Class 10 Science NCERT Light: Reflection and Refraction

Q 1 :

Study the given ray diagrams and select the correct statement from the following:

Device X is a concave mirror and device Y is a convex lens, whose focal lengths are 20 cm and 25 cm respectively.
Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 10 cm and 25 cm respectively.
Device X is a concave lens and device Y is a convex mirror, whose focal lengths are 20 cm and 25 cm respectively.
Device X is a convex lens and device Y is a concave mirror, whose focal lengths are 20 cm and 25 cm respectively.

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(4)

Since, for device X the light rays are coming from an object at infinity, passes through the device X and forms a real image on a screen on right side. Since, convex lens forms a real and inverted image at focus when object is at infinity. So, device X is converging lens or convex lens of focal length 20 cm.

For device Y, the beam of parallel rays from infinity is incident on the left side and after reflection a real image is formed on the screen. This device should be a mirror. Also, the light rays are getting converged, so mirror is converging in nature; it is a concave mirror of focal length 25 cm.

Q 2 :

A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens :

away from the screen
towards the screen
to a position very far away from the screen.
either towards or away from the screen depending upon the position of the object.

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(2)

As in order to get a sharp image the screen should be near to lens.

Q 3 :

Suppose you have focussed on a screen the image of candle flame placed at the farthest end of the laboratory table using a convex lens. If your teacher suggests you to focus the parallel rays of the Sun, reaching your laboratory table, on the same screen, what you are expected to do is to move the :

lens slightly towards the screen
lens slightly away from the screen
lens slightly towards the sun
lens and screen both towards the sun

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(1)

Since, candle is at the farthest end but not at the infinity. So, image will be formed between focus and centre of curvature of lens, but parallel rays from sun will converge at the focus. So, the distance between lens and screen should be reduced to get the image of the Sun.

Q 4 :

Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?

15 cm in front of the mirror
30 cm in front of the mirror
Between 15 cm and 30 cm in front of the mirror
More than 30 cm in front of the mirror

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(2)

In case of a concave mirror, image size becomes equal to the object size when the object distance equals to the radius of curvature i.e., twice the focal length.

So, the object has to be placed at a distance of (15 × 2) = 30 cm in front of a concave mirror.

Q 5 :

Which of the following statement is incorrect?

The bending of a ray of light on passing from different media to one is called reflection.
The phenomenon of splitting of white light into seven constituent colours is known as the dispersion of light.
Refractive index of medium depends upon its temperature.
Refractive index is directly proportional to the density of the medium.

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(1)

Bending of a ray of light on passing from one media to another is called refraction.

Q 6 :

A piece of red cloth when suitably illuminated may look black, but a piece of black cloth will never appear red. This phenomenon occurs because :

Black cloth reflects only black light
Black absorbs all the colours
Black cloth reflects all colours
Red cloth reflects all colours

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(2)

Black colour is a good absorber.

Q 7 :

Consider four mediums P, Q, R and S whose refractive indices are 2.14, 1.99, 2.98, and 2.16 respectively. Assume that if light travels from one medium to another. The rate of change will be utmost in which medium.

P to Q
Q to R
R to S
S to P

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(2)

As the difference in refractive indices is maximum.

Q 8 :

The refractive index $(η)$ of a colourless, volatile, non-polar solvent is 1.24 to the refractive index of a solid ice cube. The unmitigated refractive index of the ice cube is 1.31. Enumerate the unmitigated refractive index of the non-polar solvent.

1.6522
1.3241
1.6244
1.2401

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(3)

$μ_{p} = \frac{μ_{p}}{μ_{i}} 1.24 = \frac{μ_{p}}{1.31} μ_{p} = 13.1 \times 1.24 = 1.6244$

Q 9 :

Which of the following mirror is used by a dentist to examine a small cavity?

Convex mirror
Plane mirror
Concave mirror
Combination of convex and concave mirror

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(3)

As concave mirror gives the dentist a magnified reflection of the mouth while also refracting a bit of light. It forms an image in the mirror as larger, brightened and for the dentist easier to see.

Q 10 :

When light falls on a smooth polished surface, most of it

Is reflected in the same direction
Is reflected in different direction
Is scattered in all direction
Is refracted into the second medium

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(1)

This type of reflection is known as regular or specular reflection.

Q 11 :

A student very cautiously traces the path of a ray through a glass slab for different values of the angle of incidence $(∠ i) .$ He then measures the corresponding values of the angle of refraction $(∠ r)$ and the angle of emergence $(∠ e)$ for every value of the angle of incidence. On analysing these measurements of angles, his conclusion would be :

$∠ i > ∠ r > ∠ e$
$∠ i = ∠ e > ∠ r$
$∠ i < ∠ r < ∠ e$
$∠ i = ∠ e < ∠ r$

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(2)

As angle of incidence is equal to angle of emergence when light ray is passed through the prism, and angle of refraction is smaller than two.

Q 12 :

Three students A, B and C focussed a distant building on a screen with the help of a concave mirror. To determine focal length of the concave mirror they measured the distances as given below :
Student A : From mirror to the screen
Student B : From building to the screen
Student C : From building to the mirror

Who measured the focal length correctly ?

Only A
Only B
A and B
B and C

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(1)

A concave mirror always forms the image of a distant object at its focus.

Q 13 :

If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens.

The shape of the image of this object on the screen would be :

a
b
c
d

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4

(3)

Q 14 :

A student is performing the experiment of determining the focal length of a given concave mirror by focussing a distant tree on a screen. Which one of the following kinds of images he is likely to obtain on the screen?

A
B
C
D

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(2)

The image formed by concave mirror is real and inverted.

Q 15 :

A student has focussed on the screen of distant building using a convex lens. If he has selected a blue coloured building as object, select from the following options the one which gives the correct characteristics of the image formed on the screen.

Virtual, erect, diminished and green shade
Real, inverted, diminished and in violet shade
Real, inverted, diminished and in blue shade
Virtual, inverted, diminished and in blue shade

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(3)

As the image is focussed on screen, the image will be real, inverted and diminished but the colour of the image will remain same.

Q 16 :

A light ray enters from medium A to medium B as shown in figure. The refractive index of medium B relative to A will be:

greater than unity
less than unity
equal to unity
zero

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(1)

As the light ray when travelled from medium A to medium B, then they bend towards the normal which means that medium B has higher refractive index and less speed of light with respect to medium A. So, refractive index of medium B w.r.t. medium A will be greater than unity.

Q 17 :

An optical device has been given to a student and he determines its focal length by focusing the image of the sun on a screen placed 24 cm from the device on the same side as the sun. Select the correct statement about the device.

Convex mirror of focal length 12 cm
Convex lens of focal length 24 cm
Concave mirror of focal length 24 cm
Convex lens of focal length 12 cm

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(3)

The optical device is a concave mirror because when light rays from a distant object (like Sun) fall on this mirror, its image is formed at the focus of the mirror on same side as the object. Thus, the distance between the mirror and the screen is the focal length of the concave mirror. Hence, focal length of given device is 24 cm.

Q 18 :

Select from the following the best experimental set-up for tracing the path of a ray of light through a glass slab :

a
b
c
d

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(2)

To achieve best experimental set-up for tracing the path of a ray of light through a glass slab, the point of incidence should be in the middle of the glass slab and the incident angle should be close to 45°.

Q 19 :

When you focus the image of a distant flag, whose shape is given below, on a screen using a convex lens, the shape of the image as it appears on the screen is:

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(1)

As image is focused on the screen, then the image formed is real. And real images are inverted.

Q 20 :

A student determines the focal length of a device ‘X’ by focusing the image of a distant object on a screen placed 20 cm from the device on the same side as the object.
The device ‘X’ is:

Concave lens of focal length 10 cm
Convex lens of focal length 20 cm
Concave mirror of focal length 10 cm
Concave mirror of focal length 20 cm

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(4)

In case of the concave mirror, the image will be formed on the same side of the screen at its focus point when object is distant.

Q 21 :

A teacher sets up the stand carrying a convex lens of focal length 15 cm at 42.7 cm mark on the optical bench. He asks four students A, B, C and D to suggest the position of screen on the optical bench so that a distinct image of a distant tree is obtained immediately on it. The positions suggested by the students were as:

(A) 12.7 cm
(B) 29.7 cm
(C) 57.7 cm
(D) 72.7 cm

The correct position of the screen was suggested by:

A
B
C
D

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(3)

Focal length of convex lens

$f = 15 c m$

It is placed at 42.7 cm mark on optical bench.

When we want the distant objects to be focused, we get image at focus of convex lens.

Because rays from distant object are parallel rays and they get converged at focus.

$∴ P o s i t i o n o f s c r e e n = 42.7 + 15 = 57.7 c m 42.7 + 15 = 57.7 c m$

Q 22 :

A student has traced the path of a ray of light through a glass slab as follows. If you are asked to label 1, 2, 3 and 4, the correct sequencing of labeling ∠i, ∠e, ∠r and lateral displacement respectively is :

2, 1, 3, 4
1, 2, 3, 4
1, 3, 2, 4
1, 3, 4, 2

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4

(3)

Here 1 is angle of incidence, 3 is angle of emergence, 2 is the angle of refraction and 4 is the lateral displacement.

Q 23 :

In an experiment to trace the path of a ray of light through a triangular glass prism, a student would observe that the emergent ray :

is parallel to the incident ray.
is along the same direction of incident ray.
gets deviated and bends towards the thinner part of the prism.
gets deviated and bends towards the thicker part (base) of the prism.

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(4)

Student will observe that the emergent ray gets deviated and bends towards the thick parts (i.e., base) of the prism.

Q 24 :

Focal length of plane mirror is:

at infinity
zero
negative
None of these

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(1)

A plane mirror is a flat, reflecting surface. Thus, in case of plane mirror, when the parallel rays of light strike the mirror they get reflected back parallel to each other. So, they never meet, so we can say that they meet at infinity. So, the focal length of the plane mirror is infinity.

Topic Question Set

Q 1 :

Study the given ray diagrams and select the correct statement from the following:

Q 2 :

A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens :

Q 4 :

Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?

Q 5 :

Which of the following statement is incorrect?

Q 6 :

A piece of red cloth when suitably illuminated may look black, but a piece of black cloth will never appear red. This phenomenon occurs because :

Q 7 :

Consider four mediums P, Q, R and S whose refractive indices are 2.14, 1.99, 2.98, and 2.16 respectively. Assume that if light travels from one medium to another. The rate of change will be utmost in which medium.

Q 8 :

The refractive index $(η)$ of a colourless, volatile, non-polar solvent is 1.24 to the refractive index of a solid ice cube. The unmitigated refractive index of the ice cube is 1.31. Enumerate the unmitigated refractive index of the non-polar solvent.

Q 9 :

Which of the following mirror is used by a dentist to examine a small cavity?

Q 10 :

When light falls on a smooth polished surface, most of it

Q 13 :

If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens.

The shape of the image of this object on the screen would be :

Q 14 :

A student is performing the experiment of determining the focal length of a given concave mirror by focussing a distant tree on a screen. Which one of the following kinds of images he is likely to obtain on the screen?

Q 15 :

A student has focussed on the screen of distant building using a convex lens. If he has selected a blue coloured building as object, select from the following options the one which gives the correct characteristics of the image formed on the screen.

Q 16 :

A light ray enters from medium A to medium B as shown in figure. The refractive index of medium B relative to A will be:

Q 17 :

An optical device has been given to a student and he determines its focal length by focusing the image of the sun on a screen placed 24 cm from the device on the same side as the sun. Select the correct statement about the device.

Q 18 :

Select from the following the best experimental set-up for tracing the path of a ray of light through a glass slab :

Q 19 :

When you focus the image of a distant flag, whose shape is given below, on a screen using a convex lens, the shape of the image as it appears on the screen is:

Q 20 :

A student determines the focal length of a device ‘X’ by focusing the image of a distant object on a screen placed 20 cm from the device on the same side as the object.
The device ‘X’ is:

Q 22 :

A student has traced the path of a ray of light through a glass slab as follows. If you are asked to label 1, 2, 3 and 4, the correct sequencing of labeling ∠i, ∠e, ∠r and lateral displacement respectively is :

Q 23 :

In an experiment to trace the path of a ray of light through a triangular glass prism, a student would observe that the emergent ray :

Q 24 :

Focal length of plane mirror is:

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Topic Question Set

Q 1 : Study the given ray diagrams and select the correct statement from the following:

Q 2 : A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens :

Q 4 : Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?

Q 5 : Which of the following statement is incorrect?

Q 6 : A piece of red cloth when suitably illuminated may look black, but a piece of black cloth will never appear red. This phenomenon occurs because :

Q 7 : Consider four mediums P, Q, R and S whose refractive indices are 2.14, 1.99, 2.98, and 2.16 respectively. Assume that if light travels from one medium to another. The rate of change will be utmost in which medium.

Q 8 : The refractive index (η) of a colourless, volatile, non-polar solvent is 1.24 to the refractive index of a solid ice cube. The unmitigated refractive index of the ice cube is 1.31. Enumerate the unmitigated refractive index of the non-polar solvent.

Q 9 : Which of the following mirror is used by a dentist to examine a small cavity?

Q 10 : When light falls on a smooth polished surface, most of it

Q 13 : If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens. The shape of the image of this object on the screen would be :

Q 14 : A student is performing the experiment of determining the focal length of a given concave mirror by focussing a distant tree on a screen. Which one of the following kinds of images he is likely to obtain on the screen?

Q 15 : A student has focussed on the screen of distant building using a convex lens. If he has selected a blue coloured building as object, select from the following options the one which gives the correct characteristics of the image formed on the screen.

Q 16 : A light ray enters from medium A to medium B as shown in figure. The refractive index of medium B relative to A will be:

Q 17 : An optical device has been given to a student and he determines its focal length by focusing the image of the sun on a screen placed 24 cm from the device on the same side as the sun. Select the correct statement about the device.

Q 18 : Select from the following the best experimental set-up for tracing the path of a ray of light through a glass slab :

Q 19 : When you focus the image of a distant flag, whose shape is given below, on a screen using a convex lens, the shape of the image as it appears on the screen is:

Q 20 : A student determines the focal length of a device ‘X’ by focusing the image of a distant object on a screen placed 20 cm from the device on the same side as the object. The device ‘X’ is:

Q 22 : A student has traced the path of a ray of light through a glass slab as follows. If you are asked to label 1, 2, 3 and 4, the correct sequencing of labeling ∠i, ∠e, ∠r and lateral displacement respectively is :

Q 23 : In an experiment to trace the path of a ray of light through a triangular glass prism, a student would observe that the emergent ray :

Q 24 : Focal length of plane mirror is:

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Q 1 :

Study the given ray diagrams and select the correct statement from the following:

Q 2 :

A student obtains a blurred image of a distant object on a screen using a convex lens. To obtain a distinct image on the screen he should move the lens :

Q 4 :

Rays from sun converge at a point 15 cm in front of a concave mirror. Where should an object be placed so that size of its image is equal to the size of the object?

Q 5 :

Which of the following statement is incorrect?

Q 6 :

A piece of red cloth when suitably illuminated may look black, but a piece of black cloth will never appear red. This phenomenon occurs because :

Q 7 :

Consider four mediums P, Q, R and S whose refractive indices are 2.14, 1.99, 2.98, and 2.16 respectively. Assume that if light travels from one medium to another. The rate of change will be utmost in which medium.

Q 8 :

The refractive index $(η)$ of a colourless, volatile, non-polar solvent is 1.24 to the refractive index of a solid ice cube. The unmitigated refractive index of the ice cube is 1.31. Enumerate the unmitigated refractive index of the non-polar solvent.

Q 9 :

Which of the following mirror is used by a dentist to examine a small cavity?

Q 10 :

When light falls on a smooth polished surface, most of it

Q 13 :

If you focus the image of a distant object, whose shape is given below, on a screen using a convex lens.

The shape of the image of this object on the screen would be :

Q 14 :

A student is performing the experiment of determining the focal length of a given concave mirror by focussing a distant tree on a screen. Which one of the following kinds of images he is likely to obtain on the screen?

Q 15 :

A student has focussed on the screen of distant building using a convex lens. If he has selected a blue coloured building as object, select from the following options the one which gives the correct characteristics of the image formed on the screen.

Q 16 :

A light ray enters from medium A to medium B as shown in figure. The refractive index of medium B relative to A will be:

Q 17 :

An optical device has been given to a student and he determines its focal length by focusing the image of the sun on a screen placed 24 cm from the device on the same side as the sun. Select the correct statement about the device.

Q 18 :

Select from the following the best experimental set-up for tracing the path of a ray of light through a glass slab :

Q 19 :

When you focus the image of a distant flag, whose shape is given below, on a screen using a convex lens, the shape of the image as it appears on the screen is:

Q 20 :

A student determines the focal length of a device ‘X’ by focusing the image of a distant object on a screen placed 20 cm from the device on the same side as the object.
The device ‘X’ is:

Q 22 :

A student has traced the path of a ray of light through a glass slab as follows. If you are asked to label 1, 2, 3 and 4, the correct sequencing of labeling ∠i, ∠e, ∠r and lateral displacement respectively is :

Q 23 :

In an experiment to trace the path of a ray of light through a triangular glass prism, a student would observe that the emergent ray :

Q 24 :

Focal length of plane mirror is: