# CBSE Class 12 Physics Wave Optics MCQs

## MCQ for Class 12 Physics Wave Optics

Class 12 Physics students should refer to the following multiple-choice questions with answers for Wave Optics in standard 12. These MCQ questions with answers for Grade 12 Physics will come in exams and help you to score good marks

### Wave Optics MCQ Questions Class 12 Physics with Answers

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

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

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

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

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

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

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

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

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.

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%

Question : The locus of all particles in a medium, vibrating in the same phase is called
(a) wavelet
(b) fringe
(c) wave front
(d) None of these

Question : Which of the following is correct for light diverging from a point source?
(a) The intensity decreases in proportion for the distance squared.
(b) The wavefront is parabolic.
(c) The intensity at the wavelingth does depend of the distance.
(d) None of these.

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

Question : The phenomena which is not explained by Huygen’s construction of wavefront
(a) reflection
(b) diffraction
(c) refraction
(d) origin of spectr

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

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

Question : Spherical wavefronts, emanating from a point source,strike a plane reflecting surface. What will happen to these wave fronts, immediately after reflection?
(a) They will remain spherical with the same curvature,both in magnitude and sign.
(b) They will become plane wave fronts.
(c) They will remain spherical, with the same curvature, but sign of curvature reversed.
(d) They will remain spherical, but with different curvature, both in magnitude and sign.

Question : When light suffers reflection at the interface between water and glass, the change of phase in the reflected wave is
(a) zero
(b) π
(c) π/2
(d) 2π

Question : Two plane wavefronts of light, one incident on a thin convex lens and another on the refracting face of a thin prism. After refraction at them, the emerging wavefronts respectively become
(a) plane wavefront and plane wavefront
(b) plane wavefront and spherical wavefront
(c) spherical wavefront and plane wavefront
(d) spherical wavefront and spherical wavefront
(e) elliptical wavefront and spherical wavefront

Question : When a film is illuminated by white light, its upper portion appears dark. Path difference between two reflected beams at the spot must be
(a) zero
(b) λ/2
(c) 2 λ/2
(d) π

Question : From Brewster’s law of polarisation, it follows that the anlge of polarisaiton depends upon
(a) the wavelength of light
(b) plane of polarisation’s orientation
(c) plane of vibration’s orientation
(d) None of these

Question : If two sources are coherent, then the phase difference (Φ) between the waves produced by them at any point
(a) will change with time and we will have stable positions of maxima and minima.
(b) will not change with time and we have unstable positions of maxima and minima.
(c) Positions of will not change with time and we will have stable positions of maxima and minima.
(d) will change with time and we will have unstable positions of maxima and minima.

Question : The device which produces highly coherent sources is
(a) Fresnel biprism
(b) Young’s double-slit
(c) Laser
(d) Lloyd’s mirror

Question : Which of the following, cannot produce two coherent sources?
(a) Lloyd’s mirror
(b) Fresnel biprism
(c) Young’s double slit
(d) Prism

Question : Coherence is a measure of
(a) capability of producing interference by wave
(b) waves being diffracted
(c) waves being reflected
(d) waves being refracted

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

Question : Intensity of light depends on
(a) amplitude
(b) frequency
(c) wavelength
(d) velocity

Question : The colour of bright fringe nearest to central achromatic fringe in the interference pattern with white light will be
(a) violet
(b) red
(c) green
(d) yellow

Question : When unpolarised light is incident on a plane glass plate at Brewster’s angle, then which of the following statements is correct?
(a) Reflected and refracted rays are completely polarised with their planes of polarization parallel to each other
(b) Reflected and refracted rays are completely polarised with their planes of polarization perpendicular to each other
(c) Reflected light is plane polarised but transmitted light is partially polarised
(d) Reflected light is partially polarised but refracted light is plane polarised

Question : Laser light is considered to be coherent because it consists of
(a) many wavelengths
(b) uncoordinated wavelengths
(c) coordinated waves of exactly the same wavelength
(d) divergent beam

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

Question : In Young’s Double slit experiment, if the distance between the slit and screen (D) is comparable with fringe width (B), the fringe pattern on screen will
(a) strictly be a parabola
(b) strictly be a hyperbola
(c) be a elliptical
(d) be a straight line

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

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.

Question : The fringe width for red colours as compared to that for violet colour is approximately
(a) 3 times
(b) 2 times
(c) 4 times
(d) 8 times

Question : In Young’s double slit experiment, the minimum amplitude is obtained when the phase difference of super-imposing waves is (where n = 1, 2, 3, ...)
(a) zero
(b) (2 n – 1) π
(c) n π
(d) (n + 1) π

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

Question : In Young’s double slit experiment, one slit is covered with red filter and another slit is covered by green filter, then interference pattern will be
(a) red
(b) green
(c) yellow
(d) invisible

Question : Instead of using two slits, if we use two separate identical sodium lamps in Young’s experiment, which of the following will occur?
(a) General illumination
(b) Widely separate interference
(c) Very bright maxima
(d) Very dark minima

Question : Which of the following is not essential for two sources of light in Young’s double slit experiment to produce a sustained interference?
(a) Equal wavelength
(b) Equal intensity
(c) Constant phase relationship
(d) Equal frequency

Question : In Young's double slit experiment, the locus of the point P lying in a plane with a constant path difference between the two interfering waves is
(a) a hyperbola
(b) a straight line
(c) an ellipse
(d) a parabola

Question : If the width of the slit in single slit diffrection experiment is doubled, then the central maximum of diffraction pattern becomes
(b) sharper and brighter
(c) sharper and fainter

Question : A diffraction pattern is obtained by using beam of red. light what will happen, if red light is replced by the blue light?
(a) Bands disappear.
(b) Bands become broader and farther apart.
(c) No change will take place.
(d) Diffraction bands become narrow and crowded together.

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

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

Question : The phenomenon of diffraction can be treated as interference phenomenon if the number of coherent sources is
(a) one
(b) two
(c) zero
(d) infinity

Question : The diffraction effects in a microscopic specimen become important when the separation between two points is
(a) much greater than the wavelength of light used.
(b) much less than the wavelength of light used.
(c) comparable to the wavelength of light used.
(d) independent of the wavelength of light used.

Question : What is the Brewester angle for air to glass transition?( μag = 1.5)
(a) tan (1.5)
(b) sin (1.5)
(c) sin–1 (1.5)
(d) tan–1 (1.5)

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

Question : Transverse nature of light was confirmed by the phenomenon of
(a) refreaction of light
(b) diffraction of light
(c) dispersion of light
(d) polarization of light

Question : In the case of linearly polarized light, the magnitude of the electric field vector
(a) is parallel to the direction of propagation
(b) does not changes with time
(c) increases linearly with time
(d) varies periodically with time

Question : Unpolarized light is incident on a plane glass surface The angle of incidence so that reflected and refracted rays are perpendicular to each other, them
(a) tan iβ= μ/2
(b) tan iβ= μ
(c) sin iβ= μ
(d) cos iβ= μ

Question : Light waves can be polarised because they
(a) have high frequencies
(b) have short wavelength
(c) are transverse
(d) can be reflected

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

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.

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

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

Question : In the propagation of electromagnetic waves, the angle between the direction of propagation and plane of polarisation is
(a) 0º
(b) 45º
(c) 90º
(d) 180º

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

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

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

Question : If the width of the slit in single slit diffraction experiment is doubled, then the central maximum of diffraction pattern becomes
(b) sharper and brighter
(c) sharper and fainter

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

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

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.

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

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

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

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