CBSE Class 12 Physics Wave Optics MCQs

Question : Wavefront is the locus of all points, where the particles of the medium vibrate with the same
(a) phase
(b) amplitude
(c) frequency
(d) period
Answer: A

Question : A plane wave passes through a convex lens. The geometrical shape of the wavefront that emerges is
(a) plane
(b) diverging spherical
(c) converging spherical
(d) None of these
Answer: C

Question : Huygen’s concept of secondary wave
(a) allows us to find the focal length of a thick lens
(b) is a geometrical method to find a wavefront
(c) is used to determine the velocity of light
(d) is used to explain polarisation
Answer: B

Question : The interfering fringes formed by a thin oil film on water are seen in yellow light of sodium lamp. We find the fringes
(a) coloured
(b) black and white
(c) yellow and black
(d) coloured without yellow
Answer: A

Question : Two coherent sources of intensity ratio 1 : 4 produce an interference pattern. The fringe visibility will be
(a) 1
(b) 0.8
(c) 0.4
(d) 0.6
Answer: B

Question : The fringe width in a Young’s double slit experiment can be increased if we decrease
(a) width of slits
(b) separation of slits
(c) wavelength of light used
(d) distance between slits and screen
Answer: B

Question : If Young’s double slit experiment is performed in water keeping the rest of the set-up same, the fringes will
(a) increase in width
(b) decrease in width
(c) remain unchanged
(d) not be formed
Answer: B

Question : The maximum number of possible interference maxima for slit-separation equal to twice the wavelength in Young’s double-slit experiment is
(a) three
(b) five
(c) infinite
(d) zero
Answer: B

Question : In the Young’s Double slit experiment, when we place a converging lens after the slits and place the screen at the focus of the lens, it
(a) introduces an extra path difference in the parallel beam.
(b) introduces no path difference in the parallel beam.
(c) introduces an extra phase difference in the parallel beam.
(d) introduces an extra fringe in the diffraction pattern.
Answer: B

Question : Distance between screen and source is decreased by 25%. Then the percentage change in fringe width is
(a) 20%
(b) 31%
(c) 75%
(d) 25%
Answer: D 

Question : Light of wavelength 6.5 × 10^–7 m is made incident on two slits 1 mm apart. The distance between third dark fringe and fifth bright fringe on a screen distant 1 m from the slits will be
(a) 0.325 mm
(b) 0.65 mm
(c) 1.625 mm
(d) 3.25 mm
Answer: C

Question : In Young’s double slit expt. the distance between two sources is 0.1 mm. The distance of the screen from the source is 20 cm. Wavelength of light used is 5460 Å. The angular position of the first dark fringe is
(a) 0.08°
(b) 0.16º
(c) 0.20º
(d) 0.32º
Answer: B

Question : The separation between successive fringes in a double slit arrangement is x. If the whole arrangement is dipped under water what will be the new fringe separation? [The wavelenght of light being used is 5000 Å]
(a) 1.5 x
(b) x
(c) 0.75 x
(d) 2 x
Answer: C

Question : If the width of the slit in single slit diffraction experiment is doubled, then the central maximum of diffraction pattern becomes
(a) broader and brighter
(b) sharper and brighter
(c) sharper and fainter
(d) broader adn fainter.
Answer: B

Question : When monochromatic light is replaced by white light in Fresnel’s biprism arrangement, the central fringe is
(a) coloured
(b) white
(c) dark
(d) None of these
Answer: B

Question : Light transmitted by nicol prism is
(a) unpolarised
(b) plane polarised
(c) circularly polarised
(d) elliptically polarised
Answer: B

Question : Optically active substances are those substances which
(a) produces polarised light
(b) produces double refraction
(c) rotate the plane of polarisation of polarised light
(d) converts a plane polarised light into circularly polarised light.
Answer: C

Question : The condition for observing Fraunhoffer diffraction from a single slit is that the light wavefront incident on the slit should be
(a) spherical
(b) cylindrical
(c) plane
(d) elliptical
Answer: C

Question : When ordinary light is made incident on a quarter wave plate, the emergent light is
(a) linearly polarised
(b) circulary polarised
(c) unpolarised
(d) elliptically polarised
Answer: D

Question : In the propagation of light waves, the angle between the plane of vibration and plane of polarisaiton is
(a) 0º
(b) 90º
(c) 45º
(d) 80º
Answer: B