Question

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

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

Answer 1

Answer: (B)

-1.2V

Answer 2

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