Optics(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

OPTICS MCQs

Wave Optics, Ray Optics Refraction, Ray Optics Fundamentals, Ray Optics Curved Surface Refraction, Ray Optics Curved Mirrors

Total Questions : 111 | Page 7 of 12 pages

Question 61. Refractive index for a material for infrared light is

[CPMT 1984]

Equal to that of ultraviolet light
Less than for ultraviolet light
Equal to that for red colour of light
Greater than that for ultraviolet light

Discuss Question

Answer: Option B. -> Less than for ultraviolet light
:
B
$Refractive Index For A Material For Infrared Light Is [CPMT...$

Question 62. If

ε_{0}

and

μ_{0}

are respectively, the electric permittivity and magnetic permeability of free space,

ε

and

μ

the corresponding quantities in a medium, the refractive index of the medium is

√μ∈μ0∈0
√μ∈μ0∈0
√μ0∈0μ∈
√μμ0∈∈0

Discuss Question

Answer: Option B. -> √μ∈μ0∈0
:
B

R . I = \frac{C_{0}}{C} = \sqrt{\frac{μ \in}{μ_{0} \in_{0}}} =

Question 63. In the adjoining diagram, a wavefront AB, moving in air is incident on a plane glass surface XY. Its position CD after refraction through a glass slab is shown also along with the normals drawn at A and D. The refractive index of glass with respect to air (μ=1 ) will be equal to

sin θsin θ′
sin θsin ϕ′
sin ϕ′sin θ
ABCD

Discuss Question

Answer: Option B. -> sin θsin ϕ′
:
B
in the case of refraction is CD is the refracted waves front and

V_{1}

and

V_{2}

are the speed of light in
the two media, then in the time the wavelets from B reaches C, the wavelets from A will reach D,
such that

t = \frac{B C}{v_{a}} = \frac{A D}{v_{g}} \Rightarrow \frac{B C}{A D} = \frac{v_{a}}{v_{g}} . . . (i)

But in

△ A C B, B C = A C s i n θ . . . (i i)

While in

△ A C D, A D = A C s i n ϕ^{'} . . . (i i i)

From equations (i), (ii) and (iii)

\frac{v_{a}}{v_{g}} = \frac{s i n θ}{s i n ϕ^{'}}

Also

μ \propto \frac{1}{v} \Rightarrow \frac{v_{a}}{v_{g}} = \frac{μ_{g}}{μ_{a}} = \frac{s i n θ}{s i n ϕ^{'}} \Rightarrow μ_{g} = \frac{s i n θ}{s i n ϕ^{'}}

Question 64. On a glass plate a light wave is incident at an angle of

60^{\circ}

. If the reflected and the refracted waves are mutually perpendicular, the refractive index of material is

√32
√3
32
1√3

Discuss Question

Answer: Option B. -> √3
:
B
From figure

r = 30^{\circ}

∴ μ = \frac{s i n i}{s i n r} = \frac{s i n 60^{\circ}}{s i n 30^{\circ}} = \sqrt{3}

On A Glass Plate A Light Wave Is Incident At An Angle Of 60�...

Question 65. When a plane mirror is placed horizontally on a level ground at a distance of 60m from the foot of a tower, the top of the tower and its image in the mirror subtend an angle of

at the eye. The height of the tower will b
[CPMT 1984]

30m
60m
90m
120m

Discuss Question

Answer: Option B. -> 60m
:
B

When A Plane Mirror Is Placed Horizontally On A Level Ground...

Question 66. Two plane mirrors. A and B are aligned parallel to each other, as shown in
the figure. A light ray is incident at an angle of 30⁰ 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

[IIT-JEE (Screening) 2002]

Discuss Question

Answer: Option B. -> 30
:
B
From the following ray diagram

Question 67. It is desired to photograph the image of an object placed at a distance of 3 m from the plane mirror. The camera which is at a distance of 4.5 m from the mirror should be focussed for a distance of

6m
4.5m
6m
7.5m

Discuss Question

Answer: Option D. -> 7.5m
:
D

It Is Desired To Photograph The Image Of An Object Placed At...

Question 68. A light bulb is placed between two plane mirrors inclined at an angle of

60^{\circ}

.The number of images formed are

Discuss Question

Answer: Option C. -> 5
:
C
number of images

= (\frac{360}{θ} - 1) = (\frac{360}{60} - 1) = 5

Question 69. A man is 180 cm tall and his eyes are 10cm below the top of his head. In order to see his entire height right from toe to head, he uses a plane mirror kept at a distance of 1mfrom him. The minimum length of the plane mirror required is

[MP PMT 1993; DPMT 2001]

180cm
90cm
85cm
170cm

Discuss Question

Answer: Option B. -> 90cm
:
B

A Man Is 180 Cm tall And His Eyes Are 10cm below The Top O...

Question 70. A ray of light incident on the first mirror parallel to the second and is reflected from the second mirror parallel to first mirror. The angle between two mirrors is