Question Set E

cbse 12th Standard Physics Ray Optics and Optical Instruments Important Questions And Answers Study Material - QB365

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Questions:

Multiple Choice Question

50 x 1 = 50

A man has height of 6 m. He observes image of 2 m height erect, then mirror used is

(a)

concave

(b)

convex

(c)

plane

(d)

None of these

The minimum magnifying power of telescope is M. If the focal length of its eye lens is halved, the magnifying power will become

(a)

m/2

(b)

(c)

(d)

A passenger in an aeroplane

(a)

should see a rainbow

(b)

may see a primary and a secondary rainbow as concentric circles

(c)

may see a primary and a secondary rainbow as concentric arcs

(d)

should never see a secondary rainbow

A thin prism P₁ with angle 6° and made from glass of refractive index 1.54 is combined with another thin prism P₂ of refractive index 1.72 to produce dispersion without deviation. The angle of prism P₂ will be

(a)

5°24'

(b)

4°30'

(c)

6°

(d)

8°

Dispersive power depends upon

(a)

the angle of prism

(b)

material of prism

(c)

deviation produced by prism

(d)

height of the prism

When light of wavelength \(\lambda\) is incident on an equilateral prism kept in, its minimum deviation position, it is found that the angle of deviation equals the angle of the prism itself The refractive index of the material of the prism for the wavelength \(\lambda\) is, then

(a)

\(\sqrt { 3 } \)

(b)

\(\frac { \sqrt { 3 } }{ 2 } \)

(c)

(d)

\(\sqrt { 2 } \)

A ray of light passes through an equilateral glass prism in such a manner that the angle of incidence is equal to the angle of emergence and each of these angles is equal to 3/4 of the angle of the prism. The angle of deviation is

(a)

45°

(b)

39°

(c)

20°

(d)

30°

A ray of light is incident at an angle of 60° on one face of a prism of angle 30°. The ray emerging out of the prism makes an angle of 30° with the incident ray. The emergent ray is

(a)

normal to the face through which it emerges

(b)

inclined at 30° to the face through which it emerges

(c)

inclined at 60° to the face through which it emerges

(d)

None of the above

A converging lens is used to form an image on a screen. When the upper half of the lens is-covered by an opaque screen, then

(a)

half the image will disappear

(b)

complete image will disappear

(c)

intensity of image will increase

(d)

intensity of image will decrease

10.

A biconvex lens has a focal length f. It is cut into two parts along a line perpendicular to principal axis. The focal length of each part will be

(a)

f/2

(b)

(c)

(3/2)f

(d)

11.

The minimum distance between an object and its real image formed by a convex lens is

(a)

1.5 f

(b)

2 f

(c)

2.5 f

(d)

4 f

12.

The real image which is exactly equal to the size of an object is to be obtained on a screen with the help of a convex lens of focal length 15 cm. For this, what must be in the distance between the object and screen?

(a)

15 cm

(b)

30 cm

(c)

45 cm

(d)

60 cm

13.

A plano-convex lens is made of glass of refractive index 1.5. The radius of curvature of its convex surface is R. Its focal length is

(a)

R/2

(b)

(c)

(d)

1.5R

14.

A glass slab has a critical angle of 30° when placed in air. What will be the critical angle when it is placed in liquid of refractive index 6/5?

(a)

45°

(b)

37°

(c)

53°

(d)

60°

15.

The critical angle of a prism is 30°. The velocity of light in the medium is

(a)

1.5 x 10⁸ m/s

(b)

3 x 10⁸ m/s

(c)

4.5 x 10⁸ m/s

(d)

None of these

16.

A vessel of depth 2 d cm is half filled with a liquid of refractive index \({ \mu }_{ 1 }\)and the upper half with a liquid of refractive index \({ \mu }_{ 2 }\)The apparent depth of the vessel seen perpendicu.

(a)

\(d\left[ \frac { { \mu }_{ 1 }{ \mu }_{ 2 } }{ { \mu }_{ 1 }+{ \mu }_{ 2 } } \right] \)

(b)

\(d\left[ \frac { 1 }{ { \mu }_{ 1 } } +\frac { 1 }{ { \mu }_{ 2 } } \right] \)

(c)

\(2d\left[ \frac { 1 }{ { \mu }_{ 1 } } +\frac { 1 }{ { \mu }_{ 2 } } \right] \)

(d)

\(2d\left[ \frac { 1 }{ { \mu }_{ 1 }{ \mu }_{ 2 } } \right] \)

17.

A spot is placed on the bottom of a slab made of a transparent material of refractive index 1.5. The spot is viewed vertically from the top when it seems to be raised by 2 cm. Then, the height of the slab is

(a)

10 cm

(b)

8 cm

(c)

6 cm

(d)

4 cm

18.

An object of size 7.5 cm is placed in front of a convex mirror of radius of curvature 25 cm at a distance of 40 cm. The size of the image should be

(a)

2.3 cm

(b)

1.78cm

(c)

1 cm

(d)

0.8 cm

19.

A convex mirror of focal length f forms an image which is 1/n times the object. The distance of the object from the mirror is

(a)

(n-1)f

(b)

\(\left[ \frac { n-1 }{ n } \right] f\)

(c)

\(\left[ \frac { n+1 }{ n } \right] f\)

(d)

(n+1)f

20.

An object is moving towards a stationary plane mirror with a speed of 2 m/s. Velocity of the image w.r.t. the object is

(a)

2 m/s towards right

(b)

4 rn/s towards right

(c)

2 rn/s towards left

(d)

4 rn/s towards left

21.

If the reflected ray is rotated by an angle of 4\(\theta\) in clockwise direction then the mirror was rotated by

(a)

2\(\theta\) in anti-clockwise direction

(b)

4\(\theta\) in anti-clockwise direction

(c)

2\(\theta\) in clockwise direction

(d)

4\(\theta\) in clockwise direction

22.

A ray of light travelling in a transparent medium of refractive index \(\mu\) on a surface separating the medium from air at an angle of incidence of 45⁰ For which of the following value of \(\mu\) the ray can undergo total internal reflection?

(a)

\(\mu\) = 1.33

(b)

\(\mu\) = 1.40

(c)

\(\mu\) = 1.50

(d)

\(\mu\) = 1.25

23.

Which of the following is not due to total internal reflection?

(a)

Difference between apparent and real depth of a pond

(b)

Mirage on hot summer days

(c)

Brilliance of diamond

(d)

Working of optical fibre

24.

A thin prism P₁ of angle 4^o and refractive index 1.54^o is combained with another thin prism P₂ of refractive index 1.72 to produce dispersion without deviation. The angle of P₂ is

(a)

4^o

(b)

5.33^o

(c)

2.6^o

(d)

3^o

25.

What is the refractive index of a prism whose angle A = 60⁰ and angle of minimum deviation d_m = 30⁰?

(a)

\(\sqrt{2}\)

(b)

\(\frac{1}{\sqrt{2}}\)

(c)

(d)

\(\frac{1}{\sqrt{3}}\)

26.

The focal length of objective lens is increased then magnifying power of

(a)

Microscope will increase but that of telescope decreases

(b)

Microscope and telescope both will increase

(c)

Microscope and telescope both will decrease

(d)

Microscope will decrease but that of telescope will increase

27.

The angle of a prism is A. One of its refracting

(a)

2 sin A

(b)

2 cos A

(c)

1/2 cos A

(d)

tan A

28.

Two identical thin plano-convex glass lenses each having radius of curvature of 20cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of refractive index 1.7. The intervening space is filled with oil refractive index 1.7. The focal length of the combination is

(a)

-20 cm

(b)

-25 cm

(c)

-50 cm

(d)

50 cm

29.

A convex lens has mean focal length 20 cm. The dispersive power of the material of the lens is 0.02. The longitudinal chromatic aberration for an object at infity, is

(a)

0.20

(b)

0.40

(c)

0.80

(d)

10³

30.

A hollow prism is filled with water and placed in air, It will deviate the incident rays

(a)

towards the base

(b)

away from base

(c)

parallel to base

(d)

towards or away from base depending on the location

31.

The r efracting angle of a prism is A and refractive index of the material of the prism is cot(A/2). The angle of minimum deviation is

(a)

180^o-3A

(b)

180-2A

(c)

90^o-A

(d)

180^o+2A

32.

The diameter of the moon is \(3.5\times10^3 km\) and its distance from the earth is \(3.8\times10^5 km\) seen by a telescope having focal lengths of the objective and the eye piece as 40mm and 1.0 cm respectively, the angular diameter of the image of the moon will be approximately.

(a)

2^o

(b)

10^o

(c)

20^o

(d)

None of these

33.

The refractive index of the material of a prism is \(\sqrt{2}\) and its refracting angle is 30⁰ . One of the refracting surfaces of the prism is made a mirror inwards. A beam of monochromatic light entering the prism from the other face will retrace its path after reflection from the mirrored surface,if its angle of incidence on the prism is

(a)

45⁰

(b)

60⁰

(c)

0⁰

(d)

30⁰

34.

A thin glass prism ( \(\mu \) = 1.5) is immersed in water ( \(\mu \) = 1.3). If the angle of deviation in air for a particular ray be D, then in water will be

(a)

0.2 D

(b)

0.3 D

(c)

0.5 D

(d)

0.6 D

35.

A thin prism of angle \({ 7 }^{ 0 }\) and refractive index 1.5 is combined with another prism of angle \(\theta \) and refractive index 1.7. The emergent ray goes undeviated. What is the value of \(\theta \) ?

(a)

\({ 3 }^{ 0 }\)

(b)

\({ 5 }^{ 0 }\)

(c)

\({ 9 }^{ 0 }\)

(d)

\({ 1 }^{ 0 }\)

36.

A glass prism ABC (refractive index 1.5), immersed in water (refractive index 4/3). A ray of light is incident normally on face AB. If it is totally reflected at face AC, then

(a)

\(sin\theta \ge \frac { 8 }{ 9 } \)

(b)

\(sin\theta \ge \frac { 2 }{ 3 } \)

(c)

\(sin\theta \ge \frac { \sqrt { 3 } }{ 2 } \)

(d)

\(\frac { 2 }{ 3 } \)

37.

If the critical angle for total internal reflection from a medium to vaccum is \({ 30 }^{ 0 }\), the velocity of light in the medium is

(a)

\(3\times { 10 }^{ 8 }m{ s }^{ -1 }\)

(b)

\(1.5\times { 10 }^{ 8 }m{ s }^{ -1 }\)

(c)

\(6\times { 10 }^{ 8 }m{ s }^{ -1 }\)

(d)

\(\sqrt { 3 } \times { 10 }^{ 8 }m{ s }^{ -1 }\)

38.

Two lamps of powers \({ P }_{ 1 }\)and \({ P }_{ 2 }\) are placed on either side of a paper having an oil spot. The lamps are at 1m and 2 m respectively, On either side of the paper and the oil spot is invisible. What is the value of \({ P }_{ 1 }/{ P }_{ 2 }\)?

(a)

0.25

(b)

0.40

(c)

0.50

(d)

0.60

39.

A thin convergent glass lens( \(\mu \) = 1.5) has a power of + 5.0 D. When this lens is immersed in aliquid of refractive index \(\mu \) it acts as a divergence lens of focal length 100 cm. the value of \(\mu \) should be

(a)

3/2

(b)

4/3

(c)

5/3

(d)

40.

If in a plano-convex lens, radius of curvature of convex surface is 10 cm and the focal length of the lens is 30 cm. The refractive index of the material of the lens will be

(a)

1.5

(b)

1.66

(c)

1.33

(d)

41.

A lens has focal length 10 cm. An object is placed 15 cm in front of it. Where should a convex mirror be placed, so that image is formed at the object itself, when focal length of convex mirror is 12 cm?

(a)

6 cm from lens

(b)

8 cm from lens

(c)

5 cm from lens

(d)

4 cm from lens

42.

The frequency of a light wave in a material and wavelength is 5000 A The refractive index of material will be

(a)

1.40

(b)

1.50

(c)

3.00

(d)

1.33

43.

A small coin is resting on the bottom of a beaker filled with a liquid. A ray of light from the coin travels up to the surface of the liquid and moves along its surface as shown in figure. How fast is the light travelling in the liquid?

(a)

\(1.8\times { 10 }^{ 8 }m{ s }^{ -1 }\)

(b)

\(2.4\times { 10 }^{ 8 }m{ s }^{ -1 }\)

(c)

\(3.0\times { 10 }^{ 8 }m{ s }^{ -1 }\)

(d)

\(1.2\times { 10 }^{ 4 }m{ s }^{ -1 }\)

44.

A 4 cm thick layer of water covers a 6 cm thick glass slab. Acoin placed at the bottom of the slab and is being observed from the air side along the normal to the surface. Find the apprent position of the coin from

(a)

7.0 cm

(b)

8.0 cm

(c)

10 cm

(d)

5 cm

45.

Aglass slab ( \(\mu \) = 1.5) of thickness 6 cm is placed over a paper. What is the shift in the letters?

(a)

4 cm

(b)

2 cm

(c)

1 cm

(d)

None of these

46.

In the given figure, the angle of reflection is

(a)

\({ 30 }^{ 0 }\)

(b)

\({ 60 }^{ 0 }\)

(c)

\({ 45 }^{ 0 }\)

(d)

None of these

47.

A Convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in dioptres of the combination is

(a)

(b)

(c)

infinite

(d)

zero

48.

The image formed by a convex mirror of focal length 30 cm is a quarter of the size of the object. The distance of the object from the mirror is

(a)

30 cm

(b)

90 cm

(c)

120 cm

(d)

60 cm

49.

A Concave mirror form the real image of an object which is magnified 4 times. The object is moved 3 cm away, the magnification of the image is 3 times. What is the focal length of the mirror?

(a)

3 cm

(b)

12 cm

(c)

36 cm

50.

A ray of light is successively deflected from two plane mirrors inclined to each other at a certain angle. If the total deviation in the path of the rays reflected from the two mirrors be \({ 300 }^{ 0 }\) , then what is the number of images formed ?

(a)

(b)

(c)

(d)

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Answers Key:

Multiple Choice Question

50 x 1 = 50

(b)
convex

(b)
2m

(b)
may see a primary and a secondary rainbow as concentric circles

(b)
4°30'

(b)
material of prism

(a)
\(\sqrt { 3 } \)

(d)
30°

(a)
normal to the face through which it emerges

(d)
intensity of image will decrease

10.

(d)
2f

11.

(d)
4 f

12.

(b)
30 cm

13.

14.

(b)
37°

15.

(a)
1.5 x 10⁸ m/s

16.

(b)
\(d\left[ \frac { 1 }{ { \mu }_{ 1 } } +\frac { 1 }{ { \mu }_{ 2 } } \right] \)

17.

18.

(b)
1.78cm

19.

(a)
(n-1)f

20.

(d)
4 rn/s towards left

21.

(a)
2\(\theta\) in anti-clockwise direction

22.

(a)
\(\mu\) = 1.33

23.

(a)
Difference between apparent and real depth of a pond

24.

(d)
3^o

25.

(a)
\(\sqrt{2}\)

26.

(d)
Microscope will decrease but that of telescope will increase

27.

(b)
2 cos A

28.

29.

(b)
0.40

30.

(a)
towards the base

31.

(b)
180-2A

32.

(a)
2^o

33.

(a)
45⁰

34.

(b)
0.3 D

35.

(b)
\({ 5 }^{ 0 }\)

36.

(a)
\(sin\theta \ge \frac { 8 }{ 9 } \)

37.

(b)
\(1.5\times { 10 }^{ 8 }m{ s }^{ -1 }\)

38.

(a)
0.25

39.

40.

41.

(a)
6 cm from lens

42.

43.

(a)
\(1.8\times { 10 }^{ 8 }m{ s }^{ -1 }\)

44.

(a)
7.0 cm

45.

(b)
2 cm

46.

47.

(d)
zero

48.

(b)
90 cm

49.

50.

cbse 12th Standard Physics Ray Optics and Optical Instruments Important Questions And Answers Study Material - QB365 Set E

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Std: 12th Standard CBSE - Physics

chapter: Ray Optics and Optical Instruments - Important Questions And Answers

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Questions:

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Answers Key:

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