Question

Potassium surface with a work function of $2.30\text{eV}$ is irradiated with a radiation of frequency $9.5\times {10}^{14}\text{Hz}$. Negative potential to be applied to the anode to ensure no electrons reach the anode plate, is,

• A. $3.93\text{eV}$
• B. $2.3\text{eV}$
• C. $8.69\text{eV}$
• D. $1.63\text{eV}$

Answer 1

The correct option is D $1.63\text{eV}$

We know stopping potential $V_s$,
$V_s=\frac{E}{e}-{\varphi }_0$
where $E=hf\to$ Energy of incident radiation in $\text{J}$
${\varphi }_0\to$ work function, in $\text{eV}$

$\therefore V_s=\frac{6.63\times {10}^{-34}\times 9.5\times {10}^{14}}{1.6\times {10}^{-19}}-2.30$
$V_s=3.93-2.3=1.63\text{eV}$

Hence, $\left(D\right)$ is the correct answer.

Why this question? Concept: Stopping potential is the negative potential applied to the anode; to repel electrons from it. Ensuring breaking of circuit.