A ray of light of intensity I is incident on a parallel glass slab at… | JEE Main 2013 (9 Apr, Shift 1)

Q27JEE Main 2013 · 9 APR · SHIFT 1Difficult

Biprism, Thin Films & Other Devices

A ray of light of intensity I is incident on a parallel glass slab at point A as shown in the diagram. It undergoes partial reflection and refraction. At each reflection, 25% of incident energy is reflected. The rays AB and A'B' undergo interference. The ratio of $I_{max}$ and $I_{min}$ is:

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Answer: (a)

Ray AB (reflected at A): $I_1 = 0.25I = \frac{16I}{64}$ .
Ray A'B': transmitted $0.75I$ , reflected at C $0.25\times0.75I$ , transmitted at A': $I_2 = 0.75\times0.25\times0.75I = \frac{9I}{64}$ .
$\frac{I_{max}}{I_{min}} = \left(\frac{\sqrt{16}+\sqrt{9}}{\sqrt{16}-\sqrt{9}}\right)^2 = 49$ .
So the answer is (a) 49 : 1.

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