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 6 of 12 pages

Question 51. In a Young’s double slit experiment, the distance between the slits is 0.2 mm and the distance of the screen from the slits is 2 m. If light of wavelength 500 nm is used, find the number of fringes formed between two points separated by 1 cm on the screen.

Discuss Question

Answer: Option B. -> 2
:
B

y = n β

Here

β = \frac{λ D}{d} = 0.5 c m

2 fringes.

Question 52. In a certain double slit experimental arrangement interference fringes of width 1.0 mm each are observed when light of wavelength 5000 is used. Keeping the set up unaltered, if the source is replaced by another source of wavelength 6000 , the fringe width will be
[CPMT 1988]

0.5 mm
1.0 mm
1.2 mm
1.5 mm

Discuss Question

Answer: Option C. -> 1.2 mm
:
C

Question 53. The intensities of two light sources are I and 9I respectively. If the phase difference between the waves emitted by them is

π

, then the resultant intensity at the point of observation will be

Discuss Question

Answer: Option B. -> 4I
:
B

I = I_{1} + I_{2} + 2 \sqrt{I_{1} I_{2}} c o s ϕ = 4 I

Question 54. In Young's double slit experiment the phase difference between the waves reaching the central fringe and fourth dark fringe will be

zero
4π
6π
7π

Discuss Question

Answer: Option D. -> 7π
:
D

Δ ϕ = (2 n - 1) π; n = 4

= (2 \times 4 - 1) π

= (8 - 1) π

Δ ϕ = 7 π

Question 55. The fringe width changes from 0.24 mm to 0.3 mm when the screen is moved by 20 cm away from the slits separated by 2 mm. calculate the wavelength of light used.

400 nm
500 nm
600 nm
700 nm

Discuss Question

Answer: Option C. -> 600 nm
:
C

β_{1} = \frac{λ D}{d}, β_{2} = \frac{λ (D + 0.20)}{d}

\Rightarrow D = 0.8 m

β = \frac{λ D}{d}

;

λ = 600 n m

Question 56. A double convex lens, lens made of a material of refractive index

μ_{1}

is placed inside two liquids or refractive indices

μ_{2}

and

μ_{3}

, as shown

μ_{2} > μ_{1} > μ_{3}

. A wide, parallel beam of light is incident on the lens from the left.
$A Double Convex Lens, Lens Made Of A Material Of Refractive ...$

A single convergent beam
Two different convergent beams
Two different divergent beams
A convergent and a divergent beam

Discuss Question

Answer: Option D. -> A convergent and a divergent beam
:
D
As

μ_{2} > μ_{1}

,the upper half of the lens will become diverging.
As

μ_{1} > μ_{3}

,the lower half of the lens will become converging

Question 57. 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

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

Angle of refraction

= ∠ r

Angle of incidence is equal to angle of reflection [law of reflection]

∴

Angle of reflection

= 60^{\circ}

Given that reflected and refracted ray are perpendicular.
From figure

60^{\circ} + 90^{\circ} + ∠ r = 180^{\circ}

[angle sum property]

∠ r = 30^{\circ}

∠ i = 60^{\circ}, ∠ r = 30^{\circ}

μ = \frac{s i n 60}{s i n 30} = \sqrt{3}

Question 58. The refractive index of a piece of transparent quartz is the greatest for
[MP PET 1985, 94]

Red light
Violet light
Green light
Yellow light

Discuss Question

Answer: Option B. -> Violet light
:
B
$The Refractive Index Of A Piece Of Transparent Quartz Is The...$

Question 59. The ratio of the refractive index of red light to blue light in air is
[CPMT 1978]

Less than unity
Equal to unity
Greater than unity
Less as well as greater than unity depending upon the experimental arrangement

Discuss Question

Answer: Option A. -> Less than unity
:
A
$The Ratio Of The Refractive Index Of Red Light To Blue Light...$

Question 60. When light is incident on a medium at angle i and refracted into a second medium at an angle r, the graph of sin i vs sinr is as shown in the graph. From this, one can conclude that
$When Light Is Incident On A Medium At Angle I And Refracted ...$

Velocity of light in the second medium is 1.73 times the velocity of light in the I medium
Velocity of light in the I medium is 1.73 times the velocity in the II medium

Discuss Question

Answer: Option B. -> Velocity of light in the I medium is 1.73 times the velocity in the II medium
:
B
$When Light Is Incident On A Medium At Angle I And Refracted ...$