Question

What should retarding potential difference be applied between electrodes of the photocell for the photocurrent to drop to zero?

• A. $1.5V$
• B. $2.0V$
• C. $1.8V$
• D. $2.3V$

Answer 1

The correct option is A $1.5V$

The cathode is at a potential $0V$ and the anode potential is $0.6V$.
Wavelength of incident light $\lambda =2.3\times {10}^{-7}m=2300A^o$
Energy of incident light $E=\frac{hc}{\lambda }=\frac{12413}{\lambda \left(in{A}^o\right)}eV$
$\therefore$ $E=\frac{12413}{2300}=5.4eV$
Stopping potential difference required $e{V}_o=E-\varphi$
$\therefore$ $e{V}_o=5.4-4.5=0.9eV$
So potential difference of $0.9V$ must be there in between anode and stopping electrode.
So stopping electrode must have a potential $=0.9+0.6=1.5V$