Question

The work function of the target material is $1.24eV$ and the wavelength of incident light is $4360\stackrel{\circ }{A}$. What retarding potential is necessary to stop the emission of the electrons?

• A. $1.61V$
• B. $2.61V$
• C. $3.61V$
• D. $4.61V$

Answer 1

The correct option is A $1.61V$

Maximum kinetic energy of the emitted electrons is given by
$E=\varphi +K.E_{max}$
where $E$ = energy of incident radiation $=\frac{12431}{\lambda \left(\text{in}\stackrel{\circ }{A}\right)}eV=\frac{12431}{4360}eV=2.85eV$
and $\varphi =$ work function of material $=1.24eV$

Therefore, $K.E_{max}=2.85-1.24=1.61eV$



Retarding/Stopping potential is the minimum reverse potential that must be applied to completely stop the movement of electrons.
If $V_0$ is stopping potential, $e{V}_0=1.61eV$
i.e $V_0=1.61V$