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Chapter 9: Wave Optics
Class XII – Physics Maximum Marks: 21 Time Allowed: 1 Hour 30 Minutes
General Instructions:
This question paper consists of 2 Sections A and B.
All questions are compulsory.
Use of calculator is not permitted.
Draw neat and labeled diagrams wherever required.
Section A (2 Marks Each)
How does the fringe width, in Young’s double-slit experiment, change when the distance of separation between the slits and screen is doubled?
How does the angular separation between fringes in single-slit diffraction experiment change when the distance of separation between the slit and screen is doubled?
In Young’s double slit experiment, using monochromatic light of wavelength , the intensity of light at a point on the screen where path difference is , is K units. Find out the intensity of light at a point where path difference is .
Section B (5 Marks Each)
(a) In Young’s double slit experiment, deduce the conditions for obtaining constructive and destructive interference fringes. Hence deduce the expression for the fringe width. (b) Show that the fringe pattern on the screen is actually a superposition of single slit diffraction from each slit. (c) What should be the width of each slit to obtain 10 maxima of the double slit pattern within the central maximum of the single slit pattern, for green light of wavelength 500 nm, if the separation between two slits is 1 mm?
(a) Write the expression for the resultant intensity at a point due to the superposition of two monochromatic waves and Where is the phase difference between the two waves and a and denote the amplitude and angular frequency. (b) In Young’s double slit experiment using monochromatic light of wavelength l, the intensity of light at a point on the screen where path difference is l is k units. Find the intensity at a point on the screen where path difference is .
(a) Consider two coherent sources S1 and S2 producing monochromatic waves to produce interference pattern. Let the displacement of the wave produced by S1 be given by and by S2 be )Find out the expression for the amplitude of the resultant displacement at a point and show that the intensity at that point will be . Hence establish the conditions for constructive and destructive interference. (b) What is the effect on the interference fringes in Young’s double slit experiment when (i) the width of the source slit is increased; (ii) the monochromatic source is replaced by a source of white light?
