Question

The work functions for metals $A$, $B$ and $C$ are respectively $1.92\, eV, 2.0 \,eV$ and $5 \,eV$. According to Einsteins equation, the metals which will emit photoelectrons for a radiation of wavelength $ 4100\,\mathring{A}$ is/are

• A. none
• B. A only
• C. A and B only
• D. all the three metals

Answer 1

Answer: (C)

That metal will emit photoelectrons which has work function lower than that obtained with the radiation of $ 4100\,\mathring{A}$
Work function for wavelength of $4100\, \mathring{A}$ is
$W=\frac{h c}{\lambda} $
$=\frac{6.62 \times 10^{-34} \times 3 \times 10^{8}}{4100 \times 10^{-10}}$
$=4.8 \times 10^{-19}\, J $
$=\frac{4.8 \times 10^{-19}}{1.6 \times 10^{-19}} e V=3\, e V$
Now, we have
$W_{A}=1.92 \,eV$,
$W_{B}=2.0\, eV $
$W_{C}=5 \,eV$
Since, $W_{A} < W$
and $W_{B} < W$, hence, $A$ and $B$ will emit photoelectrons.