A photocell is illuminated by a small bright source placed $1 \mathrm{~m}$ away. When the same source of…

A photocell is illuminated by a small bright source placed $1 \mathrm{~m}$ away. When the same source of light is placed $\frac{1}{2} \mathrm{~m}$ away, the number of electrons emitted by photo cathode would
  1. decrease by a factor of 4
  2. increase by a factor of 4
  3. decrease by a factor of 2
  4. increase by a factor of 2

Solution

$I \propto \frac{1}{r^2}$

Asked in: JEE Main 2005

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