Question

A cesium photo cell, with a steady potential difference of $60$ volt across it, is illuminated by a small bright light placed $50$ cm away. When the same light is placed one meter away, the photoelectrons emerging from the photo cell : (assume that potential difference applied is sufficient to produce saturation current)

• A. each carry one quarter of their previous energy
• B. each carry one quarter of their previous momentum
• C. are half as numerous
• D. are one quarter as numerous

Answer 1

Answer: (D)

number $\int photo$ electronic $\propto \frac{1}{d^2}$

$\frac{N_1}{N_2}={\left(\frac{d_2}{d_1}\right)}^2$

$={\left(\frac{100}{50}\right)}^2$

$=\frac{4}{1}$

$N_2=\frac{N_1}{4}$