A point source S emits unpolarized light uniformly in all directions. At two points A and B , the ratio r = I A / I B of the intensities of light is 2. If a set of two polaroids having 4 5 ∘ angle

Question

A point source S emits unpolarized light uniformly in all directions. At two points A and B , the ratio r = I A ​ / I B ​ of the intensities of light is 2. If a set of two polaroids having 4 5 ∘ angle between their pass-axes is placed just before point B , then the new value of r will be ______

TestHub · Accepted Answer

I ∝ l 2 1 ​ Where I: distance from point source. ​ ⇒ I B ​ I A ​ ​ = I A 2 ​ I B 2 ​ ​ = 2 ⇒ I B ​ = 2 ​ I A ​ . ​ Also, due to polaroids: ​ I B ′ ​ = 2 I B ​ ​ cos 2 4 5 ∘ = 4 I B ​ ​ ⇒ I B ′ ​ = 4 I B ​ ​ … (2) ⇒ Ratio becomes 4 times. ⇒ r new ​ = 8 ​

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