CBSE Class 12 Physics 2017 Outside Delhi Set 1 Paper

Question : 6

Total: 26

SECTION -B

Draw the intensity pattern for single slit diffraction and double slit interference. Hence, state two differences between interference and diffraction patterns.
OR
Unpolarised light is passed through a polaroid P1. When this polarised beam passes through another polaroid P2 and if the pass axis of P2 makes angle θ with the pass axis of P1, then write the expression for the polarised beam passing through P2. Draw a plot showing the variation of intensity when θ varies from 0 to 2π.

Solution:

Interference pattern
Diffraction pattern
Two Differences

Differences:

Interference	Diffraction
All maxima have equal intensity.	Maxima have different (rapidly decreasing) intensity.
All fringes have equal width.	Different (changing) width.
Superposition of two wavefronts.	Superposition of wavelets from the same wavefront.

OR
Expression for intensity of polarized beam
Plot of intensity variation with angle
Intensity is ‌

cos2θ (if I0 is the intensity of unpolarised light.)
Intensity is Icos2θ (if I is the intensity of polarized light.)
(Award 1∕2 mark if the student writes the expression as I0cos2θ )

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