Question

The work function of sodium is $2.3 \,eV.$ The threshold wavelength of sodium will be:

• A. $ 2900\,\mathring{A}$
• B. $ 2500\,\mathring{A}$
• C. $ 5380\,\mathring{A}$
• D. $ 1200\,\mathring{A}$

Answer 1

Answer: (C)

Here: work function
$W_{0}=2.3 e V=2.3 \times 1.6 \times 10^{-19} J$
where $\lambda_{0}$ is the threshold wavelength for sodium
Then, $W_{0}=\frac{h c}{\lambda_{0}}$
or $\lambda_{0}=\frac{h c}{W_{0}}$
$\lambda_{0}=\frac{6.6 \times 10^{-34} \times 3 \times 10^{8}}{2.3 \times 1.6 \times 10^{-19}} $
$=5380 \times 10^{-10} m$
$=5380\,\mathring{A}$