Question

When a monochromatic point source pf light is at a distance 0.2 m from a photoelectric cell, the saturation current and cut-off voltage are 18.0 mA and 0.6 V. If the same source is placed 0.6 m away from the photoelectric cell, then the saturation current and the stopping potential respectively are

• A. 2mA and 0.2 V
• B. 2mA and 0.6 V
• C. 6mA and 0.2 V
• D. 6mA and 0.6 V

Answer 1

The correct option is B 2mA and 0.6 V

$\begin{array}{c}{K}_{Max}=e{v}_s\\ \text{and}{v}_s\text{is stopping polential ond it is independent}\\ \text{of intensity}so\text{, if light source placed at any where}\end{array}$

$\begin{array}{c}\text{it remains same}\Rightarrow V_s=0.6V\\ \text{while}{I}_s\text{(saturation current) depends on intensity.}\end{array}$

$\begin{array}{cc}& \text{and}I\propto A^2\text{.So if distance increased by}3\text{time}\\ & \text{its intensity decreases by 9 times}\\ & \Rightarrow I_s=2mA\end{array}$