Question

Photons with energy $5eV$ are incident on a cathode $C$ in a photoelectric cell. The maximum energy of emitted photo electrons is $2eV$. When photons of energy $6eV$ are incident on $C$, no photoelectrons will reach the anode $A$. The stopping potential of $A$ relative to $C$ is

• A. $-3V$
• B. $+3V$
• C. $+4V$
• D. $-1V$

Answer 1

The correct option is A $-3V$

Case 1 :
Energy of photon $\left(h\nu \right)$, $E=5$ $eV$
Maximum kinetic energy of photoelectrons $\left(eV\right)$, $K=2$ eV
Using $K=E-\varphi$, where $\varphi$ is the work function
$\therefore$ $2=5-\varphi$ $⟹\varphi =3$ $eV$

Case 2 :
$E=6$ $eV$
$\therefore$ Maximum kinetic energy of photoelectrons, $K=e{V}_0=6-3=3$ $eV$
$V_0=3V$
Thus stopping potential of A relative to C is $-3$ $V$