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Question:

Two Polaroids P1 and P2 are placed with their axis perpendicular to each other. Unpolarised light I0 is incident on P1. A third polaroid P3 is kept in between P1 and P2 such that its axis makes an angle 45o with that of P1. The intensity of transmitted light through P2 is:

I0/2

I0/8

I0/16

I0/4

Solution:

The correct option is I0/8
Initial intensity=I0
After P1 → I1 = I0/2
After P3 → I2 = I1cos²45o = I0/2 × 1/2 = I0/4
After P2 → I3 = I2cos²45o = I0/4 × 1/2 = I0/8