#### 12th Standard Physics English Medium Ray Optics Reduced Syllabus Important Questions With Answer Key 2021

12th Standard

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Physics

Time : 01:00:00 Hrs
Total Marks : 105
Multiple Choice Questions
15 x 1 = 15
1. An object is placed in front of a convex mirror of focal length of f and the maximum and minimum distance of an object from the mirror such that the image formed is real and magnified.

(a)

2f and c

(b)

c and $\infty$

(c)

f and O

(d)

None of these

2. For light incident from air on a slab of refractive index 2, the maximum possible angle of refraction is,

(a)

30o

(b)

45o

(c)

60o

(d)

90o

3. A plane glass is placed over a various coloured letters (violet, green, yellow, red) The letter which appears to be raised more is,Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm approximately. The maximum distance at which these dots can be resolved by the eye is, [take wavelength of light, λ = 500 nm]

(a)

1 m

(b)

5 m

(c)

3 m

(d)

6 m

4. A light bulb is placed between two mirrors (plane) inclined at an angle of 60°. Number of images formed are

(a)

2

(b)

4

(c)

5

(d)

6

5. A man of length h requires a mirror of length at least equal to, to see his own complete image

(a)

$\cfrac { h }{ 4 }$

(b)

$\cfrac { h }{ 2 }$

(c)

$\cfrac { h }{ 2 }$

(d)

h

6. Two plane mirror are at right angles to each other. A man stands between them and combs hair with his right hand. In how many of the images will he be seen using his right hand.

(a)

None

(b)

1

(c)

2

(d)

3

7. A ray of light is incidenting normally on a .plane mirror. The angle of reflection will be

(a)

(b)

90°

(c)

will not be reflected

(d)

None of these

8. What should be the angle between two plane mirror so that whatever be the angle of incidence, the incident ray and the reflected ray from the two mirrors be parallel to each other

(a)

60°

(b)

90°

(c)

120°

(d)

175°

9. Two plane mirrors A and Bare aligned parallel to each other, as shown in the figure. A light ray is incident at an angle of 30° at a point just inside one end of A. The plane of incidence coincides with the plane of the figure. The maximum number of times the ray undergoes reflections (including the first one) before it emerges out is)

(a)

28

(b)

30

(c)

32

(d)

34

10. One side of a glass slab is silvered as shown. A ray of light is incident one the other side at angle of incidence i = 45°. Refractive index of glass is given as 1.5. The deviation of the ray of light from its initial path when it comes out of slab is

(a)

90°

(b)

180°

(c)

120°

(d)

45°

11. A concave mirror of focal length 15 cm forms an image having twice linear dimensions of the object. The position of the object when the image is virtual will be

(a)

22.5 cm

(b)

7.5 cm

(c)

7.5 cm

(d)

45 cm

12. In a concave mirror experiment, an object is placed at a distance x, from, the focus and the image is formed at a distance x2 from the focus. The focal length of the mirror would be

(a)

xI x2

(b)

$\sqrt { { x }_{ 1 }{ x }_{ 2 } }$

(c)

$\cfrac { { x }_{ 1 }+{ x }_{ 2 } }{ 2 }$

(d)

$\sqrt { \cfrac { { x }_{ 1 } }{ { x }_{ 2 } } }$

13. Given a point source of light, which of the following can produce a parallel beam of light

(a)

Convex mirror

(b)

Concave mirror

(c)

Concave lens

(d)

Two plane mirrors inclined at an angle of 90°

14. A luminous object is placed 20 cm from surface of a convex mirror and a plane mirror is set so that virtual images formed in two mirrors coincide. If plane ~irror is at a distance of 12 cm from object. Then focal length of convex mirror, is

(a)

5 cm.

(b)

10 cm

(c)

20 cm

(d)

40 cm

15. A small piece of wire bent into an L shape with upright and horizontal portion of equal length, is placed with the horizontal portion along the axis of concave mirror whose radius of curvature is 10 cm. If the bend is 20 cm from the pole of mirror, then the ratio of lengths of the image of upright and horizontal position of the wire is

(a)

1: 2

(b)

3: 1

(c)

1: 3

(d)

2: 1

16. 2 Marks
10 x 2 = 20
17. What is angle of deviation due to refraction?

18. Why do stars twinkle?

19. What are mirage and looming?

20. What is Snell's window?

21. What is angle of deviation due to reflection?

22. It is possible for two lenses to produce zero power?

23. Is there any difference between coloured light obtained from prism and colours of soap bubble?

24. What is meant by angular dispersion?

25. A polaroid (I) is placed in front of a monochromatic source. Another polaroid (II) is placed in front of this polaroid (I) and rotated till no light passes. A third polaroid (III) is now placed in between (I) and (II). In this case, will light emerge from (II)? Explain

26. For the same angle of incidence, the angles of refraction in media P, Q and Rand 35°, 25°, 15° respectively. In which medium will the velocity of light be minimum?

27. 3 Marks
10 x 3 = 30
28. Describe the Fizeau's method to determine speed of light.

29. Obtain lens maker's formula and mention its significance.

30. Derive the equation for angle of deviation produced by a prism and thus obtain the equation for refractive-index of material of the prism.

31. What is dispersion? Obtain the equation for dispersive power of a medium.

32. Let us assume a person of height h is standing in front of a vertical plane mirror. The person could see his/her head when light from the head falls on the mirror and gets reflected to the eyes. Same way, light from the feet falls on the mirror and gets reflected to the eyes

33. What is the radius of the illumination when seen above from inside a swimming pool from a depth of 10 m on a sunny day? What is the total angle of view? [Given, refractive index of water is 4/3]

34. A biconvex lens has radii of curvature 20 cm and 15 cm each. The refractive index of the material of the lens is 1.5. What is its focal length? Will the focal length change if the lens is flipped by the side?

35. A monochromatic light is incident on an equilateral prism at an angle 30o and emerges at an angle of 75o. What is the angle of deviation produced by the prism?

36. Light ray falls at normal incidence on the first face of an equilateral prism and emerges gracing the second face. What is the angle of deviation? What is the refractive index of the material of the prism?

37. The wavelength of light from sodium source in vacuum is 5893Å.What are its (a) wavelength, (b) speed and (c) frequency when this light travels in water which has a refractive index of 1.33.

38. 5 Marks
8 x 5 = 40
39. Two light sources with amplitudes 5 units and 3 units respectively interfere with each other. Calculate the ratio of maximum and minimum intensities.

40. Find the minimum thickness of a film of refractive index 1.25, which will strongly reflect the light of wavelength 589 nm. Also find the minimum thickness of the film to be anti-reflecting.

41. What is the angle at which a glass plate of refractive index 1.65 is to be kept with respect to the horizontal surface so that an unpolarised light travelling horizontal after reflection from the glass plate is found to be plane polarised?

42. (I) For a glass ( $\mu =\sqrt { 5 }$) the angle of minimum deviation is equal to the angle of the prism. Find the angle ofthe prism.
(ii) Draw ray diagram when incident ray falls normally on one of the two equal sides of a right angled isosceles prism having refractive inded $\mu =\sqrt { 3 }$.

43. A ray PQ incident normally on the refracting face BA is refracted in the prism BAC made of material of refractive index 1.5.Complete the path of ray through the prism. From which face will the ray emerge? Justify your answer.

44. Two lenses of power +15 and - 5D are in contact with each otherforming a combination lens. (a) What is the focal length of this combination? (b) An object of size 3 cm is placed at 30 cm from this combination of lenses. Calculate the position and size of the image formed.zxc

45. Calculate the angle of dispersion between red and violet colours produced by a flint glass prism of refracting angle of 600• Given μ1=1.633 and = μr 1.622.

46. Light falls from glass (μ = 1.5) to air. Find the angle of incidence for which the angle of deviation is 900