractive index of a pair of media depends on wavelength of light used.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Question 9. Assertion: When objects are observed through hot air, they appear to be moving slightly.

Reason: The hotter air is optically denser and the colder air is optically rarer.

Answer: 3. A is true but R is false.

Chapter 1 Light-Reflection And Refraction Case Or Source Based Questions And Answers

Question 1. Nalini, a young student, was trying to demonstrate some properties of light in her Science project work. She kept X inside the box (as shown in the figure) and with the help of a laser pointer made light rays pass through the holes on one side of the box. She had a small butterpaper screen to see the spots of light being cast as they emerged.

1) What could be the ‘X’ that she placed inside the box to make the rays behave as shown?

1. A converging lens
2. A parallel-sided glass block
3. A plane mirror
4. A triangular prism

Answer: 2. A parallel-sided glass block

2) She measured the angles of incidence for both the rays on the left side of the box to be 48.60. She knew the refractive index of the material ‘X’ inside the box was 1.5. What will be the approximate value of angle of refraction?

1. 450
2. 400
3. 300
4. 600 (use the value: sin 48.60 = 0.75)

Answer: 3. 300

3) Her friend noted the following observations from this demonstration:

1. Glass is optically rarer than air.
2. Air and glass allow light to pass through them with the same velocity.
3. Air is optically rarer than glass.
4. Speed of light through a denser medium is faster than that of a rarer medium.

The ratio: sin of angle of incidence in the first medium to the ratio of sin of angle of refraction in the second medium, gives the refractive index of the second material with respect to the first one.

Which one of the combination of the above statements given below is correct.

2, 4 and 5 are correct.

3 and 4 are correct.

1, 4 and 5 are correct.

3 and 5 are correct.

Answer: 4. 3 and 5 are correct.

4) If the object inside the box was made of a material with a refractive index less than 1.5 then the

1. Lateral shift of the rays would have been less.
2. Lateral shift of the rays would have been more.
3. Lateral shift of the rays would remain the same as before.
4. There is not enough information to comment on any of the above statements.

Answer: 1. Lateral shift of the rays would have been less.

Question 2. A concave mirror has focal length 10 cm. Answer the questions using the following table:

1) If object size is 2 cm, what would be the size of the image in case A?

1. 2 cm
2. 10 cm
3. 4 cm
4. Less than 2 cm

Answer: 1. 2 cm

2) Nature of the image when u = -15 cm

1. Virtual and inverted
2. Real and erect
3. Virtual and erect
4. Real and inverted

Answer: 4. Real and inverted

3) Nature of the image in case (D)

1. Virtual and inverted
2. Real and erect
3. Virtual and erect
4. Real and inverted

Answer: 3. Virtual and erect

4) Position of the image in case (C)

1. At centre of curvature
2. At focus
3. At infinity
4. Between focus and centre of curvature

Answer: 2. At focus

5) What is the distance at which the centre of curvature located?

1. 5 cm
2. 10 cm
3. 20 cm
4. 15 cm

Answer: 3. 20 cm

Question 3. An object is placed at the following distances from a convex lens of focal length 15 cm:

1. 35 cm
2. 30 cm
3. 20 cm
4. 10 cm.

Which position of the object will produce:

1) A magnified real image?

1. 35 cm
2. 30 cm
3. 20 cm
4. 10 cm

Answer: 3. 20 cm

Here, f = 15cm and 2f = 30cm

Because a magnified real image is formed when the object is placed between f and 2f.

2) A magnified virtual image?

1. 35 cm
2. 30 cm
3. 20 cm
4. 10 cm

Answer: 4. 10 cm

Because a magnified virtual image is formed when the object is placed between f and the lens.

3) A diminished real image?

1. 35 cm
2. 30 cm
3. 20 cm
4. 10 cm

Answer: 1. 35 cm

Because a diminished real image is formed when the object is placed beyond 2f.

4) An image of same size as the object?

1. 35 cm
2. 30 cm
3. 20 cm
4. 10 cm

Answer: 2. 30 cm

Because an image of same size as the object is formed when the object is placed at 2f.

5) At what distance will the image be formed when an object is placed at 30 cm for this converging lens?

1. 10 cm
2. 20 cm
3. 25 cm
4. 30 cm

Answer: 4. 30 cm

When an object is placed at 2F of converging lens the image will be formed at 2F’ at right side of lens and image formed is real, inverted and of same size.

Question 4. The figure given below illustrates the ray diagram for the formation of image by a concave mirror. The position of the is beyond the centre of the curvature of the concave mirror. On basis of the given figure answer the questions given below.

1) If focal length of the concave mirror is 10 cm, the image formed will be at a distance _______.

1. Between 10 cm and 15 cm
2. Between 10 cm and 20 cm
3. Beyond 20 cm
4. At 20 cm

Answer: 2. Between 10 cm and 20 cm

Explanation: The focal length of the mirror is 10 cm. This mean, the radius of curvature is 20 cm. From figure, it is clear that the image is formed between the focus and centre of curvature. Thus, the image is formed between 10 cm and 20 cm.

2) In case of concave mirror, the image distance from the pole of the mirror is

1. Always positive
2. Always negative
3. Negative or positive depending upon the position of the object
4. None of these

Answer: 3. Negative or positive depending upon the position of the object.

3) If the size of the object in the given figure is 5 cm and the magnification produced is – 0.5. The size of the image is

1. -2.5 cm
2. -0.1 cm
3. 2.5 cm
4. 0.1 cm

Answer: 1. -2.5 cm

= h2/h1; h2 = (- 0.5 x 5)/ 10; h2 =- 2.5 cm

4) A negative sign in the magnification value indicate that the image is

1. Real and inverted
2. Real and erect
3. Virtual and erect
4. Virtual and inverted

Answer: 1. Real and inverted

5) If the value of magnification is greater than 1 then it indicates that the image formed is

1. Diminished
2. The same size as that of the object
3. Enlarged
4. Value of magnification cannot specify whether the image is diminished or magnified.

Answer: 3. Enlarged

Question 5. When a spherical mirror is held towards the sun and its sharp image is formed on a piece of carbon paper for some time, a hole is burnt in the carbon paper. Answer the following questions in reference to the above activity.

1) What is the nature of spherical mirror?

1. Convex mirror
2. Concave mirror
3. Plane mirror
4. Plano convex mirror

Answer: 2. Concave mirror

2) Why is a hole burnt in the carbon paper?

1. Sun rays are dispersed by the spherical mirror
2. The Sun’s heat rays are concentrated at the point of sun’s image
3. Sun rays get diverged after reflection from spherical mirror
4. Due to atmospheric refraction

Answer: 2. The Sun’s heat rays are concentrated at the point of sun’s image

3) At which point of the spherical mirror the carbon paper is placed?

1. Between pole and focus
2. Between centre of curvature and focus
3. Anywhere between infinity and focus
4. At focus

Answer: 4. At focus

4) What name is given to the distance between spherical mirror and carbon paper?

1. Image distance
2. Object distance
3. Focal length
4. Principal axis

Answer: 3. Focal length

5) For the above-mentioned spherical mirror, the image formed by it when the object is placed at its centre of curvature is

1. Twice the size of the object
2. Greater than size of object
3. Equal to the size of the object
4. Less than the size of the object

Answer: 3. Equal to the size of the object

PSEB Class 10 Biology Solutions For Chapter 4 Magnetic Effects Of Current

Background

Hans Christian Oersted discovered that electricity and magnetism are interrelated forces. Einstein’s “Theory Of Relativity” later proved that electricity are magnetism are two different aspects of one common phenomenon.

However, in practical terms, electric and magnetic forces behave quite differently – although electric forces are produced by electric charges either at rest or in motion, magnetic forces are produced only by moving charges, and act solely on charges in motion.

Magnet

A substance which can attract a piece of iron, cobalt, or nickel is called a magnet. The property by virtue of which a magnet attracts these substances is called magnetism. A magnet has two poles, viz. North Pole and South Pole as shown:

Magnetic Field

The region around a magnet where the effect of a magnet can be felt is called magnetic field. Magnetic field is a vector quantity, i.e., magnetic field has both direction and magnitude. It is created by an electric current or magnetic dipole.

Magnetic Field Lines

The lines along which the iron filings align themselves, when a bar magnet is brought near them, are called magnetic field lines.

Magnetic field lines are imaginary lines to visualize magnetic field, For Example. When we bring a bar magnet near iron filings, the iron fillings arrange themselves in a pattern as shown. This pattern of lines indicates the magnetic field lines around the bar magnet.

Electromagnetism

The branch of physics that studies the interactions between electric and magnetic fields is called electromagnetism.

Sign Conventions About Magnetic Field Lines

1. Magnetic field lines always begin from the N-pole of a magnet and end on the S-pole of the magnet.
2. Magnetic field lines form closed curves, i.e, inside the magnet they move from South pole to North pole.
3. Magnetic field lines never cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.
4. The strength of magnetic field is indicated bv the degree of closeness of the field lines. So, magnetic field is the strongest, where the field lines are closest together.

Factors On Which Magnetic Field Depends – Two factors determining amount of magnetic field (B) produced by a current carrying conductor are:

Magnetic field produced is directly proportional to current (I), i.e., B ∝ I

Magnetic field produced is inversely proportional to the radius (r) of the circular loop, i.e, B ∝ 1/r

PSEB Class 10 Physics Solutions Chapter 4

Right Hand Thumb Rule Or Maxwell’s Corkscrew Rule – It gives the direction of magnetic field lines in a current carrying conductor.

According to this rule, if we grasp (or hold) the current-carrying wire in our right hand so that our thumb points in the direction of current, then the direction in which our fingers encircle the wire will give the direction of magnetic field lines around the wire. This is shown in figure below:

From the above figure, one can easily deduce that if the direction of current in a conductor is reversed, the direction of magnetic field lines will also get reversed.

Maxwell’s Corkscrew Rule

If we consider ourselves driving a corkscrew in the direction of the current, then the direction of the rotation of the corkscrew is the direction of the magnetic field.

Magnetic Field Produced Due To Flow Of Current In A Straight Wire, A Circular Loop, And A Solenoid

1. Magnetic field due to a current through a straight wire – The amount of magnetic field produced is proportional to the current in the conductor. The direction of the current can be found using right-hand thumb rule.

2. Magnetic field due to a current through a circular loop – We know that the magnetic field produced by a current-carrying straight wire depends inversely on the distance (r) from it.

Therefore, the concentric circles representing the magnetic field around it would become larger and larger as we move away from the wire as shown in the figure.

Further, on reaching the centre of the circular loop, the arcs of these big circles will become almost straight and therefore, would appear as straight lines as shown in figure:

By applying the right hand thumb rule on the above current carrying wire, we can observe the following:

• Every section of the wire contributes to the magnetic field lines in the same direction within the loop.
• Direction of magnetic field at the centre of circular coil is perpendicular to the plane of the coil, i.e., along the axis of the coil.

3. Magnetic field due to solenoid – A solenoid is a long cylindrical coil of insulated copper wire having large number of circular turns as shown in figure:

A current carrying solenoid is called an electromagnet because when current is passed through a solenoid, magnetic field is created.

Magnetic field produced by a solenoid is similar to the magnetic field produced by a bar magnet. Due to the presence of turns in the solenoid, magnetic field inside the solenoid is in the form of parallel straight lines, and is the same at all points inside the solenoid as shown in figure.

Strength of magnetic field produced by a current carrying solenoid depends on following factors:

1. Number Of Turns In The Solenoid – Larger the number of turns in the solenoid, greater will be the magnetism produced.
2. Strength Of Current In The Solenoid– Larger the current passed through solenoid, stronger will be the magnetic field produced.
3. Nature of the core material – The use of soft iron rod as core in a solenoid produces the strongest magnetism.

Advantages of electromagnets (current carrying solenoid) over bar magnets

1. Unlike bar magnets, electromagnets can be switched on and switched off.
2. Magnetic field inside electromagnets can be increased by increasing the number of turns in the coil.

Force on a current carrying conductor in a magnetic field – So far we know that a current-carrying conductor produces a magnetic field around it, i.e, it behaves like a magnet and exerts a force when a magnet is placed in its magnetic field.

In addition to this, the magnetic field also exerts equal and opposite force on the currentcarrying conductor because when the two magnetic fields (i.e., magnetic field produced by the current-carrying conductor and magnetic field due to the nearby magnet) interact with eachother.

There exist attractive or repulsive forces between the two magnetic fields depending upon the direction of the external magnetic field and the direction of the current in the conductor.

The direction of force acting on the current carrying conductor can be determined using Fleming’s Left-Hand Rule.

According to Fleming’s Left Hand Rule, if the left hand is stretched in a way that the forefinger, the center finger, and the thumb are in mutually perpendicular directions.

Then the direction of the forefinger will give the direction of magnetic field, the direction of center finger will give the direction of electric current and the direction of thumb will give the direction of force acting on the conductor as shown:

Factors Affecting Direction Of Force In A Current Carrying Conductor

1. Direction of Current – If we change the direction of flow of current, the direction of force will change.
2. Direction of Magnetic Field– If we change the direction of poles of magnet, the direction of force will change.

Magnetic Effects Of Current PSEB Class 10 Notes

Factors Affecting Magnitude Of Force In A Current Carrying Conductor

1. Amount of current flowing through the conductor – More the amount of current flowing through the conductor, more will be the force.
2. Direction of Magnetic Field – Force acting on a current carrying conductor is highest when the direction of magnetic field is perpendicular to the direction of electric current.

Applications Of Magnetism In Real Life

1. MRI (Medical Resonance Imaging).
2. Magnetic Compass is used during hiking for finding the direction as it always points towards North-South direction.
3. Electric Motors – An electric motor is a rotating device that converts electrical energy to mechanical energy. Electric motors are used in hair dryers, electric razors, hair and beard trimmers, washing machines, etc.
4. An electric motor works on the principle of magnetic effects of current. An electric motor consists of a rectangular coil placed in a magnetic field. When current is passed through the coil, the coil rotates as a result of the forces acting on it.

Electromagnetic Induction – It is the process of using magnetic fields to produce voltage or current in a closed circuit.

Points To Remember About Electromagnetic Induction

1. Electromagnetic Induction was discovered by Michael Faraday.
2. Electromagnetic induction is a way of producing electrical current in a circuit by using only the force of a magnetic field, and not batteries.
3. Transformers and Generators work on the principle of electromagnetic induction.

Factors Affecting Electromagnetic Induction

1. Number of turns of wire in the coil – More the number of turns in the coil, more will be the voltage or current produced.
2. Increasing the speed of the relative motion between the coil and the magnet will increase the voltage or current produced.
3. Increasing the strength of the magnetic field – If the same coil of wire is moved at the same speed through a stronger magnetic field, more voltage or current will be produced.

Electric Generator – An electric generator, also called a dynamo, is a machine that converts mechanical energy into electricity for transmission and distribution over power lines.

Working Of An Electric Generator

An electric generator works on the principle of electromagnetic induction.

1. In an electric generator, a conductor coil, called armature (a copper coil tightly wound onto a metal core), connected to a shaft of a mechanical energy source (such as a motor) is rotated rapidly between the poles of a horseshoe-type magnet.
2. The energy to the mechanical energy source is provided by engines operating on fuels such as diesel, petrol, etc.

Fleming’s Right Hand Rule (For Generators)- It gives the direction of induced current when a conductor attached to a circuit moves in a magnetic field.

According to Fleming’s Right Hand Rule, if the forefinger indicates the direction of the magnetic field and the thumb shows the direction of motion of the conductor, then the middle finger will show the direction of the induced current.

Please Note:

1. Fleming’s left-hand rule is used for electric motors, while Fleming’s right-hand rule is used for electric generators.
2. In other words, Fleming’s left hand rule should be used if one were to create motion, while Fleming’s right hand rule should be used if one were to create electricity.

Alternating Current (AC) And Direct Current (DC)

Electric current flows in two ways – Alternating Current (AC) and Direct Current (DC). These are shown graphically in figure below:

Difference Between Alternating Current (AC) And Direct Current (DC)

Advantages Of Alternating Current (AC) Over Direct Current (DC)

1. DC current is normally available from a source like a battery. We cannot have large enough batteries to supply all our needs.
2. Electricity needs to be generated continuously to fulfil our needs. In AC, electricity is generated by the rotation of a coil in a magnetic field, whereas a DC generator requires brushes to convert the AC to DC within the machine. Thus, DC requires additional effort and energy.
3. Once electricity is generated, it needs to be transmitted over long distances. The transmission is more economical in AC
4. Coming to the last stage i.e. usage, though most of the consumers use electricity for lighting in which case AC or DC does not make a difference (that also depends based on the lighting device) the major demand of electricity is for mechanical power. That conversion (electrical to mechanical) is more easily and economically done by AC motor for similar reasons as an AC generator.

Due to the above reasons, use of AC is advantageous over DC.

Disadvantages of Alternating Current (AC) Over Direct Current (DC) – AC cannot be stored.

Domestic Electric Circuits) – Domestic electric circuits use three kinds of wires-

1. Live wire (positive) with red insulation cover.
2. Neutral wire (negative) with black insulation cover.
3. Earth wire with green insulation cover. Earth wire protects us from electric shock in case of leakage of current, especially in metallic appliances, by providing a low resistance path for flow of current in case of leakage.

The flow of current in the domestic circuit follows the following path (as shown in figure below):

PSEB Class 10 Physics Important Questions Chapter 4

Pole → Main Supply → Fuse → Electricity Meter → Distribution Box → To Separate Circuits

Note: The potential difference between Live wire and Neutral wire in India is 220V.

Short Circuit – Short circuit occurs when live wire accidentally comes in contact with neutral wire. Short circuit can occur due to following reasons:

1. Faulty Wire Insulation – If the insulation of wires is damaged, live wire may come in contact with a neutral wire, causing short circuit.
2. Damaged Or Loose Wire Connections – This may lead to overheating of the wires resulting in damage to the insulating coating of the wire, and hence short circuit.

Safety Devices To Prevent Short Circuit– Electric Fuse, Earth wire, MCB (Miniature Circuit Breaker).

Overloading– When current drawn is more than current carrying capacity of a conductor, it results in overloading.

Causes Of Overloading

1. Accidental hike in voltage supply.
2. Use of more than one device in a single socket.

Chapter 4 Magnetic Effects Of Current Reason- Assertion Questions And Answers

The following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below:

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Question 1. Assertion (A): On changing the direction of flow of current through a straight conductor, the direction of a magnetic field around the conductor is reversed.

Reason (R): The direction of magnetic field around a conductor can be given in accordance with left hand thumb rule.

Answer: 3. A is true but R is false.

Question 2. Assertion (A): The magnitude of the magnetic field at a point on the axis of a current carrying solenoid is inversely proportional to the current flowing through the solenoid.

Reason (R): The magnitude of the magnetic field at a point on the axis of a current carrying solenoid is directly proportional to the number of turns per unit length of a solenoid.

Answer: 4. A is false but R is true.

Question 3. Assertion (A): A compass needle is placed near a current-carrying wire. The deflection of the compass needle decreases when the magnitude of an electric current in the wire is increased.

Reason (R): Strength of a magnetic field at a point near the conductor increases on increasing the current.

Answer: 4. A is false but R is true.

Question 4. Assertion (A): The strength of the magnetic field produced at the centre of a current carrying circular coil increases on increasing the radius of the circular coil.

Reason (R): Magnetic field strength is inversely proportional to the radius of the circular coil.

Answer: 4. A is false but R is true.

Question 5. Assertion (A): Alternating Current is used in household supply.

Reason (R): AC electric power can be transmitted over long distances without much loss of energy.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Question 6. Assertion (A): A current carrying wire deflects a magnetic needle placed near it.

Reason (R): A magnetic field exists around a current carrying wire.

Answer: 1. Both A and R are true and R is the correct explanation of A.

PSEB Class 10 Science Chapter 4 Solutions

Chapter 4 Magnetic Effects Of Current Case Or Source-Based Questions And Answers

Question 1.

A solenoid is a long helical coil of wire through which a current is run in order to create a magnetic field. The magnetic field of the solenoid is the superposition of the fields due to the current through each coil. It is nearly uniform inside the solenoid and close to zero outside, and is similar to the field of a bar magnet having a north pole at one end and a south pole at the other, depending upon the direction of current flow. The magnetic field produced in the solenoid is dependent on a few factors such as the current in the coil, the number of turns per unit length, etc. The following graph is obtained by a researcher while doing an experiment to see the variation of the magnetic field with respect to the current in the solenoid. The unit of magnetic field as given in the graph attached is in milli-Tesla (mT) and the current is given in Ampere.

1) What type of energy conversion is observed in a linear solenoid?

1. Mechanical to Magnetic
2. Electrical to Magnetic
3. Electrical to Mechanical
4. Magnetic to Mechanical

Answer: 3. Electrical to Mechanical

2) What will happen if a soft iron bar is placed inside the solenoid?

1. The bar will be electrocuted, resulting in a short circuit.
2. The bar will be magnetised as long as there is current in the circuit.
3. The bar will be magnetised permanently.
4. The bar will not be affected by any means.

Answer: 2. The bar will be magnetised as long as there is current in the circuit.

3) The magnetic field lines produced inside the solenoid are similar to those of ______

1. A bar magnet
2. A straight current-carrying conductor
3. A circular current-carrying loop
4. Electromagnet of any shape

Answer: 1. A bar magnet

4) After analysing the graph, a student writes the following statements.

• The magnetic field produced by the solenoid is inversely proportional to the current.
• The magnetic field produced by the solenoid is directly proportional to the current.
• The magnetic field produced by the solenoid is directly proportional to the square of the current.
• The magnetic field produced by the solenoid is independent of the current.

Choose from the following which of the following would be the correct statement(s).

1. Only IV
2. I and III and IV
3. I and II
4. Only II

Answer: 4. Only II

5) From the graph, deduce which of the following statements is correct.

1. For a current of 0.8 A, the magnetic field is 13 mT
2. For larger currents, the magnetic field increases non-linearly.
3. For a current of 0.8 A, the magnetic field is 1.3 mT
4. There is not enough information to find the magnetic field corresponding to 0.8A current.

Answer: 1. For a current of 0.8 A, the magnetic field is 13 mT

Question 2. Ruchi fixes a sheet of white cardboard on a drawing board. She places a bar magnet in the centre of it. She sprinkles iron filings uniformly around the bar magnet. Then she taps the board gently and observes that the iron fillings arrange themselves in a particular pattern.

1) What does the pattern shape look like?

1. Straight lines
2. Squares
3. Closed curves
4. Parallel lines

Answer: 3. Closed curves

2) Why do iron filings arrange in a pattern?

1. Due to the poles of a magnet
2. Due to the force exerted by the magnet within its magnetic field
3. Due to repulsion between the poles and filings
4. None of the above

Answer: 2. Due to force exerted by the magnet within its magnetic field

3) What do the lines along which iron filings align represent?

1. Magnetic field lines
2. Magnetic force
3. Magnetic induction
4. Magnetic susceptibility

Answer: 1. Magnetic field lines

PSEB Class 10 Science Chapter 4 Solutions

4) What does the crowding of iron filings at the end of the magnet indicate?

1. The magnetic field is weak at the poles and stronger in the middle
2. The magnetic field is stronger at the poles and weaker at the middle
3. Magnetic field strength goes on decreasing from the north to the south pole
4. Magnetic field strength goes on decreasing from the south to the north pole

Answer: 2. The Magnetic field is stronger at the poles and weaker at the middle

5) How is the strength of the magnetic field is indicated?

1. Magnetic field strength cannot be indicated by magnetic field lines
2. Far the magnetic field lines, more is the magnetic strength
3. The closer the magnetic field lines are the magnetic field strength
4. The closer the magnetic field lines, more is the magnetic strength

Answer: 4. Closer the magnetic field lines, more is the magnetic strength

Question 3. The magnetic field at any point is the combined effect of the magnetic field due to the current in the wire and the magnetic field of the Earth. Iron filings, when placed near the wire carrying current, are arranged in circles due to the magnetic field produced by the current flowing through the wire. However, at a point far away from the wire, the magnetic field due to the Earth is predominant as compared to the magnetic field due to the current, due to which the iron filings are arranged in straight lines. The point where the two fields are equal and opposite is called the neutral point. At the neutral point, the net magnetic field is zero, and the compass needle at this point rests in any direction.

1) How are the magnetic field lines at the point near the straight current-carrying conductor?

1. A concentric circles pattern whose centre lies on a wire
2. Uniform and parallel line pattern
3. Spiral pattern
4. Zig-zag pattern

Answer: 1. Concentric circles pattern whose centre lies on the wire

2) To what parameter is the magnitude of the magnetic field produced by the straight conductor directly proportional?

1. Distance from the conductor
2. Strength of current in wire
3. External forces acting on the wire
4. Nature of material

Answer: 2. Strength of current in wire

3) Which rule is used to find the direction of the magnetic field produced by the straight current-carrying conductor?

1. Maxwell’s left-hand thumb rule
2. Maxwell’s right-hand thumb rule
3. Fleming’s left-hand rule
4. Fleming’s right-hand rule

Answer: 2. Maxwell’s right-hand thumb rule

4) What, according to the rule, will be the direction of the current when lines of the magnetic field are in the anti-clockwise direction?

1. Downward direction
2. Left direction
3. Upward direction
4. Right direction

Answer: 3. Upward direction

5) SI unit of magnetic field is

1. Gauss
2. Coulomb
3. Weber
4. Tesla

Answer: 4. Tesla

Question 4. The magnetic field at any point is the combined effect of the magnetic field due to the current in the wire and the magnetic field of the Earth. Iron filings, when placed near the wire carrying current, are arranged in circles due to the magnetic field produced by the current flowing through the wire. However, at a point far away from the wire, the magnetic field due to the Earth is predominant as compared to the magnetic field due to the current due to which the iron filings are arranged in straight lines. The point where the two fields are equal and opposite is called the neutral point. At the neutral point, the net magnetic field is zero and the compass needle at this point rests in any direction.

1. How are the magnetic field lines at the point near the straight current-carrying conductor?
2. To what parameter is the magnitude of the magnetic field produced by the straight conductor directly proportional?
3. Which rule is used to find the direction of the magnetic field produced by the straight current-carrying conductor?

Answer:

1. The magnetic field lines around the straight conductor carrying current are concentric circles whose centre lies on the wire.
2. The magnitude of the magnetic field is directly proportional to the current passing through the wire,
3. Maxwell’s right-hand thumb rule is used to find the direction of the magnetic field produced by a straight current-carrying conductor.

Question 5. Andre Marie Ampere suggested that a magnet must exert an equal and opposite force on a current-carrying conductor, which was experimentally found to be true. But we know that current is due to charges in motion. Thus, it is clear that a charge moving in a magnetic field experiences a force, except when it is moving in a direction parallel to it. If the direction of motion is perpendicular to the direction of magnetic field, the magnitude of force experienced depends on the charge, velocity (v), strength of the magnetic field (B), and sine of the angle between v and B. The Direction of magnetic force is given by Fleming’s left-hand rule.

1. If an electron is travelling horizontally towards east. A magnetic field in vertically downward direction exerts a force on the electron along which direction?

2. If a charged particle is moving along a magnetic field line, what would be the magnetic force on the particle?

3. A uniform magnetic field exists in the plane of paper pointing from left to right as shown in figure. In the field, an electron and a proton move as shown. Where do the electron and the proton experience the force?

Answer:

1. Fleming’s left hand rule is used to determine the direction of force on electron i.e., in south direction.
2. The angle between velocity and magnetic field is zero. Therefore, magnetic force on the particle is zero.
3. As the direction of current is taken opposite to the direction of motion of electrons, therefore, current from the motion of electron and proton is in the same direction, i.e., from bottom to top. Now, according to Fleming’s left hand rule, the electron and the proton experience forces both pointing into the plane of paper.

Question 6. A current-carrying wire produces a magnetic field around it. The phenomenon in which an electromotive force and current (if the conductor is in the form of a closed circuit) is induced by changing a magnetic field (or by passing magnetic field lines) through it is called electromagnetic induction. The emf so developed is called induced emf and the current made to flow is called induced current.

The cause of induced emf was discovered by Faraday and Flenry. It can be concluded that the induced current flows in a conductor as long as the magnetic lines of force change within the conductor. In case of relative motion i.e., motion of coil w.r.t to magnet or vice versa, the direction of the current flowing in the conductor is determined by the direction of the relative motion of the conductor with respect to the magnetic field. The induced emf or current is directly proportional to the rate of change in magnetic field.

1. A student connects a coil of wire with a sensitive galvanometer as shown in the figure. Where will he observe the deflection in the galvanometer of bar magnet?

2. A conducting rod AB moves across two magnets as shown in the figure and the needle in the galvanometer deflects momentarily. What is the name of this physical phenomenon?

3. A bar magnet is pushed steadily into a long solenoid connected to a sensitive meter.

Answer:

1. The deflection in the galvanometer can be seen if the bar magnet moves towards or away from the coil parallel to the axis of the coil.
2. If the needle of the galvanometer deflects, it means there is a change in a magnetic field and current is induced.
3. By Faraday’s law of electromagnetic induction, the e.m.f. induced in a conductor is proportional to the rate of change of magnetic lines of force linking the circuit. Hence, by pushing the magnet faster, the rate of change of magnetic lines will increase. This results in larger induced e.m.f.., and hence, larger deflection of the meter.

PSEB Class 10 Biology Solutions For Chapter 3 Electricity

Electric Current (I)

The amount of electric charge (electrons or ions) flowing through a particular area in a unit time is called electric current. Since in metals, electric charge flows through electrons, therefore, electric current can also be defined as the rate of flow of electrons in a metal (or conductor).

Points To Remember About Electric Current

1. In an electric circuit, the direction of flow of electric current is taken as opposite to the direction of flow of electrons. This is because electrons were not discovered when the phenomenon of electricity was first observed. The only sub-atomic particles known at that time were protons (Recall that protons are positively charged particles). So, electric current was considered to be the flow of positive charges, and the direction of flow of positive charges was taken to be the direction of electric current.
2. SI unit of electric current is ampere (A). One ampere is the amount of electric current flowing through an electric circuit when an electric charge (Q) of 1 coulomb flows through it in1 second.
3. Amount of electric current in an electric circuit is measured using Ammeter.
4. Ammeter is always connected in series in an electric circuit.

Electric Charge (Q) – It is the property of matter due to which matter experiences an attractive or a repulsive force when it is placed in an electromagnetic field. SI unit of electric charge is coulomb (C).

1. One coulomb is the charge contained in 1.6 x 10¹⁸ electrons (Note: Recall that charge on 1 electron = 1.6 x 10^-19C)

• Some examples of electric charge in daily life are as follows:
• Chattering sound produced by synthetic clothes – When the clothes made up of nylon are rubbed against some other fabric or against the wearer’s skin, static electricity is formed. This electrostatic force developed between the skin and the clothing particles is accountable for the chattering sound caused while removing such clothes.
• Development of electric charge on a rod – When a metal rod or glass rod is rubbed with a cloth, positive or negative charge develops on it. The type of charge developed depends on the material of the rod, For Example. If a glass rod is rubbed with a cloth, positive charge will develop, whereas if a metal rod is rubbed with a cloth, negative charge will develop.
• Feeling a short-term electric shock on touching some metal surface – When a person randomly touches a metallic surface (For Example, a doorknob), he or she is prone to feel a short-term electric shock. This is due to the existence of an electrostatic force between the doorknob and the person’s hand. Since the doorknob is made up of metal, it is capable of transferring the electrons to every object that comes in contact with it. This leads to the development of electrostatic interaction between the doorknob and the skin.
• Photocopy Machine – In a photocopy machine, the original paper is placed on a glass screen. The image of this original paper is transferred to a drum that is positively charged. The ink powder or the toner used is usually charged with a negative polarity. The drum rolls against the paper on which the impression is required to be created. The ink then gets transferred to the paper due to the electrostatic force of attraction, creating a photocopied image of the original document.

PSEB Class 10 Physics Solutions Chapter 3

Relation Between Electric Current (I) And Electric Charge (Q)

If a charge Q flows through a conductor of any cross-section in time (t), then the electric current (I) through the cross-section is given by the equation

I = Q/t

Potential Difference Or Voltage (V)

It is defined as the work involved or the energy released in the transfer of a unit quantity of electricity (.e, charge) from one point to the other, i.e.,

Potential difference = Work done/ Charge

Or, V = W/Q

• SI unit of potential difference is volt (V).
• One volt is the potential difference between two points in a current-carrying conductor when 1 joule of work is done to move a charge of1 coulomb from one point to another in an electric circuit, i.e.,
  • 1 volt = 1 joule/ lcoulomb
  • Or, 1V = 1JC^-1
• Potential difference in an electric circuit is measured using an instrument called Voltmeter. Voltmeter is always connected in parallel in the circuit.

Cause Of Potential Difference

The generation of potential difference across the terminals of the cell occurs due to the chemical action within a cell or battery.

Important Points About Electric Circuit

1. An electric circuit converts electrical energy into other forms of energy, For Example. in a bulb, electrical energy is converted into light energy and thermal energy.
2. It has at least two parts – a voltage source (e.g. a cell or a battery) and a conductor (i.e., wires).
3. Switches in the electrical circuits control the flow of current. When the switch is turned on, the circuit is closed and current can flow through it. When the switch is turned off, the circuit is open and current cannot flow through it.
4. An electric circuit can function only if it forms a closed loop from the battery and back again as shown:

Circuit Diagram

It is a graphical display of an electric circuit using either basic images of parts or industry-standard symbols. A simple circuit diagram consists of multiple parts such as cell or battery, switches, wires, electric components such as an ammeter or a voltmeter, a bulb, etc as shown in the figure below:

Important Points About Circuit Diagrams

1. In a circuit diagram, the direction of current is always from positive to negative terminal of the battery or cell (Recall that electrons will follow in opposite direction).

2. The longer end of the battery is the positive terminal and the shorter end of the battery is the negative terminal.

3. The positive end of the ammeter or voltmeter is connected to the positive end of the battery or cell and their negative end is connected to the negative end of the battery.

Circuit Diagram Symbols

Series And Parallel Electric Circuits

These are the two types of electric circuits. They differ in the number of loops through which current can flow.

Ohm’s Law

It gives the relationship between potential difference (V) and the current (I).

Ohm’s law states that the current (I) through a conductor between two points is directly proportional to the potential difference (V) across the two points, provided that the temperature remains the same, i.e,

V aI

or, V = IR (1)

where R is constant for the given metallic wire at a given temperature, and is called its resistance.

Resistance (R) – It is the property of a conductor to resist the flow of charge through it.

• SI unit of resistance is ohm (0).
• 1 Ohm is the resistance of a conductor when a potential difference of1 volt is applied across its ends, producing a current of 1 ampere.
• Resistance (R) of a conductor depends on the following factors:
  • Length (I) of the conductor, i.e., R oc I
  • Area of cross-section or thickness (A) of the conductor, i.e., R oc 1/A, and
  • Nature of the material of the conductor.

Combining factors (1) and (2), we get

∴ \(R \propto \frac{l}{A} \quad \text { or, } \quad R=\rho \frac{l}{A}\)

where p (rho) is a constant of proportionality and is called the ELECTRICAL RESISTIVITY of the material of the conductor. SI unit of resistivity is Q m. Resistivity is a characteristic property of the material.

• Metals and alloys have very low resistivity. They are good conductors of electricity.
• Insulators (For Example, rubber and glass) have intermediate resistivity.
• Resistivity of an alloy is generally higher than that of its constituent metals. Alloys do not oxidise (burn) readily at high temperatures. For this reason, they are commonly used in electrical heating devices, like electric iron, toasters etc.
• Both resistance and resistivity of a material vary with temperature.

Electricity PSEB Class 10 Notes

Difference Between Resistance And Resistivity

Effect Of Change In Resistance On Current

Resistance of a conductor is inversely proportional to the current (as can be deduced from equation i), i.e. R = V/I

Therefore, if the resistance is doubled, the current gets halved.

Resistor – It is a device having electrical resistance.

• Resistors are used in an electric circuit for protection, operation, or current control.
• Resistors can be connected in a series connection, in a parallel connection or in combinations of both series and parallel.
• Resistors always obey Ohm’s Law irrespective of the combination or complexity of resistor network.

Resistors In Series – Resistors are said to be connected in “Series”, when they are chained together in a single line as shown:

Resistors In Parallel – Resistors are said to be connected together in parallel when both of their terminals are respectively connected to each terminal of the other resistor or resistors, as shown:

Conductance (G) – The reciprocal of resistance is called conductance, i.e., G = 1/R

SI units of conductance are siemens (S).

Heating Effect Of Electric Current – When an electric current is passed through a conductor, the conductor becomes hot after some time due to the conversion of some electric energy into heat energy.

Cause Of Heating Effect Of Electric Current – Heating effect of electric current occurs due to collision of electrons in the conductor, as explained below:

• When a potential difference is applied across the ends of a conductor, its free electrons get accelerated in a direction opposite to the applied electric field.
• But the speed of the electrons does not increase beyond a certain speed because during the course of their motion they collide frequently with the positive metal ions.
• During these collisions between the free electrons and the metal ions, the kinetic energy of the moving electrons is transferred to the metal ions. As a result of this, the metal ions begin to vibrate about their mean position.
• Due to the vibrations of the metal ions about their mean positions, the kinetic energy of the metal ions increases. This in turn results in an increase in temperature, i.e., heating of the conductor.

Factors Affecting Heating Effect Of Current – The Heating effect of electric current depends on three factors:

1. Resistance Of The Conductor– The Higher the resistance more the heating effect.
2. Amount Of Current Flowing Through The Conductor– Higher the amount of current, more will be the heat generated.
3. Time For Which The Current Flows Through The Conductor – Longer the time for which current flows through the conductor more will be the heat generated.

Derivation of formula for heat produced by electric current flowing through a conductor

Consider the following circuit diagram:

Let I = current flowing through the circuit

R = Resistance of the resistor

V = Potential difference across the two terminals of the resistor

t = Time during which a charge Q flows across the circuit.

We know that

PSEB Class 10 Physics Important Questions Chapter 3

Potential difference (V) between two points = Work done (W)/Charge (Q)

Or, V = W/Q ….(1)

But Q = I x t, and V = I x R …..(2)

Substituting the values of Q and V from equation (2) in equation (1), we get

I x R = W/ I x t

Or, I x R x I x t = W

Or, W = I²Rt

Assuming that all the work done is converted into heat energy we can replace “W” with “H” in the above equation, to get

H = I²Rt

Uses Of the Heating Effect Of Electric Current

1. In Heating Devices such as electric iron, electric toaster, electric oven, electric kettle, electric heater, etc.
2. Electric heating is used to produce light in an electric bulb. Here, the filament must retain as much of the heat generated as is possible, so that it gets very hot and emits light. It must not melt at such high temperature. A strong metal with high melting point such as tungsten (melting point 3380°C) is used for making bulb filaments.
3. Electric fuse used in electric circuits – It protects circuits and appliances by stopping the flow of any unduly high electric current. FUSE IS ALWAYS PLACED IN SERIES WITH THE DEVICE. A fuse consists of a piece of wire made of a metal or an alloy of appropriate melting point, For Example., aluminium, copper, iron, or lead. If a current larger than the specified value flows through the circuit, the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit. The fuse wire is usually encased in a cartridge of porcelain or similar material with metal ends.

Disadvantages Of Heating Effect Of Electric Current

1. Undesirable as it converts useful electrical energy into heat. Thus, some energy gets wasted.
2. In electric circuits, the unavoidable heating can increase the temperature of the components and alter their properties.

Electric Power (P) – The rate at which electric energy is dissipated or consumed in an electric circuit is called electric power (P).

The formula for calculating electric power is:

P = V x I …..(1)

But according to Ohm’s law, V = I x R…..(2)

Substituting value of “V” from equation (2) in equation (1), we get

P = I x R x I

Or, P = I²R

But, I = V/R (from Ohm’s law), therefore

P = V²/R

SI unit of electric power is watt (W).

One watt is the power consumed by a device that carries 1 A of current when operated at a potential difference of 1 V.

Thus, 1 W = 1 volt x l ampere = 1 V A

Since, unit ‘watt’ is very small, we use a much larger unit called ‘kilowatt’ (1 kW = 1000 W).

Further, since electrical energy is the product of power and time, the unit of electric energy is, therefore, watt hour (W h).

One watt hour is the energy consumed when 1 watt of power is used for 1 hour.

Commercial Unit Of Electric Energy is Kilowatt hour (kWh), commonly known as ‘unit’.

1 kW h = 1000 watt x 3600 second = 3.6 x 106 watt second = 3.6 x 106 joule (J).

PSEB Class 10 Science Chapter 3 Solutions

Chapter 3 Electricity Reason- Assertion Questions And Answers

The following questions consist of two statements -Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below:

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Question 1. Assertion (A): Tungsten metal is used for making filaments of incandescent lamps.

Reason (R): The melting point of tungsten is very low.

Answer: 3. A is true but R is false.

Question 2. Assertion (A): When the resistances are connected end-to-end consecutively, they are said to be in series.

Reason (R): In case the total resistance is to be increased, then the individual resistances are connected in series.

Answer: 2. Both A and R are true but R is not the correct explanation of A.

Question 3. Assertion (A): When the resistances are connected between the same two points, they are said to be connected in parallel.

Reason (R): In case the total resistance is to be decreased, then the individual resistances are connected in parallel.

Answer: 2. Both A and R are true but R is not the correct explanation of A.

Question 4. Assertion (A): The fuse is placed in series with the device.

Reason (R): Fuse consists of a piece of wire made of a metal or an alloy of appropriate melting point.

Answer: 2. Both A and R are true but R is not the correct explanation of A.

Question 5. Assertion (A): The coil of a heater is cut into two equal halves and only one of them is used into heater. The heater will now require half the time to produce the same amount of heat.

Reason (R): The heat produced is directly proportional to square of current.

PSEB Class 10 Science Chapter 3 Solutions

Answer: 2. Both A and R are true but R is not the correct explanation of A.

Question 6. Assertion (A): A current carrying wire should be charged.

Reason (R): The current in a wire is due to flow of free electrons in a definite direction.

Answer: 4. A is false but R is true.

Question 7. Assertion (A): An Electron has a negative charge.

Reason (R): Electrons move always from a region of higher potential to a region of lower potential.

Answer: 3. A is true but R is false.

Question 8. Assertion (A): Heater wire must have high resistance and high melting point.

Reason (R): If resistance is high, the electric conductivity will be less.

Answer: 2. Both A and R are true but R is not the correct explanation of A.

Question 9. Assertion (A): In a chain of bulbs, 50 bulbs are joined in series. One bulb is removed now and circuit is completed again. If the remaining 49 bulbs are again connected in series across the same supply, then light gets decreased in the room.

Reason (R): Net resistance of 49 bulbs will be less than 50 bulbs.

Answer: 4. A is false but R is true.

Question 10. Assertion (A): The connecting wires are made of copper.

Reason (R): The electrical conductivity of copper is high.

Answer: 1. Both A and R are true and R is the correct explanation of A.

Chapter 3 Electricity Case Or Source-Based Questions And Answers

Question 1. The table shows the current in three electrical appliances when connected to a 240 V main supply.

1) Identify the electrical appliance having the highest electrical resistance

1. Electric lamp
2. Electric toaster
3. Electric kettle
4. Electric iron

Answer: 1. Electric lamp

2) Calculate the power rating of the kettle when connected to a 240 V main supply.

1. 2000 W
2. 2160 W
3. 3010 W
4. 200 W

Answer: 2. 2160 W

3) How much current would be drawn by an electric toaster when it is connected to a 120 V supply?

1. 4 A
2. 1 A
3. 10 A
4. 2A

Answer: 4. 2A

4) Calculate the power rating of the lamp when it is connected to a 240 V main supply.

1. 300 W
2. 120 W
3. 200 W
4. 240 W

Answer: 2. 120 W

5) 92 Watt = _____ J/S

1. 920
2. 9.2
3. 0.92
4. 92

Answer: 4. 92

PSEB Class 10 Science Chapter 3 Solutions

Question 2. In the below circuit, a nichrome wire of length ‘L’ is connected between points X and Y, and note the ammeter reading. The experiment is performed and repeated by inserting another nichrome wire of the same thickness but twice the length i.e., ‘2L’.

1) What are the changes observed in the ammeter readings?

1. Ammeter readings decreases, becomes half
2. Ammeter readings increases, becomes two times
3. Ammeter readings increases becomes quadrupled
4. Ammeter reading decreases becomes one- fourth

Answer: 1. Ammeter readings decreases, becomes half

2) What change is occurred in ammeter reading if instead of changing the length the area of cross- section is doubled?

1. Ammeter readings decreases, becomes half
2. Ammeter readings increases, becomes two times
3. Ammeter readings increases becomes quadrupled
4. Ammeter reading decreases becomes one -fourth

Answer: 2. Ammeter readings increases, becomes two times

3) If the resistors of 5 ohms and 10 ohms are connected in series in the above circuit. What is the ratio of the current passing through the two resistors?

1. 2:1
2. 3:1
3. 1:2
4. 1:1

Answer: 4. 1:1

4) If the resistors are connected in parallel

1. Current across each resistor is same and voltage changes
2. Current and voltage across each resistor is same
3. Current across each resistor varies and voltage remains same
4. Current changes, voltage changes

Answer: 3. Current across each resistor varies and voltage remains same

5) SI unit of current is denoted as

1. A
2. C
3. I
4. J

Answer: 1. A

Question 3. Sahil has two wires. Both wires are of the same material but are of different lengths and cross-sections. Sahil has to find the difference in their resistivities for various changes.

1) What is the difference in their resistivity’s for the above-mentioned condition?

1. Data given is insufficient to identify the change
2. Change in resistivity depends on change in length
3. Change in resistivity depends on change in area
4. No difference in resistivity’s as both wires are of same material

Answer: 4. No difference in resistivity’s as both wires are of same material

Explanation:

Resistivity’s depends on material of the conductor and not on its dimensions. So, both the wires will have same resistivity’s.

2) If Sahil stretches one of the wires, it becomes double the original length then is there any change in its resistances? If yes, what is the change?

1. Area reduces to half and resistance becomes four times the original value
2. Area becomes twice and resistance becomes four times the original value
3. Area becomes twice and resistance becomes 2 times the original value
4. Area decreased by half and resistance becomes 2 times the original value

Answer: 1. Area reduces to half and resistance becomes four times the original value.

3) If he stretches the other wire, it becomes triple its original length then how much is the change?

1. Area reduces to one- third and resistance becomes nine times the original value
2. Area becomes twice and resistance becomes four times the original value
3. Area becomes thrice and resistance becomes 3 times the original value
4. Area decreased by one- third and resistance becomes 9 times the original value

Answer: 4. Area decreased by one- third and resistance becomes 9 times the original value.

4) Sahil connect the two wires in series and observe change. What is the change? Why?

1. No change
2. Area increases
3. Area decreased by one- third and resistance becomes 9 times the original value
4. Resistance increases as area increases

Answer: 3. Area decreased by one- third and resistance becomes 9 times the original value.

Explanation: When wires are connected in series, there is increase in length. As resistance is directly proportional to length, resistance increases on increasing the length.

PSEB Class 10 Science Chapter 3 Solutions

5) Sahil connected the two wires in parallel and observe the change. What is the change? Give reason.

1. Resistance increases as length decreases
2. Resistance increases as length increases
3. Resistance decreases as area increases
4. Resistance increases as area increases

Answer: 3. Resistance decreases as area increases

Explanation: When wires are connected in parallel, the area increases and as we know that resistance is inversely proportional to cross-sectional area, resistance decreases.

Question 4. Sonia has a set of five substances. She has a chart stating resistivities of all the substances.

She has to choose an appropriate substance for performing electrical tasks. Which of the above substance according to you

1) Can be used as an insulator

1. A
2. B
3. B as well as C
4. E

Answer: 4. E

2) Can be used for domestic wiring

1. A
2. B
3. A as well as C
4. D

Answer: 3. A as well as C

3) Can be utilised in making solar cells and transistors

1. A
2. B
3. C
4. D

Answer: 4. D

4) Is an alloy

1. A
2. B
3. C
4. E

Answer: 2. B

5) Behaves as a semiconductor

1. A
2. D
3. C
4. E

Answer: 2. D

PSEB Class 10 Physics Solutions For Chapter 2 The Human Eye And The Colourful World

The Human Eye

Points To Remember About the Human Eye

1. The human eyeball is approximately spherical in shape. Its diameter is about 2.3 cm.
2. Eyes are located in eye sockets in the skull.
3. The human eye consists of the following parts:

Functioning Of The Human Eye

1. Light reflected by an object enters the eye through the cornea, and then passes the pupil.
2. The convex lens in the eye contracts or relaxes to focus the light onto the retina. Light is refracted as it passes through the convex lens. This causes the image that hits the retina to be reduced in size and flipped upside down.
3. Light-sensitive cells (rod and cone cells) present in the retina gather information and send electrical signals to the brain via the optic nerve.
4. Cells in the visual cortex of the brain flip the image from the retina, turning it the right way round.

PSEB Class 10 Physics Solutions Chapter 2

Pupil Reflex

The change in size of the pupil to control the amount of light entering the eye is called the pupil reflex.

Pupil reflex is initiated with the detection of the brightness of light entering the eye by the retina. It then passes an impulse to the brain through sensory neurones, the brain interprets the impulse.

and send back a message to the muscles of the iris through motor neurones, triggering a response, the change in size of the pupil due to contraction of radial or circular muscles. This is done to protect the eyes from damage.

Thus, in bright light, pupil size is reduced as too much light falling on the retina could damage it.

In dim light, pupil size is increased to allow as much light as possible to enter the eye.

Important Note for Students – Do not confuse the function of circular muscles and ciliary muscles. Remember that:

1. Circular muscles affect the size of the iris
2. Ciliary muscles affect the shape of the lens.

Power Of Accomodation

The ability of the eye lens to adjust its focal length to some extent by changing its curvature with the help of ciliary muscles is called accommodation. The amount of focusing needed by the lens depends on the distance of the object being viewed. Light from near objects requires a more convex lens than light from distant objects.

• For seeing Close Objects, ciliary muscles contract (Remember this using mnemonic CCC, meaning Ciliary muscles Contract for Close Vision). Due to this, the curvature of the eye lens increases, and it becomes thicker. Consequently, the focal length of the eye lens decreases. This enables us to see nearby objects clearly.
• For seeing Distant Objects, the ciliary muscles relax. Due to this, the curvature of the eye lens decreases and it becomes thin. Consequently, the focal length of the eye lens increases. This enables us to see distant objects clearly.

Near And Far Point

Thus, a normal eye can see objects clearly that are between 25 cm and infinity.

Why Do We Have Two Eyes For Vision And Not Just One?

• It gives a wider field of view. A human being has a horizontal field of view of about 150° with one eye and of about 180° with two eyes.
• Two eyes also provide a better detection of objects.

Note:

• Our two eyes are positioned on the front of our heads. This reduces our field of view in comparison to animals having their two eyes positioned on opposite sides of their heads.
• Each of our eyes sees a slightly different image because our eyes are separated by a few centimetres. The two images are combined into one by our brain, using the extra information, to tell us how close or far away things are.

Refractive Defects Of Vision And Their Correction

Refractive defects of vision occur due to partial loss of the power of accommodation of the eye.

Three common refractive defects of vision are – Myopia (Near-Sightedness), Hypermetropia (Far Sightedness) and Presbyopia.

The Human Eye And The Colourful World PSEB Class 10 Notes

Alternative ways to correct refractive defects of vision are:

• Use of contact lenses
• Eye surgery.

Note:

A person suffering from both myopia and hypermetropia requires bifocal lenses for correction. A common type of bifocal lenses consists of both concave and convex lenses, the upper portion consists of a concave lens to facilitate distant vision, and the lower part is a convex lens to facilitate near vision.

Cataract – It is an eye defect that occurs due to ageing. In this defect, the eye lens becomes milky and cloudy due to ageing, resulting in partial or complete loss of vision. This defect can be corrected only through cataract surgery.

Visual Impairment – Visual impairment means damage or malfunction of any part of the eye. It may occur due to damage to the cornea, pupil, eye lens, aqueous humour, vitreous humour, retina or optic nerve.

Eye Donation

Corneal blindness can be cured through corneal transplantation of donated eyes. Important points about eye donation are:

1. Anyone can donate eyes, independent of age or sex.
2. People using spectacles, or those who have undergone cataract surgery, can also donate eyes.
3. People having diabetes, hypertension, asthma and those without communicable diseases can also donate eyes.
4. Eyes must be removed within 4-6 hours after death. This is done by trained persons from eye bank at the home of the deceased or at a hospital.
5. Eye removal takes only 10-15 minutes and does not lead to any disfigurement.
6. The identities of both the donor and the recipient remain confidential.
7. One pair of eyes gives vision to up to FOUR CORNEAL BLIND PEOPLE. This is because one pair of eyes has various components, such as retina, cornea, and muscles, that can be transplanted to the corneal blind people to help in retaining their vision.
8. Persons having AIDS, Hepatitis B or C, rabies, acute leukaemia, tetanus, cholera, meningitis or encephalitis cannot donate blood.

Refraction Of Light Through A Prism

1. When light passes from air to the glass of the prism, due to the differences in the refractive index between the air and the glass, light bends once entering the prism.
2. Since the sides of the prism are angled, the light bends again when it exits the prism.
3. Different wavelengths of light refract differently.
4. Longer wavelengths refract less while shorter wavelengths refract more. Therefore, when a beam of white light is passed through a prism, different wavelengths of light get refracted in different angularly in order, resulting in the splitting of white light into a spectrum of seven colours (VIBGYOR starting from bottom) as shown:

Spectrum – It is defined as an orderly continuum of colours (VIBGYOR) formed due to the dispersion of white light through a prism.

The phenomenon due to which this splitting of white light into a spectrum of seven colours (VIBGYOR) occurs on passing through a glass prism is called DISPERSION.

Rainbow is an example of dispersion of sunlight by tiny water droplets (which act as small prisms) present in the atmosphere.

More About Rainbow

Rainbow is always formed in a direction opposite to that of the Sun.

A rainbow is formed due to three phenomenon – Refraction, Dispersion and Total Internal Reflection of light as shown in figure:

Total Internal Reflection – It is the phenomenon which occurs when the light rays travel from an optically denser medium to an optically rarer medium.

Scattering Of Light – The phenomenon of the spreading of light in different directions by colloidal particles is called scattering of light.

∴ \(\text { Scattering } \propto \frac{1}{\text { wavelength }}\)

Some phenomena that occur due to scattering of light are – the blue colour of the sky, the colour of water in the deep sea, the reddening of the sun at sunrise and the sunset.

Atmospheric Refraction

It is defined as the refraction of light caused by the bending of light rays through different angles on passing through different layers of the Earth’s atmosphere. Some effects of atmospheric refraction are:

1. Apparent flickering of objects placed behind hot air or fire- Air above a hot surface becomes hot and rises up. Its space is occupied by cool air. Since the refractive index of hot and cool air is different, atmospheric refraction occurs, and the object appears to flicker.

2. Stars near the horizon appear slightly higher than their actual position. The density of air decreases with height, i.e., at higher altitudes air particles can spread more, so air is optically rarer at higher altitudes.

PSEB Class 10 Physics Important Questions Chapter 2

Since light from a star coming from the horizon has to travel from an optically rarer to an optically denser medium, it will bend towards normal. As a result, stars appear higher.

Note: Planets do not twinkle because they are much closer to the Earth. Therefore, they nullify the twinkling effect.

3. Apparent flattening of the Sun’s disc at sunrise and sunset.

4. Advanced Sunrise and Delayed Sunset

The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction.

During Sunrise, the sun is rising above the horizon. The rays from the sun get refracted as they travel from an optically denser medium to an optically rarer medium.

This results in the bending of rays of light towards the normal. Since the human eye sees the sun rays as a straight line, it appears as the sun has risen, though it has actually not yet risen.

Due to the same reason, the Sun is visible to us about 2 minutes after the actual sunset.

Difference Between Dispersion, Scattering And Refraction

Tyndall Effect

It is the phenomenon of scattering of a beam of light by colloidal particles suspended in Earth’s atmosphere (For Example., smoke, tiny water droplets, dust particles and molecules of air). When a beam of light strikes such fine particles, the path of the beam becomes visible.

Some examples or applications of Tyndall effect in daily life are:

• Scattering of sunlight by tiny water droplets in the mist on passing through a canopy of a dense forest.
• Path of light becomes visible when light enters a dark and dusty room through a slit or ventilator.

The colour of the scattered light depends on the size of the colloidal particles.

1. Very fine particles scatter mainly blue light, i.e., shorter wavelength. Since the upper layers of the atmosphere contain very fine particles of water vapours and gases, these particles are effective in scattering of light of shorter wavelengths, i.e, blue. Due to this reason, if we look at the sky from the Earth, it appears blue to us.

However, skv appears dark to people flying at high altitudes and astronauts due to the absence of particles at such high altitudes, due to which scattering of light does not occur.

2. Particles of medium size mainly scatter red light, i.e., longer wavelength. Therefore, red is the least scattered light.

Since it is not scattered by dust particles and fog, the same colour can be seen up to a long distance. For this reason, danger signs are made in red colour.

3. Very large particles scatter all the wavelengths of light, due to which the scattered light appears white in colour. Clouds appear white because clouds are made up of water vapours which condense to form large water droplets.

Due to the large size of the water droplets, all wavelengths of light are scattered, and the clouds appear white.

Chapter 2 The Human Eye And The Colourful World Reason- Assertion Questions And Answers

For questions given below, two statements are given—one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (1), (2), (3) and (4) as given below.

1. Both A and R are true, and R is the correct explanation of the assertion.
2. Both A and R are true, but R is not the correct explanation of the assertion.
3. A is true, but R is false.
4. A is false, but R is true

Question 1. Assertion (A): Sunlight reaches us without dispersion in the form of white light and not as its components.

Reason (R): Dispersion takes place due to variation of refractive index for different wavelengths but in vacuu,m the speed of light is independent of wavelength and hence vacuum is non-dispersive.

Answer: 1. Both A and R are true, and R is the correct explanation of the assertion.

Question 2. Assertion (A): Stars appear to be twinkling and planets do not twinkle.

Reason (R): The blue colour scatters much more than the red colour by air particles.

Answer: 2. Both A and R are true, but R is not the correct explanation of the assertion.

Question 3. Assertion (A): A stick partly immersed in water appears to be bent.

Reason (R): Refraction of light when it passes from water into air.

Answer: 1. Both A and R are true, and R is the correct explanation of the assertion.

Question 4. Assertion (A): In a rainbow, light at the inner surface of the water drop gets internally reflected.

Reason (R): The angle between the refracted ray and the normal to the drop surface is greater than the critical angle.

Answer: 2. Both A and R are true, but R is not the correct explanation of the assertion.

PSEB Class 10 Science Chapter 2 Solutions

Question 5. Assertion (A): The Refractive index of glass with respect to air is different for red light and violet light.

Reason: The Refractive index of a pair of media depends on the wavelength of light used.

Answer: 1. Both A and R are true, and R is the correct explanation of the assertion.

Question 6. Assertion (A): When objects are observed through hot air, they appear to be moving slightly.

Reason (R): The hotter air is optically denser and the colder air is optically rarer.

Answer: 3. A is true, but R is false.

Question 7. Assertion (A): When white light passes through a glass prism, red colour is deviated the least.

Reason (R): Red colour has the minimum speed in the glass prism.

Answer: 3. A is true, but R is false.

Question 8. Assertion (A): The Sun appears white when it is overhead in the sky.

Reason (R): Light coming from the Sun has to travel a relatively shorter distance through the atmosphere to reach us.

Answer: 1. Both A and R are true, and R is the correct explanation of the assertion.

Question 9. Assertion (A): The blue colour of the sky appears due to the scattering of blue colour.

Reason (R): Blue colour has the shortest wavelength in the visible spectrum.

Answer: 1. Both A and R are true, and R is the correct explanation of the assertion.

Chapter 2 The Human Eye And The Colourful World Case Or Source-Based Questions

Question 1. Hypermetropia is a common eye condition where nearby objects appear blurred, but your vision is clearer when looking at things further away. If you feel your eyes are often tired and you have problems focusing on objects close to your eyes, you may have hypermetropia. A person is suffering from hypermetropia (long-sightedness). The near point of the person is 1.5 m. Assume that the near point of the normal eye is 25 cm.

1) The type of lens to be used in his spectacles is

1. Concave
2. Convex
3. Plano concave
4. Cylindrical

Answer: 2. Convex

2) The focal length of the lens he should use is

1. 20 cm
2. 30 cm
3. 40 cm
4. 50 cm

Answer: 2. 30 cm

3) The power of the lens is

1. 2.2 D ;
2. 1.1 D ;
3. 4.4 D ;
4. 3.3 D

Answer: 4. 3.3 D

4) What is another name for Hypermetropia?

1. Short-sightedness
2. Long-sightedness
3. Night blindness
4. Presbyopia

Answer: 2. Long-sightedness

5) A The power of a lens is +2.5 D. What kind of lens is it, and what is its focal length?

1. Concave lens, 100 cm
2. Concave lens, 40 cm
3. Convex lens, 40 cm
4. Convex lens, 50 cm

Answer: 3. Convex lens, 40 cm

Question 2. The spreading of light by the air molecules is called scattering of light. The light with the shortest wavelength scatters more. The sun appears red at sunrise and sunset; the appearance of blue sky is due to the scattering of light. The colour of the scattered light depends on the size of the particles. The smaller the molecules in the atmosphere, scatter smaller the wavelengths of light. The amount of scattering of light depends on the wavelength of light. When light from the sun enters the Earth’s atmosphere, it gets scattered by the dust particles and air molecules present in the atmosphere. The path of sunlight entering the dark room through a fine hole is seen because of the scattering of the sunlight by the dust particles present in its path inside the room.

1) To an astronaut in a spaceship, the colour of Earth appears

1. Red
2. Blue
3. White
4. Black

Answer: 2. Blue

2) At the time of sunrise and sunset, the light from the sun has to travel.

1. Longest distance of the atmosphere.
2. Shortest distance to the atmosphere
3. Both (1) and (2);
4. Can’t say

Answer: 1. Longest distance of the atmosphere

3) The colour of the sky appears blue, which is due to the

1. Refraction of light through the atmosphere
2. Dispersion of light by air molecules
3. Scattering of light by air molecules
4. All of these.

Answer: 3. Scattering of light by air molecules

4) At the time of sunrise and sunset

1. Blue colour is scattered, and red colour reaches our eyes
2. Red colour is scattered, and blue colour reaches our eyes
3. Green and blue are scattered, and orange reaches our eyes
4. None of these

Answer: 1. Blue colour is scattered and red colour reaches our eye

5) The danger signs are made red in colour, because

1. The red light can be seen from the farthest distance
2. The scattering of red light is the least
3. Both (1) and (2)
4. None of these

Answer: 3. Both (1) and (2)

Question 3. Atmospheric refraction is the phenomenon of the bending of light as it passes through Earth’s atmosphere. As we move above the surface of Earth, the density of air goes on decreasing. Local conditions like temperature, etc., also affect the optical density of Earth’s atmosphere. On account of atmospheric refraction, stars appear higher than they actually are; advanced sunrise; delayed sunset, oval appearance of the sun at sunrise and sunset; stars twinkle, planets do not.

PSEB Class 10 Science Chapter 2 Solutions

1) Due to atmospheric refraction, the apparent length of the day

1. Increases
2. Decreases
3. Remains the same
4. All of these

Answer: 1. Increases

2) The apparent position of the star appears raised due to

1. Atmospheric refraction
2. Scattering of light
3. Both (1) and (2)
4. None of these

Answer: 1. Atmospheric refraction

3) The sun appears oval-shaped or flattened due to

1. Dispersion
2. Scattering
3. Atmospheric refraction
4. Cannot say

Answer: 3. Atmospheric refraction

4) The twinkling of stars and the non-twinkling of planets is accounted for by

1. Scattering of tight
2. Dispersion of light
3. Atmospheric refraction
4. None of these

Answer: 3. Atmospheric refraction

5) In the absence of an atmosphere, the colour of the sky appears

1. Blue
2. Black
3. Red
4. Yellow

Answer: 4. Yellow

Question 4. When white light is incident on one refracting surface of the prism, the light splits up into constituent colours violet, indigo, blue, green, yellow, orange and red. The process of splitting white light into its seven constituent colours is called dispersion. When the dispersed white light is made to fall on a screen, we get a band of seven colours is called the spectrum of white light. Red colour bends the least on passing through the prism, and violet colour bends through the maximum angle on passing through the prism.

image

1) The splitting of white light can be done by

1. Fens
2. Prism
3. Mirror
4. None of these

Answer: 2. Prism

2) Which property of light is used by a prism to form a spectrum?

1. Reflection
2. Refraction
3. Dispersion
4. Scattering

Answer: 2. Refraction

3) When a red light passes through a prism, it

1. Will not split
2. Will split into seven colours
3. Will split into white colour
4. Will split into many different colours

Answer: 1. Will not split

4) The spectrum produced by the white light by a prism is called

1. Pure spectrum
2. Impure spectrum
3. Monochromatic spectrum
4. None of these

Answer: 2. Impure spectrum

Question 5. Millions of people in the developing countries of the world are suffering from corneal blindness, These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society in your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission, how would you contribute to this noble cause?

1) State the objective of organising such campaigns.

Answer: The objective of organising such a campaign is to make people aware and realize their duties towards society.

2) List two arguments that you would give to motivate people to donate their eyes after death.

Answer:

1. By donating our eyes after we die, we can light the life of a blind person.
2. One pair of eyes gives vision to two corneal blind people.

3) List two values which are developed in the persons who actively participate and contribute in such programmes.

Answer:

1. It shows the concern for others,
2. It also shows responsible behaviour towards society.