Question

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

• A. 7.5 eV
• B. 2.5 eV
• C. 10 eV
• D. 5 eV

Answer 1

The correct option is B 2.5 eV

${\lambda }_0=5\times {10}^{-7}mw=\frac{hc}{{\lambda }_0}=\frac{12400}{5000}=2.5eV$