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An unpolarised light beam of intensity 2I₀ is passed through a polaroid P and then through another polaroid Q which is oriented in such a way that its passing axis makes an angle of 30° relative to that of P. The intensity of the emergent light is

Asked in JEE Main 29th July 2nd Shift 2022 · Malus's law and polaroids

• (1) (I₀)/4
• (2) (I₀)/2
• (3) (3I₀)/4
• (4) (3I₀)/2

Step-by-step solution

Why the other options are wrong

• (1) Halves at P correctly but then uses cos² 60°, the complement of the given 30°: I₀×1/4.
• (2) Skips the halving at P and also uses cos² 60°: 2I₀×1/4.
• (4) Forgets to halve the unpolarised 2I₀ at the first polaroid.

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