1) 1. Which of the following statements is NOT true about two coherent wave sources? a) They have same frequency / 𝘔𝘦𝘳𝘦𝘬𝘢 𝘮𝘦𝘮𝘱𝘶𝘯𝘺𝘢𝘪 𝘧𝘳𝘦𝘬𝘶𝘦𝘯𝘴𝘪 𝘺𝘢𝘯𝘨 𝘴𝘢𝘮𝘢 b) They have constant phase difference / 𝘔𝘦𝘳𝘦𝘬𝘢 𝘮𝘦𝘮𝘱𝘶𝘯𝘺𝘢𝘪 𝘱𝘦𝘳𝘣𝘦𝘻𝘢𝘢𝘯 𝘧𝘢𝘴𝘢 𝘺𝘢𝘯𝘨 𝘵𝘦𝘵𝘢𝘱 c) They have same wavelength / 𝘔𝘦𝘳𝘦𝘬𝘢 𝘮𝘦𝘮𝘱𝘶𝘯𝘺𝘢𝘪 𝘱𝘢𝘯𝘫𝘢𝘯𝘨 𝘨𝘦𝘭𝘰𝘮𝘣𝘢𝘯𝘨 𝘺𝘢𝘯𝘨 𝘴𝘢𝘮𝘢 d) They can have different colours / 𝘔𝘦𝘳𝘦𝘬𝘢 𝘣𝘰𝘭𝘦𝘩 𝘮𝘦𝘮𝘱𝘶𝘯𝘺𝘢𝘪 𝘸𝘢𝘳𝘯𝘢 𝘺𝘢𝘯𝘨 𝘣𝘦𝘳𝘣𝘦𝘻𝘢 2) When two waves combine to form a new wave with a larger amplitude, it is called  a) constructive b) destructive c) resonant d) diffraction 3) Which of the following will increase the spacing of Young's double slit fringes a) A blue light (450nm) is used instead of a red light (650 nm) b) the screen is moved closer to the slits c) the slits are moved closer together d) Each slit is made wider 4) Which light source is incoherent? a) Light sources from diffraction grating b) Light of the same frequencies from two separate sources c) Light that is partially reflected from the front and back layers of thin film d) Light sources from a narrow double-slits after passing through a single-slit 5) Two coherent sources emit waves of wavelength λ in phase. Constructive interference occurs at a point if the path difference is a) mλ/2 b) mλ c) (m+0.5)λ d) (m-0.5)λ 6) In Young's two-slit experiment, a source of green light is used. The separation of fringes in the interference pattern produced can be increased by increasing a) the distance between the screen and the slit b) the size of every slit c) the distance between the two slits d) the intensity of the green light 7) What happens to the double-slits interference pattern when the two slits are made further apart while the slit size of each slit remains the same? a) Number of fringes remains the same and the fringe width increases. b) Number of fringes increase and the fringe width decreases. c) Number of fringes remains the same and the fringe width decreases d) Number of fringes decreases and the fringe width decreases. 8) The figure below shows two coherent sources P and Q oscillating in phase. If the two waves meet and produce a bright fringe at the point R, the path difference between the two waves at R is a) 0λ b) 0.25λ c) 0.50λ d) 0.75λ 9) In a Young's double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing onthe screen, the screen-to-slit distance D must be changed to:  a) D/2 b) D/4 c) D d) 2D 10) What is meant by monochromatic light? a) A light source with one wavelength only b) A light source with one speed only c) A light source with only white light d) A light source with no wave 11) White light is incident on a soap film of refractive index 1.30 in air. The reflected light looks bluish because the red light of wavelength 670 nm is absent in the reflection. State the condition for destructive interference. a) 2nt=(m+1/2)λ b) 2nt=mλ c) 2t=mλ d) 2t=(m+1/2)λ 12) Light is incident on reflective coating will experience a phase change of a) π rad b) 2π rad c) π/2 rad d) 0 rad 13) A lens (n=1.52) is coated with a film of magnesium fluoride (n=1.25). What should be the least thickness of the film in order to minimize reflected light with a wavelength of 550 nm? a) 6.0 x 10^-7 m b) 1.8 x 10^-6m c) 1.1 x 10^-7m d) 4.8 x 10^-6m 14) The bending of the light as they travel around obstacles is a) refraction b) reflection c) interference d) diffraction 15) What happen to the wavelength and frequency of light when it travels from air to film? a) The wavelength decrease and frequency decrease b) The wavelength increase and frequency increase c) The wavelength decrease and frequency unchanged d) The wavelength unchanged and frequency decrease 16) Light of wave length 350nm is incident on a slit of width 0.5mm . Which of the following expressions corresponds to the angle at which the second order minimum is formed a) sinθ= 2.4 x 10 -3 b) sinθ= 1.4 x 10 -3 c) sinθ= 1.4 x 10 -2 d) sinθ= 2.4 x 10 -2 17) Light of wavelength 250nm is incident on a slit of width 0.3 mm and 1m away from the screen. Find the width of central bright a) 1.67x 10 -4 b) 1.67x 10 -3 c) 1.67x 10 -2 d) 1.67x 10 -1 18) Light of wavelength 250nm is incident on a slit of width 300nm. Find maximum dark fringes can observed in the screen a) 3 b) 2 c) 5 d) 6 19) Light of wavelength 650nm is incident on a diffraction grating of slit width 2x10⁻⁶m. Find how may maximum fringes can observed on the screen a) 3 b) 2 c) 7 d) 6 20) Diffraction grating has 6 × 10⁵ lines per mm. Find the slit separation of the grating a) 1.67x 10 -4 b) 1.67x 10 -9 c) 1.67x 10 -6 d) 1.67x 10 -5

Chapter 8.0 PHYSICAL OPTICS

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