Wave Optics

Wave Optics Class 12 Physics MCQs

1. The idea of secondary wavelets for the. propagation of a wave was first given by
(a) Newton
(b) Huygens
(c) Maxwell
(d) Fresnel

2. Light propagates rectilinearly, due to
(a) wave nature
(b) wavelengths
(c) velocity
(d) frequency

3. Which of the following is correct for light diverging from a point source?
(a) The intensity decreases in proportion with the distance squared.
(b) The wavefront is parabolic.
(c) The intensity at the wavelength does not depend on the distance.
(d) None of these.

4. The refractive index of glass is 1.5 for light waves of X = 6000 A in vacuum. Its wavelength in glass is
(a) 2000 Å
(b) 4000 Å
(c) 1000 Å
(d) 3000 Å

5. The phenomena which is not explained by Huygen’s construction of wavefront
(a) reflection
(b) diffraction
(c) refraction
(d) origin of spectra

6. A laser beam is used for locating distant objects because
(a) it is monochromatic
(b) it is not chromatic
(c) it is not observed
(d) it has small angular spread.

7. Two slits in Young’s double slit experiment have widths in the ratio 81 :1. The ratio of the amplitudes of light waves is
(a) 3 :1
(b) 3 : 2
(c) 9 :1
(d) 6:1

8. When interference of light takes place
(a) energy is created in the region of maximum intensity
(b) energy is destroyed in the region of maximum intensity
(c) conservation of energy holds good and energy is redistributed
(d) conservation of energy does not hold good

9. In a double slit interference pattern, the first maxima for infrared light would be
(a) at the same place as the first maxima for green light
(b) closer to the centre than the first maxima for green light
(c) farther from the centre than the first maxima for green light
(d) infrared light does not produce an interference pattern

10. To observe diffraction, the size of the obstacle
(a) should beX/2, where X is the wavelength.
(b) should be of the order of wavelength.
(c) has no relation to wavelength.
(d) should be much larger than the wavelength.

11. The angular resolution of a 10 cm diameter telescope at a wavelength of 5000 A is of the order of
(a) 10⁶ rad
(b) 10^-2 rad
(c) 10^-4 rad
(d) 10^-6 rad

12. The velocity of light in air is 3 * 108 ms-1 and that in water is 2.2 * 108 ms” . The polarising angle of incidence is
(a) 45°
(b) 50°
(c) 53.74°
(d) 63

13. An optically active compound
(a) rotates the plane of polarised light
(b) changes the direction of polarised light
(c) does not allow plane polarised light to pass through
(d) none of these

Question 14.
What happens if one of the slits, say S₁ in Young’s double , slit experiment-is covered with a glass plate which absorbs half the intensity of light from it?
(a) The bright fringes become less-bright and the dark fringes have a finite light intensity
(b) The bright fringes become brighter and the dark fringes become darker
(c) The fringe width decreases
(d) No fringes will be observed

Question 15.
What happens to the interference pattern the two slits S₁ and S₂ in Young’s double experiment are illuminated by two independent but identical sources?
(a) The intensity of the bright fringes doubled
(b) The intensity of the bright fringes becomes four times
(c) Two sets of interference fringes overlap
(d) No interference pattern is observed

Question 16.
What is the reason for your answer to the above question?
(a) The two sources do not emit light of the same wavelength
(b) The two sources emit waves which travel with different speeds
(c) The two sources emit light waves of different amplitudes
(d) There is not constant phase difference between the waves emitted by the two sources

Question 17.
A single slit diffraction pattern is obtained using a beam of red light What happened the red light is replaced by the blue light?
(a) There is no change in diffraction pattern
(b) Diffraction fringes become narrower and crowded
(d) Diffraction fringes become broader and farther apart
(d) The diffraction pattern disappear

Question 18.
When a polaroid is rotated, the intensity of light varies but never reduces to zero. It shows that the incident light is:
(a) unpolarised
(b) completely plane polarised
(c) partially plane polarised
(d) None of the above

Question 19.
When a polaroid is rotated, the intensity of light does not vary. The incident light may be:
(a) unpolarised
(b) completely polarised
(c) partially plane polarised
(d) None of the above

Question 20.
In Young’s double slit experiment, a maximum is obtained when the path difference between the interfering waves is (n ∈ l):
(a) nλ
(b) n \(\frac{λ}{2}\)
(c) (2n + 1) \(\frac{λ}{2}\)
(d) (2n – 1) \(\frac{λ}{4}\)

Question 21.
For sustained interference, we need two sources which
emit radiations :
(a) of the same intensity
(b) of the same amplitude
(c) having a constant phase difference
(d) None of these

Question 22.
Two sources of light are said to be coherent when both give out light waves of the same:
(a) amplitude and phase
(b) intensity and wavelength
(c) speed
(d) wavelength and a constant phase difference

Question 23.
The intensity of light emerging from the two slits, in Young’s experiment is in the ratio 1 : 4. The ratio of,the intensity of the minimum to that of the consecutive maximum will be:
(a) 1 : 4
(b) 1 : 9
(c) 1 : 16
(d) 2 : 3

Question 24.
Poisson’s bright spot was discovered by:
(a) Fresnel
(b) Rayleigh
(c) Poisson
(d) Fraunhoffer

Question 25.
The theory of expanding universe is confirmed by the observation of the spectral lines of the star, which shows :
(a) green shift
(b) red shift
(c) violet shift
(d) yellow shift

Question 26.
The application of Doppler effect are:
(a) Doppler spectrometer
(b) Doppler radius
(c) Doppler velocimeter
(d) All of these

Question 27.
Which of the following is conserved when light waves interefere?
(a) phase
(b) intensity
(c) amplitude
(d) none of these

Question 28.
In Young double slit experiment, a minimum is obtained when the phase difference of the superposing waves, is (n ∈ l):
(a) nπ
(b) (n + \(\frac{1}{2}\))π
(c) (2n + 1)π
(d) zero

Question 29.
The angle of minimum deviation of a prism depends upon the aggie of:
(a) incidence
(b) reflection
(c) prism
(d) none of these

Question 30.
he minimum value of the refractive index is:
(a) zero
(b) 1
(c) less than 1 but not zero
(d) more than 1

Question 31.
Polarization of light prove the :
(a) corpuscular nature of light
(b) quantum nature of light
(c) Transverse wave nature of light
(d) Longitudinal wave nature of light

Question 32.
Out of the following Statements which is not correct?
(a) When unpolarised light passes through Nicol’s prism, the emergent light is elliptically polarized
(b) Nicol’s prism works on the principle of double refraction and T.l.R.
(c) Nicol’s prism can be used both the produce and analyse polarized light
(d) Calcite and Quartz are both double refracting crystal

Question 33.
Polaroid glasses is used in sun glasses because :
(a) It reduces the light intensity to half on account of polarization
(b) It is fashionable
(c) It has good colour
(d) It is cheaper

Question 34.
In vacuum, the speed of light depends upon :
(a) frequency
(b) velocity
(c) wave length
(d) None of these

Question 35.
The fringe width (β) of a diffraction pattern and the slit width d are related as:
(a) β ∝ d
(b) β ∝\(\frac{1}{d}\)
(c) β ∝ √d
(d) β ∝ \(\frac{1}{d^2}\)

Question 36.
C.V. Raman was awarded the Nobel prize for his work associated with which of the following phenomenon of radiations?
(a) scattering
(b) diffraction
(c) interference
(d) polarisation

Question 37.
Light takes 10^-10 to cross a glass slab. What is the thickness of the glass slab?
(a) 2 cm
(b) 3 cm
(c) 2.5 cm
(d) 3.5 cm

Question 38.
In Young’s double slit experiment, the central point on the screen is:
(a) bright
(b) dark
(c) first bright and later dark
(d) first dark and later bright

Question 39.
Between the slit is id\ the distance between the slit and the screen is α, with light of wavelength λ, the number of fringe observed per metre on the screen is:
(a) \(\frac{δy}{α}\)
(b) \(\frac{Dα}{λ}\)
(c) \(\frac{α}{Dλ}\)
(d) \(\frac{λd}{D}\)

Question 40.
In Young’s double slit experiment the distance between the slit and the screen is doubled and the separation between the slit is reduced to half. The fringe width:
(a) is doubled
(b) become four time
(c) is halfed
(d) remain unchanged

Question 41.
In a Young’s double slit experiment the distance between the slit is 1 mm and the distance of screen from the slit is 1 m. If light of wavelength 6000 A is used then the fringe width is:
(a) 0.4 mm
(b) 0.5 mm
(c) 0.6 mm
(d) 0.8 mm

Question 42.
A person cannot see object clearly beyond 50 cm. The pow er of the lens to correct his vision is :
(a) +0.5 dioptre
(b) -0.5 dioptre
(c) -2 dioptre
(d) +2 dioptre

Question 43.
A phase difference of 5π corresponds to a path difference (in terms of λ) of:
(a) 5λ
(b) 10λ.
(c) 5λ/2
(d) 2λ

Question 44.
A polaroid produces a strong beam of light which is :
(a) circularly polarised
(b) elliptically polarised
(c) plane polarised
(d) unpolarised

Question 45.
Images of a distant lamp seen through a fire cloth rotate on rotating the cloth. This is due to the phenomenon of:
(a) interference
(b) diffraction
(c) polarisation
(d) scattering

Question 46.
A young’s double slit experiment uses a monochromatic source. The shape of interference fringes formed on a screen is :
(a) parabola
(b) straight line
(c) circle
(d) hyperbola

Question 47.
A monochromatic light is refracted from air into a glass of refractive index µ. The ratio of the wavelengths of the incident and the refracted waves is:
(a) 1 : µ
(b) 1 : µ²
(c) µ : 1
(d) µ² : 1

Question 48.
The focal length of the lens is 50 cm; then its power is:
(a) +2D
(b) +1D
(c) -2D
(d) -1D

Question 49.
In the above question, the number of the lens is:
(a) +2
(b) +1
(c) -2
(d) -1

Question 50.
The refractive index of diamond is about:
(a) 1
(b) 1.42
(c) 2.42
(d) 4.24

Question 51.
Two lenses having power +6 D and -4 D are placed in contact. The power of the combination is
(a) -2D
(b) -4D
(c) +4D
(d) +2 D

Question 52.
Diffraction was discovered by :
(a) Grimaldi
(b) Thomas Young
(c) Malus
(d) Huygens

Question 53.
The electromagnetic wave theory of light fails to explain :
(a) compton effect
(b) photoelectric effect
(c) neither (a) nor (b)
(d) Both (a) and (b)