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Question:

A plane polarized light is incident on a polariser with its pass axis making angle θ with x-axis, as shown in the figure. At four different values of θ, θ=8o, 38o, 188o and 218o, the observed intensities are same. What is the angle between the direction of polarization and x-axis?

128o

203o

98o

45o

Solution:

Let the angle between polarization direction and x-axis be θ'.
So angle between polarisation direction and pass axis of polariser is (θ'-θ)
Given θ=8o, 88o, 188o, 218o
∴I=Iocos²(θ'-θ)
For θ'=203o intensities are same