JEE Main · 2021 · 24 Feb 2021 · Shift 1 · Wave Optics

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An unpolarized light beam is incident on the polarizer of a polarization experiment and the intensity of light beam emerging from the analyzer is measured as 100 Lumens. Now, if the analyzer is rotated around the horizontal axis (direction of light) by

3 0^{\circ}

in clockwise direction, the intensity of emerging light will be ______ Lumens.

Answer: 75

Solution

When unpolarized light passes through a polarizer, the intensity becomes

I_{0} /2

. After passing through an analyzer at angle

θ

to the polarizer, Malus's law gives:

I = I_{0} cos^{2} θ

Initially, the analyzer is aligned with the polarizer (

θ = 0°

), so:

I_{ini t ia l} = \frac{I _{0}}{2} \times 1 = 100 Lumens

After rotating by

30°

I_{f ina l} = \frac{I _{0}}{2} cos^{2} 30° = 100 \times cos^{2} 30° = 100 \times (\frac{3}{2})^{2} = 100 \times \frac{3}{4} = 75 Lumens

Answer: 75

JEE Main · 2021 · 24 Feb 2021 · Shift 1 · Integer answer

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JEE Main · 2021 · 24 Feb 2021 · Shift 1 · Wave Optics

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