Question

Electrons are emitted with zero velocity from a metal surface, when it is exposed to a radiation of wavelength 6800 Å . Then work function of metal is

• A. 2.92 X 10^-19 ergs
• B. 2.92 X 10^-19 J
• C. 2.92 X 10^-19 eV
• D. 2.92 X 10^-19 Cal

Answer 1

The correct option is

D

2.92 X 10^-19 J

Wavelength of radiation is =$6800\times {10}^{-10}m$

Now threshold frequency

$v_o=\frac{c}{\lambda }$

$v_o=\frac{3\times {10}^{8}m{s}^{-1}}{6800\times {10}^{-10}m}=4.41\times {10}^{14}{s}^{-1}$

(work function) =

$w=h{v}_0$

=

${6.626\times 10}^{-34}Js\times 4.41\times {10}^{14}{s}^{-1}$

$Workfunction=2.92\times {10}^{-19}J$

= $\frac{hc}{{\lambda }_0}=\frac{6.625\times {10}^{-34}\times 3\times {10}^8}{6.8{10}^{-10}\times {10}^3}$

= $\frac{3\times 6.625\times {10}^{-19}}{6.8}$

= $2.92\times {10}^{-19}J$