Question

If the binding energy of electrons in a metal is $250\, kJ / mol$, what should be the threshold frequency of the striking photons in order to free an electron from the metal surface?

• A. $6.26 \times 10^{14} s^{-1}$
• B. $12.4 \times 10^{14} s^{-1}$
• C. $6.26 \times 10^{12} s^{-1}$
• D. $12.4 \times 10^{12} s ^{-1}$

Answer 1

Answer: (A)

Binding energy of electron $=250 KJ / mol$
Binding energy of one electron
$\left.=\frac{250 \times 10^{3}}{6.023 \times 10^{23}}\right\rfloor$
$ \Rightarrow 4.15 \times 10^{-19} J $
Binding energy $=h v_{0}$
$v_{0}$ is threshold frequency
$ \begin{array}{l} 4.15 \times 10^{-19}=6.625 \times 10^{-34} \times v_{0} \\ v_{0}=6 \times 10^{14} sec ^{-1} \end{array} $