# NCERT Class 12 Physics Chapter 9 Optics Important Questions for Board Exams with Answers

## Designed by expert teachers from latest edition of NCERT books to get good marks in board exams.

#### Here we have given Important Questions For Class 12 Physics

51. For giving colour to the sky in the day time, the Sun rays are
(a) diffused
(b) scattered
(c) refracted
(d) reflected.

1. Due to atmospheric refraction the effect on sunrise and sunset is
(a) sun rise early, sun set late
(b) sun rise late, sun set early
(c) both take place early.
(d) both take place in late.
2. Size of an object depends on
(a) objecte angle
(b)image angle
(c) virtual angle
(d) critical angle
3. A convex mirror gives image which are real and erect.
(a) real and inverted.
(b)real and erect.
(c) virtual and erect
(d) virtual and inverted.
4. An object is placed between two plane mirrors
inclined at an angle of 45 The number of images will be

(b) 7
(a) 12
(d) none of these.
(c) 4

56.A man is approaching towards a mirror at the rate 10 m/sec. The image approaches him at the rate of
(b) 20 m/sec
(a) 10 m/sec
(d) none
(C) zero

1. A ray of light is incident on a plane mirror at the
angle of 45°, the deviation produced by the mirror is

(b) 90
(a) 45
(d)135
(c) 60
2. For a real object, which of the following can
produce real image

(b) Concave lens
(a) Plane mirror
(c) Convex mirror
(d) Concave mirror.
3. If the focal length of the lens is 10 cm, the power
of lens is

(a) 1D
(d) OD
(c) 100D
(b)10D
4. During refraction which properties of light
remains constant ?
(a) Velocity
(b) Frequency
(d) None.
(c) Wave length
5. A double convex air bubble, in water, will act like
(a) converging lens
(b) diverging lens
(c) both (a) and (b)
(d) none of these.
6. The focal length of a lens whose power is 2D Is
(a)1/50
(b)2
(c) 20
(d) 50 cm
7. When monochromatic light travels from are
glass, then
(a) frequency decreases
(b) frequency increases
(C) wavelength decreases
(d)wavelength increàses
8. If critical angle is 45°, the R.I. will be
(a) 1.5
(b) 1.3
(c) 1.1
d) 2
9. The wave theory of light was given by
(b) Fresnel
(c) Huygen
(d) Young.
(a) Newton
10. wavefront from a distant light source at infinity is
(a) spherical
(b) plane mirrors
(c) cylindrical
(d) circular.
11. Wavefront from a near point light source is
(a) spherical
(b) plane
(c) cylindrical
(d) circular.

68.Normals to wavefront are called
(a) tangents
(b) pencils
(c) beams
(d) rays.

69.Rays associated with a plane wavefront are
(a) converging
(b) diverging
(C)parallel
(d)none.

70.For constructive interference the path difference
should be.

(a) 2n
(b) (2n+1)
(c)(2n-1)y/2
(d) none

1. For destructive interference the path difference
should be

(a) 2n.
(6)(2n+1)
(C)(2n-1)
(d) none.
2. For constructive interference, the phase
difference should be

(a) 2nt
(b) (2n+1
(c) 10t
(d) none.
3. For destructive interference, the phase difference
should be
(a) 2n7t
(b) (2n+ 1t
(c) 107t
(d) none
4. phase reversal takes place in case of reflection
from
(a) rarer to rarer medium
(6) rarer to denser medium
(c) denser to denser medium.
5. If intens ratio is 4:1. Then the ratio 1max/1max will be.
(a) 4:1
(b) 1:4
(d)1:9
(c) 9:1
6. In above question if Imax/Imax =4/1 then ratio of slit min width will be
(a) 1:2O
(b) 2:1op
(d) 3:1b
(c) 1:3
7. In a certain case, the maxima and minima are
equally bright and width. The pattern is due to

(a) diffraction
(b)interference
(c) polaisation
(d) refraction.

78.The R.I. of glass is minimum for light of which
colour?

(a) Red
(b) Blue
(c) Yellow
(d)None.

1. The formation of rainbow is an example of
(a) reflection of light
(b) dispersion of light.
(c) interference of light.
(d) diffraction of light.
2. A monochromatic light passed through a prism
shows minimum deviation for which colour ?

(a) Red
(b)Violet
(d)Green
(c) Yellow
3. R.I. of a prism of angle 60° and d is 30°
(a)√2
(b) 1/√2
(d)3
(c) 1
4. The angular magnification of a simple microscope
can be increased by increasing

(a) focal length of lens
(b) size of object.
(c) aperture of lens
(d) power of lens.
5. The least distance of distinct vision is
(a) 10 cm
(b)15 cm
(c) 25 cm
(d)none.
6. A person can not see objects clearly beyond 50
cm. The power of the lens to correct the vision is

(a) +5D
(b)-0.5D
(c)-2D
(d)2D
7. The intensity ratio is 25: 9. Then ratio of the intensities of maxima and minima is
(a) 64:4
(b)34: 16
(c) 25:9
(d) 8:2
8. In Young’s double slit experiment the distance
between the slits is gradually increased. The width of fringe system

(a) increase
(b) decreases
(c is constant
(d) none
9. The coherence of two light sources means that
the light waves emitted have
(a) same frequency
(b) same intensity
(d) same velocity
(c)same phase
10. Frequency of a wave is 6 x 10SHz. The wave is
(b) microwave
(d)UV
(c) x-ray
11. The theory associated with secondary wavelet is
(a) Doppler’s effect
(b) Special theory of relativity.o
(c) Huygen’s wave theory
(d) None of these.
12. A real, inverted and equal in size image can be formed by a
(a) convex mirror
(b)plane mirror
(c) concave mirror
(d) none of these
13. Magnification of a concave mirror is image is o
(a) real and magnifield
(b) erect and magnifield
(c) virtual and diminishedl o 1
(d) real and diminished.

92.An object is placed between two parallel plane mirrors. The number of images formed is
(b) four
(a) infinite
(d) one
(c) two

93.Angle between two plane mirror is 30°. The maximum number of images of an object placed in between them is
(a) 11 0
(b) 12 e
(d) 13
(c) 10won

1. The deviations produced by a prism is E8
(a) same for all wávelengths.
(b) greatest for red least for violet
(c)greatest for violet, least for red.
(d) greatest for for yellow,wog oilf
2. The refractive index of water and glass are
and Then critical angle when light moves from glass to water is

(a) sin–⁴(4/3)
(b) sin–(5/3)
(c)sin–(4/5)
(d)sin –1(5/4)
3. . The cirtical angle is 30°. en velocity of lightin
the medium is
(a) 3x 10 m/s
(b) 1.5 x 10″ m/s
(c) 6x 10 m/s
(d) 2x 10″ m/s
4. A transparent material is completly invisible i An
vacuum. Then R.I. is

(c)<1 3
(b) 1
(a) 1
(d) 1.33
5. The image formed by concave lens is
(b) always virtual
(a) always real
(d) always enlarged
(c) always inverted
6. Focal length of a convex lens is f’. What is the
minimum distance between an object and its real
image ?

(a) 4f9t(d
(b) 2fR
(c) 3f3G
(d) f
7. An object is placed at a distance of f/2 from a
convex lens. The image will form ola

(a) at f
(6) at 2f
(c) at one of its foci
(d) at
8. The power of convex lens of focal length 20 cm
IS
9. The power of lens is 2 rad/m. What is the focal length ?
(b) beyond 50 cm
(a) 50 cm
(d)none of these
(c) within 50 cm
10. Two light sources are coherent when
(a) their amplitudes are equal
(b) their frequencies are equal 1ib
(c) their wavelengths are equal.
(d) their phase difference is constant
11. Ratio of intensities of two wave is given by
4:1.The ratio of the amplitudes of the wave is

(b) 1:2
(a) 2:1 d
(d) 1:4
(c) 4:1on
12. The wave-length of light used in Youngs
experiment is increased. Then fringe width will

uits b) decrease
(a) increase
(d) none of these.
(c) constant
13. In Young’s double slit experiment d is halved and Dis doubled. Then fringe width will be
(b) halved
(a) unchanged
(c doubled

107.Light is
(a) mechanical wave
(b)Non-mechanical wave
(c) Both (a) and (b)
(d) None of these

1O8. During reflection and refraction which properties
of light remains constant ?o
(a) Frequency
(b) Wavelength
(c) Amplitude
(d) velocity

1. Interference obeys principle of conservation of

(a) Energy
(b) Mass
(C) Charge
(d) None of these

110.Optical fibre works on which principle ?
(a) Reflection
(b) Refraction
(c) Total internal reflection
(d) None of these