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 8 of 12 pages

Question 71. A plane mirror is placed at origin parallel of y- axis, facing the positive x–axis. An object starts from (2m, 0, 0) with a velocity of

(2^i + 2^j

), relative velocity of image with respect to object is along

Positive x – axis
Negative x-axis
Positive y-axis
Negative y-axis

Discuss Question

Answer: Option B. -> Negative x-axis
:
B

A Plane Mirror Is Placed At Origin Parallel Of Y- Axis, Faci...

| {⃗ v}_{0} | = | {⃗ v}_{1} |

= \sqrt{(2)^{2} + (2)^{2}}

= 2 \sqrt{2}

m/s
Relative velocity of image with respect to object is in negative x-direction as shown in figure.

Question 72. Finger prints on a piece of paper may be detected by sprinkling fluorescent
powder on the paper and then looking it into [MP PET/PMT 1988]

Mercury light
Sunlight
Infrared light
Ultraviolet light

Discuss Question

Answer: Option D. -> Ultraviolet light
:
D
Ultraviolet light

Question 73. If an object is placed asymmetrically between two plane mirrors, inclined at

60^{\circ}

, the total number of images formed is

5
4
2
infinite

Discuss Question

Answer: Option A. -> 5
:
A

\frac{360}{θ} = \frac{360}{60} = 6

even number
No. of image

n = \frac{360}{θ} - 1

=6-1
n =5

Question 74. Finger prints on a piece of paper may be detected by sprinkling fluorescent
powder on the paper and then looking it into [MP PET/PMT 1988]

Mercury light
Sunlight
Infrared light
Ultraviolet light

Discuss Question

Answer: Option D. -> Ultraviolet light
:
D
Ultraviolet light

Question 75. A plane mirror and a person are moving towards each other with same velocity v. Then the velocity of the image is

Discuss Question

Answer: Option C. -> 3v
:
C
If mirror would be at rest, then velocity of image should be 2v. but due to the motion of mirror, velocity of image will be 2v + v = 3v.

Question 76. What should be the angle between two plane mirrors so that whatever be the angle of incidence, the incident ray and the reflected ray from the two mirrors be parallel to each other

60∘
90∘
120∘
175∘

Discuss Question

Answer: Option B. -> 90∘
:
B
Incident ray and finally reflected ray are parallel to each other means

δ = 180^{\circ}

What Should Be The Angle Between Two Plane Mirrors So That W...

From

δ = 360 - 2 θ \Rightarrow 180 = 360 - 2 θ \Rightarrow θ = 90^{\circ}

Question 77. A thick plane mirror shows a number of images of the filament of an electric bulb. Of these, the brightest image is the

First
Second
Fourth
Last

Discuss Question

Answer: Option B. -> Second
:
B

A Thick Plane Mirror Shows A Number Of Images Of The Filamen...

Question 78. A small plane mirror placed at the centre of a spherical screen of radius R. A beam of light is falling on the mirror. If the mirror makes n revolution. per second, the speed of light on the screen after reflection from the mirror will be

4πnR
2πnR
nR2π
nR4π

Discuss Question

Answer: Option A. -> 4πnR
:
A
When plane mirror rotates through an angleθ, the reflected ray rotates through an angle 2θ. So spot on the screen will make 2nrevolution per second.

Question 79. A plane mirror is approaching you at a speed of 10 cm/sec You can see your image in it. At what speed will your image approach you

10 cm/sec
5 cm/sec
20 cm/sec
15 cm/sec

Discuss Question

Answer: Option C. -> 20 cm/sec
:
C
Suppose at any instant, plane mirror lies at a distance x from object. Image will be formed behind the mirror at the same distance x.

A Plane Mirror Is Approaching You At A Speed Of 10 Cm/sec Y...

When the mirror shifts towards the object by distance ‘y’ the image shifts =x + y -(x-y) =2ySo speed of image = 2 ´ speed of mirror

Question 80. A watch shows time as 3 : 25 when seen through a mirror, time appeared will be

8 : 35
9 : 35
7 : 35
8 : 25

Discuss Question

Answer: Option A. -> 8 : 35
:
A
For solving this type of problems remember
Actual time = 11 : 60 - given time
So here Actual time = 11 : 60 - 3 : 25 = 8 : 35