# CBSE Class 10 Science Light Reflection and Refraction Assignment Set C

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## Assignment for Class 10 Physics Chapter 10 Light Reflection And Refraction

Class 10 Physics students should refer to the following printable assignment in Pdf for Chapter 10 Light Reflection And Refraction in Class 10. This test paper with questions and answers for Class 10 Physics will be very useful for exams and help you to score good marks

### Objective Questions

Question : Match the following with the correct response:

(1) Refraction                  (A) Bending of light
(2) Reflection                  (B) Velocity of light increases
(3) Rarer medium            (C) Bouncing back of light
(4) Denser medium         (D) Velocity of light decreases
a. 1-D, 2-A, 3-C, 4-B
b. 1-A, 2-C, 3-B, 4-D
c. 1-C, 2-B, 3-D, 4-A
d. 1-B, 2-D, 3-A, 4-C

Explanation: Refraction is the phenomenon of change in the direction of propagation of light when it passes from one transparent medium into another.
Reflection is the phenomenon of bouncing of light from the interface of an opaque medium. When a ray of light passes from a denser medium to a rarer medium, the velocity of light increases. When a ray of light passes from a rarer medium to a denser medium, the velocity of light decreases.

Question : Which of the following lens would you prefer to use while reading small letters found in a dictionary?
a. A convex lens of focal length 50 cm
b. A convex lens of focal length 5 cm
c. A concave lens of focal length 50 cm
d. A concave lens of focal length 5 cm

Explanation: A convex lens (converging lens) of focal length 5 cm should be used to read small letters in a dictionary. A convex lens of short focal length (5 cm) bends the light rays through large angles, by focussing them closer to the optical centre.

Question : An experiment to trace the path of a ray of light through a glass slab was performed by four students I, II, III and IV. They reported the following measurements of angle of incidence i, angle of refraction r and angle of emergence e. Which one of the students has performed the experiment correctly?

a. III
b. I
c. II
d. IV

Explanation: It is most accurate since ∠e is (nearly) equal to ∠i. The correct value of ∠e = 60o.

### Light Reflection And Refraction Assertion Reason Class 10 Science

A. Both assertion and reason are true, and reason is the correct explanation of assertion.
B. Both assertion and reason are true, but reason is not the correct explanation of assertion.
C. Assertion is true but reason is false.
D. Assertion is false and reason is true.

Question. Assertion (A): Mirror Formula cannot be used for Plane Mirrors
Reason (R): Plane Mirror is a Spherical Mirror of Infinite Focal Length.

Question. Assertion(A): Virtual images are always erect.
Reason (R) : Virtual images are formed by converging lenses only.

Question. Assertion (A): Convex mirror is preferred for rear view mirrors in vehicles.
Reason (R) :The field view of a convex mirror is lesser than that of concave mirror.

Question. Assertion(A) : Concave mirrors are used as make-up mirrors.
Reason (R) : When the face is held within the focus of a concave mirror, then a diminished image of the face is seen in the concave mirror.

Question. Assertion (A): Light changes its speed when it passes from one medium to another.
Reason (R): When a ray travels from vacuum to a medium, then refractive index is known as absolute refractive index.

Question. 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.

Question. Assertion (A): The angle of incidence for a ray of light having zero angle of reflection is two.
Reason (R): Refracting surfaces follow Snell’s Law.

Question. Assertion (A) : It is impossible to see virtual image with our naked Eye.
Reason (R) : The rays do not actually emanate from a virtual image.

Question. Assertion(A): Light travels faster in water than air
Reason (R): Water is denser than Air.

Question : Define one dioptre of power of a lens?
Answer : Power of a lens is one dioptre if focal length of a lens is 1m

Question : What is the name given to change of path of light with change of medium?
Answer : Refraction can change path of light with change of medium

Question : What is silvering of mirror?
Answer : Silvering of mirror means coating the surface of mirror with a thin layer of silver, aluminium or some other shiny, opaque material.

Question : Which lens bends a light ray more or less with a shorter or with longer focal length?
Answer : The lens with the shorter focal length bends the light more.

Question : Name some phenomenon associated with light during image formation by mirrors.

Question : Give the relation between focal length and radius of curvature.

Question : State lens formula and write it mathematically.
Answer : The relationship between object distance (u), image distance (v), and focal length of lens is known as lens formula. It is given by 1/v - 1/u = 1/f

Question : Define refraction of light.
Answer : The change in direction of light, when it travels from one medium to another medium is called refraction of light.

Question : Define lateral displacement.
Answer : Lateral displacement is the perpendicular distance between the incident ray and the emergent ray.

Question : Give uses of convex mirror.
Answer : (a) Used as rear view mirror in vehicles.
(b) Used to see full length image of a tall building.

Question : State laws of reflection.
Answer : Incident ray, reflected ray and normal at the point of incidence all lie in the same plane. The angle of incidence is equal to the angle of reflection.

Question : What are spherical mirrors?
Answer : Mirrors whose reflecting surface are part of a sphere are called spherical mirrors.

Question : What are the properties of image formed by a plane mirror?
Answer : Image is virtual and erect.
• Size of the image is equal to that of object
• Image is laterally inverted.
• The image formed by a plane mirror is always at the same distance as the object is in front of it.

Question : Define pole, centre of curvature, radius of curvature, principal axis, aperture, focus and focal length of a spherical mirror.
Answer : Pole: the centre of reflecting surface. It is represented by letter P. Centre of Curvature: The centre of the sphere of which the mirror forms the part.
Represented by “C”.
Radius of Curvature: The radius of the sphere of which the mirror forms the part.
Represented by “R”.
Principal axis: The straight line joining the pole (P) and the centre of curvature. It is normal to the mirror at its pole.
Aperture: The diameter of the spherical mirror is called its aperture. The reflecting surface of the mirror.
Focus: The point of the principal axis at which the rays parallel to principal axis meet (concave mirror) or appear to meet (convex mirror) after reflection. Represented by F.
Focal Length: The distance between the pole and the principal focus of a spherical mirror is called focal length. Represented by f.

Question : Define refractive index.
Answer : Refractive index is defined as the ratio of speed of light in medium 1 to the speed of light in medium 2 and is represented as n21 and is read as refractive index of medium 2 with respect to medium 1.
n21 = speed of light in medium 1/speed of light in medium 2.

Question : Define incident ray, reflected ray, normal ray, angle of incidence and reflection.
Answer : Incident ray – light which falls on the mirror/ polished surface is called incident ray.
Reflected ray – ray of light which goes back in the same medium after striking the surface is called reflected ray.
Normal – the perpendicular drawn to the reflecting surface is called normal at that point.
Angle of incidence – the angle between the incident ray and the normal is known angle of incidence.
Angle of reflection – the angle between reflected ray and the normal is known angle of reflection.

Question : State laws of refraction.
Answer : The ratio of sin of angle of incidence to the sin of angle of refraction for a light of given colour and for a given pair of media is constant. This is called Snell’s law.
i.e., sin i / sin r = Constant
The incident ray, refracted ray and the normal at the point of incidence lie on the same plane.

Question : State mirror formula and write it mathematically.
Answer : The relation between focal length of mirror, distance of the object and distance of the
image is known as mirror formula. It is given by
1/u + 1/v = 1/f
u = Image distance
ν = Object distance
f = Focal length

Question : Define magnification of mirror.
Answer : The ratio of height of the image to the height of the object is called magnification. It is represented by ‘m’.
m = Height of image (h′)/Height of object (h) = –v/u
Magnification of real image is negative and of virtual image is positive.

Question : What is the relation between optical density, refractive index and speed of light?
Answer : The medium with higher refractive index in which speed of light is less is known as optically denser medium and the medium with lower refractive index in which the speed of light is more is known as optically rarer medium.

Question : Define magnification of lens.
Answer : Magnification (m) = Height of image (h) / Height of object (h) = ν/u
For convex lens ‘m’ can be more than, less than or equal to one.
For concave lens ‘m’ is less than one.

Question : Define centre of curvature, principal axis, optical centre, aperture, focus and focal length for a lens.
Answer : (a) Centre of curvature: It is the centre of the spheres of which the each surface of the lens forms a part. Represented by C or 2f.
(b) Principal axis: An imaginary straight line passing through the two centres of curvatures.
(c) Optical centre: It is the central point of the lens. Represented by O.
(d) Aperture: It is the diameter of circular outline of a spherical lens.
(e) Focus: The point at which rays of light parallel to principal axis converges (convex lens) or appears to diverge (concave lens) after refraction. Represented by F.
(f) Focal length: The distance between focus and optical centre is called focal length. It is represented by f.

Question : With respect to air the refractive index of ice is 1.31 and that of rock salt is 1.54.
Calculate the refractive index of rock salt with respect to ice?

Question : When a plane mirror is placed horizontally on the levelled ground at a distance of 40 m from the foot of a tower, the top of the tower and its image in the mirror subtend an angle of 90° at the eye. What is the height of the tower?

From the picture, we see that the complementary angle of depression of the light ray is 45°.
So, if AB is the tower, and CB is the distance between the tower and the mirror, then, From the figure it is clear that tan 45o = h /40 (where h = AB is the height of tower)
1 = h/40
h = 40 cm

Question :  Form the image in case an object is moved from infinity to the concave mirror.
Answer :  Images formed by a concave mirror.
Object at Infinity. Two cases arise :
i. Object between F and P. A ray AD from A goes parallel to principal axis after reflection passes through F (rule 1). Another ray AE striking the mirror normally through C is reflected back (rule 3). They form virtual image of the object behind the mirror. The image is erect and enlarged.
Object between F and P. An erect, enlarged, virtual image is formed behind the mirror.
Images Formed by a Concave mirror
ii. Object at F. A ray AD parallel to principal axis passes through F. Another ray AE strikes the mirror normally at E is reflected back as it passes through C (Rule 3).
They form image of object AB at infinity. The image is very much enlarged and is real and inverted.

Object at E. Real, inverted, extremely enlarged image is formed at infinity.

iii. Object between F and C (f and 2f) A ray AD from object going parallel to principal axis is reflected towards F (Rule 1). Another ray AE through C is reflected back (Rule 3) forming image of A at A'. Similarly image of B is formed at B'. Image is real, inverted, enlarged and beyond C (2f) i.e. as shown in fig.

iv. Object at C i.e. at 2f. A ray AD from A parallel to principal axis after reflection from mirror passes through F (Rule 1). Another ray AD' from A through F, goes parallel to principal axis i.e. towards D'A' (rule 2) forming real, inverted image of AB at C i.e. at 2f. The image is of the same size as the object.
Object at C, Image is also at C. It is real.

v. Object beyond C. A ray AD from A parallel to principal axis after reflection passes through F (Rule 1), Another ray from A through C, ray AG is reflected back along the same path (Rule 3), forming real, diminished, inverted image of AB is formed at A'B', between F and C.
Object beyond C, a real, inverted diminished image between F and C, inverted at C and is of same size as that of object.

vi. When mirror is inclined so that the rays strike the mirror obliquely. The ray AB passing through F after reflection goes parallel to principal axis towards BA' (Rule 2). Another ray DE through C striking the mirror at E is reflected back. The two form an image at A' Image is real, inverted, extremely diminished and at F.
Object at infinity, image at F. It is real, inverted, very much diminished.

vii. When mirror is in parallel plane to the object. In such a case, rays from infinity come parallel to principal axis. After reflection they pass through principal focus F (Rule 1). Image is extremely small, it is real, inverted and at principal focus.

Question : Name the type of mirror used in the following situations:
(i) Rear view mirror in vehicles
(ii) Solar furnace
(iii) Torch
(iv) Solar cooker
(v) To get the full length image of tall building.
Answer : (i) Rear view mirror in vehicles – convex mirror as it gives virtual image, diminished and cover the wider view.
(ii) Solar furnace – concave mirror to concentrate all parallel beam of light.
(iii) Torch – concave mirror is used.
(iv) Solar cooker – concave mirror is used to concentrate the heat rays at a point.
(v) Convex mirror is used to view a full length tall building.

### HOTS Questions

Question. Nidhi wanted the image of her pencil to be double the size of its original size. Name the mirror used for getting such image.

Question. An incident ray makes an angle of 60° with the mirror. What is the angle of reflection?

Question. What are the two types of reflection?
Answer : (i) Regular (ii) Irregular

Question. Give characteristics of image formed by plane mirror
Answer : • Image is virtual and erect.
• Size is same as of the object.
• It is formed at same distance.

Question. Name two types of spherical mirror.
• Convex mirror

Question. Give uses of convex mirror.
Answer : • It is used as the rear view mirror in cars.
• It is used in street lights as it diverge the light over larger area.

Question. Why do we prefer a convex mirror as a rear view mirror in vehicles?
Answer : Convex mirrors are used as rear view mirror in cars because it produces erect and diminished image of the traffic behind the vehicle. It also gives a wider view.

Question. The magnification produced by a plane mirror is +1. What does this mean?
Answer : This means that the size of the image is equal to the size of the object.

VBQs

Question. In a small town fair Akshay took his friend and showed him a mirror in which his image showed upper half body very fat and lower body very thin. Akshay’s friend got upset but
Akshay explained him by showing his similar image in the mirror.

(a) Name two mirrors used in this fair shop.
(b) Name the mirror in which the size of image is small.
(c) What value of Akshay is reflected?

Answer : (a) Concave and convex mirror.
(b) Convex mirror gives small size image.
(c) Akshay showed compassion and empathy.

Question : In the set-up shown below, a clear image of a distant object is obtained on the screen. The focal length of the concave mirror is:

a. 9.4 cm
b. 9.9 cm
c. 9.8 cm
d. 11.4 cm
Explanation: f = 11.8 - 2 = 9.8 cm

Question :  How does the frequency of a beam of ultra-violet light change when it goes from air into glass?
a. None of these
b. Frequency decreases
c. Remains the same
d. Frequency increases
Explanation: The frequency of light depends on the source of light and remains the same during refraction. The speed of the light changes when a ray of light passes from one medium to another. The speed of light is higher in a rarer medium than a denser medium. A ray of light travelling from a rarer medium to a denser medium slows down, due to which there is a change in the wave-length.

Question. What is light?
Answer : Light is a form of electromagnetic radiation that causes the sensation of sight. It doesn’t require any material medium to travel.

Question. Define absolute refractive index.
Answer : When medium 1 is vacuum, then refractive index of medium 2 is considered with respect to vacuum. This is called absolute refractive index.

Question. Define reflection of light.
Answer : The phenomenon of coming back of light in the same medium after striking a plane and polished surface is called reflection of light.

Question. What is the magnification of a plane mirror?

Question. What is the radius of curvature of plane mirror?

40. Where should be an object placed in front of convex lens so as to use it as a magnifier?
Answer : Between the pole and the focal length.

Question. Define power of a lens.
Answer : The degree of convergence or divergence of light rays achieved by lens is expressed in terms of power. It is given by
P = 1/f f = focal length in metre

Question. Define optical density.
Answer : The ability of the medium to refract light is called optical density.

Question. What happens if a light falls on a glass slab making 90° at its surface?
Answer : It undergoes normal refraction that is there is no deviation in the light.

Question. Define a lens.
Answer : A transparent material bounded by two surfaces of which one or both surfaces are spherical forms a lens.

Question. What is the unit of refractive index?
Answer : It has no unit.

Question. If a convex lens is used to focus sunlight on a paper, where the paper should be placed so that it catches fire.
Answer : At the Principal focus.

Question. What do you observe when light ray passes through rectangular slab?
Answer : (a) Angle of incidence is equal to angle of emergence.
(b) Incident ray is parallel to the emergent ray.
(c) Lateral displacement is proportional to the thickness of glass slab.
(d) Lateral displacement is proportional to the angle of incidence.

Question. What is the S.I. unit of power? Define it.
Answer : The S.I. unit of power is dioptre denoted by “D” 1 dioptre is the power of a lens
whose focal length is 1 metre.
• Power of a convex lens is +ve
• Power of a concave lens –ve

Question. Give some uses of concave mirror.
(b) Used as shaving mirror.
(c) Used by dentist.
(d) Used in solar furnance.

Question. Three mirrors, one plane, one concave and one convex are lying on the table.
identify them without touching them or using any other apparatus or device?
Answer : Plane mirror produces the image of same size. Concave mirror produced the magnified image while the convex mirror will produce a diminished image

Question. The radius of curvature of a spherical mirror is 20 cm. what is its focal length?
Focal length (f)= R/2 = 20 cm/2 = 10 cm.

Question. A fish under water is viewing obliquely a fisherman standing on the bank of lake. Does the man look taller or shorter?
Answer : As light travels from rarer to denser medium, it bends towards normal and appears to come from greater height. Therefore, to fish under water man looks taller

Question. An object 1 cm high produces a real image 1.5 cm high, when placed at a distance of 15 cm from concave minor. Calculate the position of the image.
l.5 v = - 15x 1.5 = -22.5 cm

Question. A ray of light travelling in air enters obliquely into water. Does the light ray bend towards or away from the normal? Why?
Answer : The light bends towards the normal on entry into water. It is due to the fact that as compared to air, the water is optically denser medium.

Question. If the speed of light in vacuum is 3 × 108 ms-1, find the speed of light in a medium of absolute refractive index 1.5.
Answer : V1/V2 = n2/n1 0r V2/v1` = n1/n2
Here, v1 = 3 × 108 m/s, n1 = 1, n2 = 1.5
v2 = 2 × 108 m/s

Question. A concave mirror produces three times magnified real image of an object placed 10cm in front of it. Where is the image located?
Answer : Distance of object from concave mirror (u)= -10 cm.
Magnification (m) = -
3 m = -v/u
v = -mu = -(3) x (-10) = -30 cm

Question. Which phenomenon occurs when light falls on
(a) highly polished surface
(b) a transparent medium?
Answer : (a) Reflection of light.
(b) Refraction of light.

Question : What is the radius of curvature of the spherical mirror in the figure given, if PA = 10 cm?
Answer :  We know that radius of curvature is twice the focal length f, so
R = 2f = 2(PA) = 2(10) = 20 cm

Question : Can a plane mirror be called a spherical mirror?
Answer :  Yes, a plane mirror can be called a spherical mirror because it also obeys the laws of reflection just like the spherical mirror . The only difference is that the reflecting surface of spherical mirror is curved while that of plane mirror is straight having infinite focal length and infinite centre of curvature. It can be called a spherical mirror of radius of curvature equal to infinity.

Question : Distinguish between real and virtual image in a lens.

Question : If p, q and r denote the object distance, image distance and the radius of curvature respectively, of a spherical mirror, then find out the relation between them.
Answer :  From mirror formula, we have
1/f = 1/v + 1/u
Substitute the given values, we get

which is the required relation between the three variables.

Question : An object 2 cm high is placed at a distance of 16 cm from a concave mirror which produces a real image 3 cm high.
1. Find the position of the image.
2. What is the focal length of mirror?
Object height, h= +2 cm
Image height, h' = - 3 cm (real image hence inverted)
Object distance, u = -16 cm
Image distance, v -?
Focal length, f=?
(i) Position of image
From the expression for magnification
m = h'/h = v/u
We have, v = -u h'/h
Putting values, we get v = -(-16 ) X -3/2
v = -24 cm
The image is formed at distance of 24 cm in front of the mirror (negative sign means object and image are on the same side).
(ii) Focal length of mirror
Using mirror formula, Putting values, we get
Using mirror formula,

Question. With the help of a ray diagram show how a pencil appears when dipped in water.
A ray of light (as we see pencil in air passing into water) travels from rarer to denser medium i.e., from air to water, it bends towards the normal, hence the pencil appears to be bent in water as shown in the diagram.

Question. Write the position, nature and size of images formed by concave mirror.
Answer : Table: Image formation by a concave mirror for different positions of the object

Question. Give the sign conventions for spherical mirrors.

Question. What are the two types of lenses?
Answer : Spherical lens: combination of two spherical refracting surfaces.

Question. Write nature, position and relative size of image formed by convex lens.
Answer : Table: Nature, position and relative size of the image formed by a convex lens for various positions of the object

Question. Write nature, position and relative size of image formed by cancave lens.
Answer : Table: Nature, position and relative size of the image formed by a concave lens for various positions of the object

Question. Draw a ray diagram of image formed when an object is placed in front of convex lens
(i) beyond 2 f and (ii) between f and 2f.

Question. Give sign conventions for spherical lenses.

Question. Complete the following ray diagrams:

Question. 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
(a) away from the screen
(b) towards the screen
(c) to a position very far away from the screen.
(d) either towards or away from the screen depending upon the position of the object.

Question. 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 :
(a) ∠i > ∠r > ∠e
(b) ∠i = ∠e > ∠r
(c) ∠i < ∠r < ∠e
(d) ∠i = ∠e < ∠r

Question. 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 ?
(a) Only A
(b) Only B
(c) A and B
(d) B and C

Question. A student has focussed on the screen a 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.
(a) Virtual, erect, diminished and green shade
(b) Real, inverted, diminished and in violet shade
(c) Real, inverted, diminished and in blue shade
(d) Virtual, inverted, diminished and in blue shade

Question. 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.
(a) Convex mirror of focal length 12 cm
(b) Convex lens of focal length 24 cm
(c) Concave mirror of focal length 24 cm
(d) Convex lens of focal length 12 cm

Question. 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
(a) Concave lens of focal length 10 cm
(b) Convex lens of focal length 20 cm
(c) Concave mirror of focal length 10 cm
(d) Concave mirror of focal length 20 cm

Question. 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 almost 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) A
(b) B
(c) C
(d) D

Question. 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 :
(a) is parallel to the incident ray.
(b) is along the same direction of incident ray.
(c) gets deviated and bends towards the thinner part of the prism.
(d) gets deviated and bends towards the thicker part (base) of the prism.

Question. Match the following
Column I                           Column II
(a) Shaving mirror            (i) Convex mirror
(b) Diverging lens             (ii) Concave lens
(c) Converging lens          (iii) Concave mirror
(d) Shop security mirror   (iv) Convex lens
Answer : (a) (iii), (b) (ii), (c) (iv), (d) (i).

Question. Fill in the blanks
(a) The ratio of speed of light in vacuum to the speed of light in a medium is called ................... .
(b) When a ray of light travelling in glass enter into water. It is refracted .................. the normal.
(c) A .................. is used as a rear-view mirror.
(a) Refractive index, (b) away from, (c) diverging mirror.

Assertion and Reason Type MCQs :

Following questions consists of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
A. Both assertion and reason are true, and reason is the correct explanation of assertion.
B. Both assertion and reason are true, but reason is not the correct explanation of assertion.
C. Assertion is true but reason is false.
D. Assertion is false and reason is true.

Question. 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.

Question. Assertion (A): The angle of incidence for a ray of light having zero angle of reflection is two.
Reason (R): Refracting surfaces follow Snell’s Law.

Question. Assertion(A) : Concave mirrors are used as make-up mirrors.
Reason (R) : When the face is held within the focus of a concave mirror, then a diminished image of the face is seen in the concave mirror.

Question. Assertion(A): Light travels faster in water than air
Reason (R): Water is denser than Air.

Question. Assertion(A): The mirrors used in search lights are concave spherical.
Reason (R) : In concave spherical mirror the image formed is always virtual.

Question. Assertion (A): Light changes its speed when it passes from one medium to another.
Reason (R): When a ray travels from vacuum to a medium, then refractive index is known as absolute refractive index.

Question. Assertion(A): Virtual images are always erect.
Reason (R) : Virtual images are formed by converging lenses only.

Question. Assertion (A): The emergent ray is parallel to the direction of incident ray.
Reason (R): The extent of bending of the ray of light at the opposite parallel faces (air- glass interface and glass- air interface) of the rectangular glass slab is equal and opposite.

Question. Assertion(A) : The formula connecting u, v and f for a spherical mirror is valid in all situations for all spherical mirrors for all positions of the object.
Reason (R) : Laws of reflection are strictly valid for plane surfaces.

Question. An object is placed 75 cm from a converging lens of focal length 25 cm. What is the nature of the image ?
Answer : The image is real, inverted and diminished as the object is placed beyond 2f.

Question. Define the term angle of refraction.
Answer : The angle between the refracted ray and the normal at the point of incidence is called angle of refraction.

Question. Define the term angle of incidence.
Answer : The angle between an incident ray and the normal at the point of incidence is called angle of incidence.

Question. What is absolute refractive index ?
Answer : Refractive index of a medium with respect to vacuum is called absolute refractive index.

Question. What is relative refractive index ?
Answer : Refractive index of a medium with respect to another medium is called relative refractive index.

Question. Define power of a lens.
Answer : The power of a lens is a measure of the degree of convergence or divergence of light rays falling on it.It is also defined as the reciprocal of its focal length in metres.

Question. Write two different uses of concave mirrors.
Answer : The concave mirror is used as a shaving mirror and headlights of vehicles.

Question. Define the following terms related to spherical mirrors :
(a) Centre of curvature, (b) Pole and (c) Aperture.
Answer : (a) The centre of curvature of a spherical mirror is the centre of the sphere of which the mirror is a part.
(b) The pole of a spherical mirror is the geometric centre of the spherical surface of the mirror.
(c) The plane surface area of the mirror through which the light rays enter and fall on the mirror is called its aperture.

Question. (a) What is meant by magnification ? Write its expression.
(b) What is its sign for (i) real, (ii) virtual image ?
Answer : (a) The ratio of height of the image to the height of the object is called linear magnification.
If the height of the image is ‘I’ and that of the object is ‘O’, then the magnification ‘m’ is : ‘m‘ = I/O
(b) (i) For a real image, magnification is negative.
(ii) For a virtual image, magnification is positive.

Question. The absolute refractive indices of glass and water are 3/2 and 4/3 respectively. If the speed of light in glass is 2 × 108 ms-1, calculate the speed of light in (i) vacuum and (ii) water.
Answer : Given, ng= 4/3 and nw = 3/2
Speed of light in glass ( vg) = 2 × 108 ms-1
(i) Speed of light in vacuum, c = ng × vg =3/2 × 2 × 108 = 3 × 108 ms-1
(ii) Speed of light in water, vw = c/nw =3 × 108 / (4/3) = 2.25 × 108 ms-1

Question. “The magnification produced by a spherical mirror is -3”. List all information you obtain from this statement about the mirror/ image.
Negative sign of magnification indicates that the image is real and inverted. Since the image is real and inverted, the mirror is concave and magnification of -3 indicates that the image is magnified.

Q21. Draw ray diagrams to show the image formed by a concave lens for the object placed at
(i) infinity (ii) Between f and 2f of the lens.
Ans. (i) object at infinity (ii) object between f and 2f

Question. A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in closed contact with each other. Calculate the lens power of the combination.
Answer : f1=25cm=0.25 m f2= -10cm= - 0.1m
Power of convex lens, P1 = 1/f1=1/0.25=+4D
Power of concave lens, P2 = 1/f2=1/ -
0.1m=-10D
power of combination, P = P1 +P2 = 4D – 10D = -6D

Q22. Draw a ray diagram to show the path of light when it travels through glass slab.
Ans.

Incident ray I enters the glass slab forms an angle of incidence ‘i’. Its bends towards the normal and forms an angle of refraction ‘r’.
The emergent ray is parallel to the incident ray.

Question. An object is placed at a distance of 12 cm in front of a concave mirror of radius of curvature 30 cm. List four characteristics of the image formed by the mirror
Answer : Radius of curvature (R) = 30 cm, object distance is 12 cm in front of the mirror. Thus we can say that object is placed between focus and pole. Four characteristics of the image formed by die given concave mirror when object is placed between pole and focus are:
(i) Virtual (ii) Erect
(iii) Enlarged (iv) Image is formed behind the mirror

Question. Define power of a lens. What is its unit? One student uses a lens of focal length 25 cm and another of – 25 cm. What is the nature of the lens and its power used by each of them?
Answer : Power of a lens is its ability to converge or diverge the rays of light falling on it. P = 1/f where f is in metre. Its unit is Dioptre. ! Diopter is the
power of a lens whose focal length is 1meter Lens is convex in the first case as f is positive and concave in the second case as f is negative. P1=1/0.25= 4D
P2=1/-0.25=-4D

Q23. Draw the following diagram in your answer book and show the formation of image of the object AB with the help of suitable rays.

Ans.

Question. List two possible ways in which a concave mirror can produce a magnified image of an object placed in front of it. State the difference if any between these two images.
A concave mirror can produce a magnified image of an object when object is placed:
(1) In between its pole and its focus
(2) In between its focus and its centre of curvature.
Difference,between these two images:
The image produced in first case will be virtual and erect. The image produced in second case will be real and inverted

Q26. (a) It is desired to obtain an erect image of an object using a concave mirror of focal length 20 cm.
(i) What should be the range of distance of the object from the mirror?
(ii) Will the image be bigger or smaller than the object?
(iii) Draw a ray diagram to show the image formation in this case.
(b) One-half of a convex lens of focal length 20 cm is covered with a black paper.
(i) Will the lens produce a complete image of the object?
(ii) Show the formation of image of an object placed at 2F1 of such covered lens
with the help of a ray diagram.
(iii) How will the intensity of the image formed by half covered lens compare with
non-covered lens? (CBSE 2008)
Ans.
(a) (i) Range of the object distance is 0 to 20 cm from the pole.
(ii) Image will be bigger than the object.
(iii) Ray diagram:

Question. A convex lens of focal length 2.0 m can produce a magnified virtual as well as real image. Is this a correct statement? If yes, where shall the object be placed in each case for obtaining these images?
Answer : Yes, it is correct.
If the object is placed within 2.0 m from the lens in the it forms magnified virtual image Between 2 m and 4 m it will form a real inverted and magnified image.

Q24. Draw ray diagrams to represent the nature, position and relative size of the image formed by a convex lens for the object placed:
(a) At 2F
(b) Between F1 and the optical centre O of lens
Ans.

(iii) Intensity will be reduced as the light falling on the lower (covered) portion will not reach the position of image.

Creating Based Questions

Question. Using the following information form a pathway showing the reflection of a spherical mirror. And also include information that is not mentioned below to complete it. Reflecting surface, spherical mirror,curved inwards, curved outwards, pole, centre of curvature.
Answer : Spherical mirror reflections → curved inwards or outwards. The reflecting mirrors → are curved inwards → called concave mirror. The reflection surface → of convex mirror → is curved outwards. Pole is the centre of reflecting surface. The centre of spherical mirror → known as centre of curvature.

Question. Using the following information form a pathway showing the formation of image by a convex mirror. And also include information that is not mentioned below to complete it. Convex, Infinity, position of image, size of image, Nature of image, between infinity and pole.
Answer : Two positions of objects → considered in the formation of image → by a convex mirror.
Position 1 : The position of object → at infinity → position of image is at the focus of F behind the mirror, size of the image is → highly diminished and point sized. The nature of image is → virtual and erect.
Position 2 : The position of object → between infinity and pole P → displays the image position between → P and F behind the mirror. Size of the image → is diminished. Nature of the image is → virtual and erect.

Question. Using the following information form a pathway showing the process of magnification in spherical mirror. And also include information that is not mentioned below to complete it. Magnification, spherical mirror, object image, ratio, height of image, positive, negative.
Answer : The spherical mirror magnifies → objects image to a relative extent with respect to object size. It is the ratio of → height of image → to the height of object. The positive sign in magnification value → denotes the virtual image. The negative sign in magnification value denotes → real image.

Question. Using the following information form a pathway showing the representation of an image in a spherical mirror. And also include information that is not mentioned below to complete it. Ray, centre of spherical mirror, reflection, light rays, reflecting surface.
Answer : In both concave and convex mirror → for the ray passing through the centre of curvature → the reflection is along same path. The reflection of light rays → is along same path → since the rays incident on the mirror → is normal to the reflecting surface.

Question. Using the following information form a pathway defining refractive index. And also include information that is not mentioned below to complete it. Ray of light, second medium, refractive index,speed, media, air.
Answer : The refractive index → is the extent of change in direction → in second medium of given media pair.
The propagation of light travels → with different speed in different media. The speed of light in air is → comparatively less when compared to vacuum.

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### CBSE Class 10 Physics Chapter 10 Light Reflection And Refraction Assignment

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