Question

The work function of sodium is $2.3eV.$ 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
$W_0=2.3eV=2.3\times 1.6\times 10^{-19}J$
where ${\lambda }_0$ is the threshold wavelength for sodium
Then, $W_0=\frac{hc}{{\lambda }_0}$
or ${\lambda }_0=\frac{hc}{W_0}$
${\lambda }_0=\frac{6.6\times 10^{-34}\times 3\times 10^8}{2.3\times 1.6\times 10^{-19}}$
$=5380\times 10^{-10}m$
$=5380\mathring{A}$