Sankalp NEET Full Test-5 Question-18 Solution

Question: 18: After passing through a polariser a linearly polarised light of intensity I is incident on an analyser making an angle of 30^{\circ} with that of the polariser. The intensity of light emitted from the analyser will be :

(1) \frac{I}{2}

(2) \frac{\mathrm{I}}{3}

(3) \frac{3 I}{4}

(4) \frac{21}{3}

Answer: Option (3)

Explanation:

When plane polarised light is incident on an analyser, the intensity of transmitted light is given by Malus’ law.

According to Malus’ law,

I = I_0 \cos^2 \theta

where I_0 is the intensity of incident polarised light on the analyser and \theta is the angle between the transmission axes of the polariser and the analyser.

Here, the light incident on the analyser is already plane polarised with intensity

I_0 = I

The angle between the polariser and analyser is

\theta = 30^{\circ}

Substituting the values,

I = I \cos^2 30^{\circ}

Since,

\cos 30^{\circ} = \frac{\sqrt{3}}{2}

Therefore,

\cos^2 30^{\circ} = \frac{3}{4}

Hence, the intensity of light emerging from the analyser is

I = \frac{3I}{4}

Thus, the correct option is (3).