CBSE Class 12 Physics Wave Optics MCQs Set B

Question. Which one of the following phenomena is not explained by Huygen’s construction of wavefront ?
(a) Refraction
(b) Reflection
(c) Diffraction
(d) Origin of spectra

Answer : D

Question. The frequency of a light wave in a material is 2 × 10¹⁴ Hz and wavelength is 5000 Å. The refractive index of material will be
(a) 1.50
(b) 3.00
(c) 1.33
(d) 1.40

Answer : B

Question. The refractive index of water is 1.33. What will be the speed of light in water?
(a) 4 × 10⁸ m/s
(b) 1.33 × 10⁸ m/s
(c) 3 × 10⁸ m/s
(d) 2.25 × 10⁸ m/s

Answer : D

Question. Light travels through a glass plate of thickness t and having a refractive index m. If c is the velocity of light in vacuum, the time taken by light to travel this thickness of glass is
(a) t/μc
(b) μt/c
(c) tmc
(d) tc/μ

Answer : B

Question. In Young’s experiment, two coherent sources are placed 0.90 mm apart and fringes are observed one metre away. If it produces second dark fringe at a distance of 1 mm from central fringe, the wavelength of monochromatic light is used would be
(a) 60 × 10^–4 cm
(b) 10 × 10^–4 cm
(c) 10 × 10^–5 cm
(d) 6 × 10^–5 cm

Answer : D

Question. In Young’s double slit experiment, the fringes width is found to be 0.4 mm. If the whole apparatus is immersed in water of refractive index 4/3 , without disturbing the geometrical arrangement, the new fringe width will be
(a) 0.30 mm
(b) 0.40 mm
(c) 0.53 mm
(d) 450 micron.

Answer : A

Question. Assume that light of wavelength 600 nm is coming from a star. The limit of resolution of telescope whose objective has a diameter of 2 m is
(a) 3.66 × 10^–7 rad
(b) 1.83 × 10^–7 rad
(c) 7.32 × 10^–7 rad
(d) 6.00 × 10^–7 rad

Answer : A

Question. An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of
(a) small focal length and large diameter
(b) large focal length and small diameter
(c) large focal length and large diameter
(d) small focal length and small diameter.

Answer : C

Question. A beam of light of l = 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between first dark fringes on either side of the central bright fringe is
(a) 1.2 cm
(b) 1.2 mm
(c) 2.4 cm
(d) 2.4 mm

Answer : D

Question. A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct?
(a) The angular width of the central maximum will decrease.
(b) The angular width of the central maximum will be unaffected.
(c) Diffraction pattern is not observed on the screen in the case of electrons.
(d) The angular width of the central maximum of the diffraction pattern will increase.

Answer : A

Question. A parallel beam of light of wavelength l is incident normally on a narrow slit. A diffraction pattern formed on a screen placed perpendicular to the direction of the incident beam. At the second minimum of the diffraction pattern, the phase difference between the rays coming from the two edges of slit is
(a) 2Π
(b) 3Π
(c) 4Π
(d) Πl

Answer : C

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

Answer : C

Question. In Young’s double slit experiment, if the slit widths are in the ratio 1 : 2, the ratio of the intensities at minima and maxima will be
(a) 1 : 2
(b) 1 : 3
(c) 1 : 4
(d) 1 : 9

Answer : D

Question. The phenomenon of interference is shown by
(a) longitudinal mechanical waves only
(b) transverse mechanical waves only
(c) non-mechanical transverse waves only
(d) All of the above

Answer : D

Question. Angular width (B) of central maxima of a diffraction pattern of a single slit does not depend upon
(a) distance between slit and source
(b) wavelength of the light used
(c) width of slit
(d) frequency of light used

Answer : A

Question. The transverse nature of light is shown by
(a) interference of light
(b) refraction of light
(c) polarization of light
(d) dispersion of light

Answer : C

Question. Two slits in Young’s experiment have widths in the ratio 1 : 25. The ratio of intensity at the maxima and minima in the interference pattern, Imax /I min is
(a) 49/121
(b) 4/9
(c) 9/4
(d) 121/49

Answer : C

Question. In the Young’s double slit experiment, the intensity of light at a point on the screen where the path difference l is K, (l being the wavelength of light used). The intensity at a point where the path difference is l/4 will be
(a) K
(b) K/4
(c) K/2
(d) zero

Answer : CQuestion. Interference was observed in interference chamber where air was present, now the chamber is evacuated, and if the same light is used, a careful observer will see
(a) no interference
(b) interference with brighter bands
(c) interference with dark bands
(d) interference with larger width.

Answer : D

Question. If yellow light emitted by sodium lamp in Young’s double slit experiment is replaced by monochromatic blue light of the same intensity
(a) fringe width will decrease
(b) fringe width will increase
(c) fringe width will remain unchanged
(d) fringes will becomes less intense

Answer : A

Question. Ratio of intensities of two waves are given by 4 : 1. Then ratio of the amplitudes of the two waves is
(a) 2 : 1
(b) 1 : 2
(c) 4 : 1
(d) 1 : 4

Answer : A

Question. Interference is possible in
(a) light waves only
(b) sound waves only
(c) both light and sound waves
(d) neither light nor sound waves

Answer : C

Question. Young’s double slit experiment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5th dark fringe lies in air. The refractive index of the medium is nearly
(a) 1.59
(b) 1.69
(c) 1.78
(d) 1.25

Answer : C

Question. The intensity at the maximum in a Young’s double slit experiment is I0. Distance between two slits is d = 5l, where l is the wavelength of light used in the experiment. What will be the intensity in front of one of the slits on the screen placed at a distance D = 10d ?
(a) 3/4 I₀
(b) I₀/2
(c) I₀
(d) I_0^/ 4

Answer : B

Question. In Young’s double slit experiment carried out with light of wavelength (l) = 5000 Å, the distance between the slits is 0.2 mm and the screen is at 200 cm from the slits. The central maximum is at x = 0. The third maximum (taking the central maximum as zeroth maximum) will be at x equal to
(a) 1.67 cm
(b) 1.5 cm
(c) 0.5 cm
(d) 5.0 cm

Answer : B

Question. If a wave can be polarized, it must be
(a) a transverse wave
(b) a longitudinal wave
(c) a sound wave
(d) a stationary wave

Answer : A