10th - PHYSICS

9. LIGHT – REFLECTION AND REFRACTION

SECTION- A
Select and write the most appropriate option out of the four options given for each of the questions 1 -
20.
1. The speed of light in a transparent medium is 0.6 times that of its speed in vacuum. The refractive
index
of the medium is
(a) 1.66 (b) 1.96 (c) 1.26 (d) 1.29
2. A student wants to project the image of a candle flame on a screen 80 cm in front of a mirror by
keeping
the candle flame at a distance of 20 cm from its pole. The magnification of the image produced is
(a) -4 (b) -2 (c) -6 (d) -1
3. The laws of reflection hold good for
(a) plane mirror only (b) concave mirror only
(c) convex mirror only (d) All mirrors irrespective of their shape.
4. All of the following statements are correct except
(a) The magnification produced by a convex mirror is always less than one
(b) A virtual, erect, same-sized image can be obtained using a plane mirror
(c) A virtual, erect, magnified image can be formed using a concave mirror
(d) A real inverted, same-sized image can be formed using a convex mirror
5. When an object was kept at position X in front of a concave mirror, an enlarged and virtual image was
formed. Which among the following identifies 'X' correctly?
(a) anywhere between the centre of curvature and principal focus
(b) anywhere between the pole and principal focus
(c) exactly at the centre of curvature
(d) exactly at the principal focus
6. The focal length of a spherical mirror having radius of curvature 30 cm is
(a ) 10 cm (b) 15 cm (c ) 30 cm (d) 60 cm
7. The ratio of the refractive index of red light to blue light in air is
(a) Less than unity (b) Equal to unity (c) Greater than unity
(d) Less as well as greater than unity depending upon the experimental arrangement
8. Choose the correct relation between u, v and R for spherical mirrors

9. The inner shining surface of a steel spoon serves as a

(a) Plane mirror (b) Concave mirror (c) Convex mirror (d) Any one of the above
10. The focal length of a combination of convex lens of power 1 D and concave lens of power -1 5 D is
(a) - 2m (b) 2 m (c) 2.5 m (d) 0.5 m
11. Which of the following graphs shows correct variation between the power (P) of a converging lens and
its focal length (f)?
12. SI unit of power of a lens is
(a) joule (b) dioptre (c) candela (d) watt
13. An object is placed at a distance f in the front of a convex mirror. If focal length of the mirror is f , then
distance of image from pole of the mirror is
(a) f (b) 2f (c) f /2 (d) f /4
14. The projection lens of a projector has focal length 5 cm. It is desired to get an image with a
magnification 30. The distance of the screen from the lens must be
(a) 0.3 m (b) 0.8 m (c) 1.55 m (d) 2.55 m
15. A combination of a concave and convex lens has power 5 D. If the power of convex lens is 4 D, then
focal length of the concave lens is
(a) 10 cm (b) 20 cm (c) 100 cm (d) 200 cm
16. Light rays A and B fall on optical component X and come out as C and D. The optical component is a

(a) concave lens (b) convex lens (c) convex mirror (d) prism

Question No. 17 to 20 consist of two statements – Assertion (A) and Reason (R). Answer these
questions selecting the appropriate option given below:
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true
17. Assertion : When light travels from one medium to another. The direction of propagation of light in
second medium changes.
Reason : Light travels with different speeds in different mediums.
18. Assertion : Power of a convex lens is positive and that of a concave lens is negative.
Reason : Convex lens forms real image and concave lens forms virtual image.
19. Assertion : A ray incident along normal to the mirror retraces its path.
Reason : In reflection, angle of incidence is not equal to angle of reflection.
20. Assertion : The mirror used in search lights are concave spherical.
Reason : In concave spherical mirror the image formed is always virtual.

SECTION-B
Question No. 21 to 26 are very short answer questions
21. A ray of light is incident on a convex mirror as shown. Redraw the diagram and complete the path of
this ray after reflection from the mirror. Mark angle of incidence and angle of reflection on it.

(OR)
Draw a diagram for light enters from rarer (air) to denser (glass slab),then denser to rarer and labelled it
22. Write down four important characteristics of image formed by a plane mirror.
23. For the same angle of incidence 45°, the angle of refraction in two transparent media; I and II is 20°
and 30° respectively. Out of I and II, which medium is optically denser and why?
24. A student focused the image of a candle flame on a white screen by placing the flame at various
distances from a convex lens. He noted his observations:

a. From the above table, find the focal length of lens without using lens formula
25. Name the type of mirrors used in the design of solar furnaces. Explain how high temperature is
achieved by this device.
26. AB and CD, two spherical mirrors, from parts of a hollow spherical ball with its center at O as shown in
the diagram. If arc AB = 1/2 arc CD, what is the ratio of their focal lengths? State which of the two
mirrors will always form virtual image of an object placed in front of it and why?

SECTION-C
Question No. 27 to 33 are short answer questions

27.Water has refractive index 1.33 and alcohol has refractive index 1.36. Which of the two medium is
optically denser? Give reason for your answer. Draw a ray diagram to show the path of a ray of light
passing obliquely from water to alcohol.
28. Draw a ray diagram in each of the following cases to show the formation of image, when an object is
placed and write the characteristics of images formed in each case .
(a) Between optical centre and principal focus of a convex lens.
(b) Between F and 2F of a convex lens
29. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the
needle placed in front of the lens, if image size is equal to the object size? Also, find the power of lens.
30. Focal length of a mirror is given by Focal length = Radius of curvature/2 Since both the mirrors have
same radius of curvature, therefore focal length of the two mirrors will be same, i.e., f1/f2 = 1/1 Since
virtual image is always formed by convex mirror. The mirror AB will always form virtual image.
31. An object 4 cm in height, is placed at 15 cm in front of a concave mirror of focal length 10 cm. At what
distance from the mirror should a screen be placed to obtain a sharp image of the object. Calculate
the height of the image.
32. (a) A concave mirror of focal length 10 cm can produce a magnified real as well as virtual image of an
object placed in front of it. Draw ray diagrams to justify this statement.
(b) An object is placed perpendicular to the principal axis of a convex mirror of focal length 10 cm. The
distance of the object from the pole of the mirror is 10 cm. Find the position of the image formed.
( OR )
What is meant by power of a lens? An object is placed at a distance of 15 cm from a convex lens of
focal length 20 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.
33. A student wants to project the image of a candle flame on the walls of school laboratory by using a
mirror. (a) Which type of mirror should he use and why?
 (b) At what distance in terms of focal length ‘f’ of the mirror should he place the candle flame
so as to get the magnified image on the wall.
(c) Can he use this mirror to project a diminished image of the candle flame on the same wall?
State ‘how’ if your answer is ‘yes’ and ‘why not’ if your answer is ‘no’.

SECTION-D
Question No. 34 to 36 are long answer questions
34. An object 5 cm tall was placed in front of a spherical mirror at 20 cm distance from the mirror. If a
virtual image of 10 cm tall was formed behind the mirror.
(i) Find the focal length of the mirror
(ii) Find the position of the images
(iii) Name the type of mirror used.
( OR )
It is desired to obtain an erect image of an object, using concave mirror of focal length 12 cm.
(i) What should be the object distance in the above case?
(ii) Will the image be smaller or larger than the object? Draw the ray diagram to show the formation of
the image.
(iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror?

35. a) The refractive indices of glass and water with respect to air are 3/2 and 4/3 respectively. If speed of
light in glass is 2 × 108 m/s, find the speed of light in water. b) The absolute refractive indices of
glass and water are 1.5 and 1.33 respectively. In which medium does light travel faster? Calculate
the ratio of speeds of light in the two media
( OR )
A student has focused the image of a candle flame on a white screen using a concave mirror. the
situation is a given below: Length of the flame = 1.5 cm, Focal length of the mirror = 12 cm, Distance
of flame from the mirror = 18 cm. If the flame is perpendicular to the principal axis of the mirror,
then calculate the following: (a) Distance of the image from the mirror (b) Length of the image If the
distance between the mirror and the flame is reduced to 10 cm, then what would be observed on the
screen? Draw ray diagram to justify your answer from this situation.

36. State the laws of refraction of light. Explain the term absolute refractive index of a medium’ and write
an expression to relate it with the speed of light in vacuum.
( OR )
To construct a ray diagram we use two light rays which are so chosen that it is easy to know their
directions after refraction from the lens. List these two rays and state the path of these rays after
refraction. Use these two rays to locate the image of an object placed between ‘f’ and ‘2f’ of a convex
lens.
SECTION - E
Question No. 37 to 39 are case-based/data -based questions with 2 to 3 short sub-parts.
Internal choice is provided in one of these sub-parts.
37. A concave lens is thick at the edges and thin at the centre, while a convex lens is thick at the centre
and thin at the edges. We can distinguish between a concave lens and a convex lens without touching
them. For this keep a book close to a lens and observe the image of the text of the book through the
lens. If the letters appear enlarged, then it is a convex lens and if the letters appear diminished then it is
a concave lens. Convex lens converges light rays and hence known as converging lens. Similarly, concave
lens diverges light rays and is known as diverging lens. Linear magnification produced by a lens is equal
to the ratio of the image distance to the object distance. Power of a lens is defined as the reciprocal of
its focal length.
(i) What type of image is always made by a concave lens ?
(ii) If magnification produced by a spherical lens is +0.75, then what is the nature of the lens ?
(iii) What is the power of a convex lens with focal length 80 cm ?
 ( OR )
(iii) What kind of lens is present in human eye ?

38. When light ray goes from one transparent medium to another transparent medium, it suffers a
change in direction, into second medium. The extent of the change in direction suffered by the
phenomenon of change in the path of light rays when going from one medium to another medium is
known as refraction. Ray is a given pair of media can be expressed in terms of refractive index. The
refractive index is related to an important physical quantity in the relative speed of light in different
media.
(i) A ray of light enters into the glass from air. Does it bend towards normal ?
(ii) What is the unit of refractive index
(iii) Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass?
The speed of light in vacuum is 3×108 ms-1.
( OR )
(iii) When light goes from one medium to another, which of the three parameters, frequency,
wavelength,
velocity change ?

39. Hold a concave mirror in your hand and direct its reflecting surface towards the sun. Direct the light
reflected by the mirror on to a white card-board held close to the mirror. Move the card board back
and forth gradually until you find a bright, sharp spot of light on the board. This spot of the light is the
image of the sun on the sheet of the paper; which also termed as “Principal focus” of the concave
mirror.
a) List two applications of concave mirror.
b) If the distance between the mirror and the principal focus is 15 cm, find the radius of curvature of
the mirror.
c) Draw a ray diagram to show the type of image formed when an object is placed at Centre of
curvature of a concave mirror.
( OR )
c) Draw a ray diagram to show the type of image formed when an object is placed between infinite and
pole of a convex mirror.