Question

In photoelectric effect, the threshold wavelength of sodium is 5000 A. Find its work function. $(h=6.6\times {10}^{-34}Js,c=3\times {10}^8\cdot m{s}^{-1},1eV=1.6\times {10}^{-19}J)$

• A. 7.5 eV
• B. 2.5 eV
• C. 10 eV
• D. 5.0 eV

Answer 1

The correct option is B 2.5 eV

Given, $\lambda =5000A^o=5\times {10}^{-7}m$,

$h=6.6\times {10}^{-34}Js$

$c=3\times {10}^{8}m{s}^{-1}$

The work function of sodium

$W=\frac{hc}{\lambda }$

$W=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{5\times {10}^{-7}}$

or $W=3.96\times {10}^{-19}J$

or $W=2.47eV$ $[\because 1eV=1.6\times {10}^{-19}J]$

or $W=2.5eV$ [Approximately]