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 $A$, if the stopping potential of $A$ relative to $C$ is :

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

Answer 1

Answer: (A)

$-3V$

Case 1 :

Energy of photon $E=5$ eV

Maximum kinetic energy of photoelectrons $K=2$ 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 $K=6-3=3$ eV

thus stopping potential of A relative to C is $-3$ V.