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 11 of 12 pages

Question 101. The graph shows how the magnification m produced by a convex thin lens varies with image distance v. What was the focal length of the used
[DPMT 1995]

Discuss Question

Answer: Option A. ->
:
D

The Graph Shows How The Magnification M Produced By A Convex...

Question 102. The object distance u, the image distance v and the magnification m in a lens follow certain linear relations. These are

1u versus 1v
m versus u
u versus v
m versus 1u

Discuss Question

Answer: Option A. -> 1u versus 1v
:
A
For a lens

\frac{1}{f} = \frac{1}{v} - \frac{1}{u} \Rightarrow \frac{1}{v} = \frac{1}{u} + \frac{1}{f} . . . . (i)

Also

m = \frac{f - v}{f} = 1 - \frac{v}{f} \Rightarrow m = (- \frac{1}{f}) v + 1 . . . (i i)

On comparing equations (i) and (ii) with y =mx +c.
It is clear that relationship between

\frac{1}{v} v s \frac{1}{u}

and m vs v is linear.

Question 103. A point object is placed at a distance of 25 cm from a convex lens of focal length 20 cm. If a glass slab of thickness t and refractive index 1.5 is inserted between the lens and the object the image is formed at infinity. The thickness t is

10 cm
5 cm
20 cm
15 cm

Discuss Question

Answer: Option D. -> 15 cm
:
D
Image will be formed at infinity if object is placed at focus of the lens i.e., at 20 cm from thelens. Hence,
Shift =

25 - 20 = (1 - \frac{1}{μ}) t

5 = (1 - \frac{1}{1.5}) t

t = \frac{5 \times 1.5}{0.5} = 15 c m

Question 104. An object 2.5 cm high is placed at a distance of 10 cm from a concave mirror of radius of curvature 30 cm The size of the image is

9.2 cm
10.5 cm
5.6 cm
7.5 cm

Discuss Question

Answer: Option D. -> 7.5 cm
:
D

R = - 30 c m \Rightarrow f = - 15 c m

O = +2.5 cm, u =-10 cm
By mirror formula

\frac{1}{- 15} = \frac{1}{v} + \frac{1}{(- 10)} \Rightarrow v = 30 c m .

Also

\frac{I}{O} = - \frac{v}{u} \Rightarrow \frac{I}{(+ 2.5)} = - \frac{30}{(- 10)} \Rightarrow I = 7.5 c m

Question 105. A ray incident at an angle

53^{\circ}

on a prism and emerges at an angle of

37^{\circ}

as shown in figure. If the angle of incidence is made

50^{\circ}

then possible value of the angle of emergence is

A Ray Incident At An Angle 53∘ On A Prism And Emerges At A...

35∘
42∘
40∘
38∘

Discuss Question

Answer: Option D. -> 38∘
:
D
Deviation produce by the prism is

δ = i + e - A = 53^{\circ} + 37^{\circ} - A = 90^{\circ} - A

For angle of incidence

50^{\circ}

angle of emergence will be grater than

37^{\circ}

and also
i + e <

90^{\circ}

Question 106. An object of size 7.5cm is placed in front of a convex mirror of radius of curvature 25cm at a distance of 40cm The size of the image should be

2.3cm
1.78cm
1cm
0.8cm

Discuss Question

Answer: Option B. -> 1.78cm
:
B

Question 107. A concave mirror of focal length 15 cm forms an image having twice the linear dimensions of the object. The position of the object when the image is virtual will be

22.5 cm
7.5 cm
30 cm
45 cm

Discuss Question

Answer: Option B. -> 7.5 cm
:
B
f=-15 cm, m=+2(Positive because image is virtual)

∵ m = - \frac{v}{u} \Rightarrow v = - 2 u

By using mirror formula

\frac{1}{- 15} = \frac{1}{(- 2 u)} + \frac{1}{u} \Rightarrow u = - 7.5 c m

Question 108. A concave mirror of focal length 100 cm is used to obtain the image of the sun which subtends an angle of 30'. The diameter of the image of the sun will be

1.74 cm
0.87 cm
0.435 cm
100 cm

Discuss Question

Answer: Option B. -> 0.87 cm
:
B
Diameter of image of sun

d = f θ

\Rightarrow d = 100 \times (\frac{30}{60}) \times \frac{π}{180}

\Rightarrow d = 0.87 c m

A Concave Mirror Of Focal Length 100 Cm Is Used To Obtain Th...

Question 109. A point object is placed at a distance of 10 cm and its real image is formed at a distance of 20 cm from a concave mirror. If the object is moved by 0.1 cm towards the mirror, the image will shift by about