Question

A photo cell is receiving light from a source placed at a distance of 1 m. If the same source is to be placed at a distance of 2 m, then the ejected electron

• A. Moves with one-fourth energy as that of the initial energy
• B. Moves with one fourth of momentum as that of the initial momentum
• C. Will be half in number
• D. Will be one-fourth in number

Answer 1

The correct option is D Will be one-fourth in number

Number of photons $\propto$ Intensity $\propto ={\frac{1}{\left(distance\right)}}^2$
$\Rightarrow \frac{N_1}{N_2}={\left(\frac{d_2}{d_1}\right)}^2\Rightarrow \frac{N_1}{N_2}-{\left(\frac{2}{1}\right)}^2\Rightarrow N_2=\frac{N_1}{4}$
But the energy of the photo electrons emitted will remain the same