Question

The work functions for metals $A$, $B$ and $C$ are respectively $1.92eV,2.0eV$ and $5eV$. 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
$W=\frac{hc}{\lambda }$
$=\frac{6.62\times 10^{-34}\times 3\times 10^8}{4100\times 10^{-10}}$
$=4.8\times 10^{-19}J$
$=\frac{4.8\times 10^{-19}}{1.6\times 10^{-19}}eV=3eV$
Now, we have
$W_A=1.92eV$,
$W_B=2.0eV$
$W_C=5eV$
Since, $W_A<W$
and $W_B<W$, hence, $A$ and $B$ will emit photoelectrons.