Question

The potential difference that must be applied to stop the fastest photo electrons emitted by a nickel surface, having work function $5.01eV$, when ultraviolet light of $200nm$ falls on it, must be

• A. 2.4V
• B. -1.2V
• C. -2.4V
• D. 1.2V

Answer 1

Answer: (B)

Here,
Incident wavelength, $\lambda =200nm$
Work function, ${\varphi }_0=5.01eV$
According to Einstein's photoelectric equation
$e{V}_s=hv-{\varphi }_0$
$e{V}_s=\frac{hc}{\lambda }-{\varphi }_0$
where $V_s$ is the stopping potential
$eVs=\frac{(1240eVnm)}{(200nm)}-5.01eV$
$=6.2eV-5.01eV=1.2eV$
Stopping potential, $V_s=1.2V$
The potential difference that must be applied to
stop photoelectrons $=-V_s=-1.2V$