NEET Physics Question - Wave Optics

Assertion (A): Two polaroids are crossed to each other. When either of them is rotated through \(30^\circ\), then only one eighth of the incident unpolarised light passes through the combination.

Reason (R): According to Malus's law, \(I \propto cos^2 \theta\) where \(I\) is the resultant intensity transmitted and \(theta\) is the angle between the optical axis of analyser and polariser.

Both (A) & (R) are true and the (R) is the correct explanation of the (A)

Both (A) & (R) are true but the (R) is not the correct explanation of the (A)

(A) is true but (R) is false

Both (A) and (R) are false

Solution:

When two crossed polaroids have one rotated by \(30^\circ\), the angle between their axes becomes \(60^\circ\). Incident unpolarised light \(I_0\) reduces to \(I_0/2\) after the first polaroid. By Malus's Law, \(I = (I_0/2) cos^2(60^\circ) = (I_0/2) (1/4) = I_0/8\). Both (A) and (R) are true, and (R) explains (A).

Rankers Physics

Malus’s Law and Polaroids

Solution:

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