A point source S emits unpolarized light uniformly in all directions. At two points A and B, the ratio $\mathrm{r}=\mathrm{I}_{\mathrm{A}} / \mathrm{I}_{\mathrm{B}}$ of the intensities of light is 2. If a set of two polaroids having 45° angle between their pass-axes is placed just before point B , then the new value of $r$ will be ____.

JEE Advanced · 2024 · 26 May 2024 · Paper 1 · Wave Optics

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 45° angle between their pass-axes is placed just before point B , then the new value of

r

will be ____.

Answer: 8

Solution

When unpolarized light passes through the first polaroid, its intensity becomes

I_{B} /2

. After passing through the second polaroid at 45°, the intensity becomes

I_{B}^{'} = (I_{B} /2) cos^{2} 4 5^{\circ} = I_{B} /4

. The new ratio is

r^{'} = \frac{I _{A}}{I _{B} /4} = \frac{4 I _{A}}{I _{B}} = 4 \times 2 = 8

JEE Advanced · 2024 · 26 May 2024 · Paper 1 · Integer answer

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