Question

The maximum wavelength of light that can be used to produce photoelectric effect on a metal is 250 nm. The maximum kinetic energy of the electrons in joule, emitted from the surface of the metal when a beam of light of wavelength 200 nm is used :

• A. $89.61\times {10}^{-22}$
• B. $69.81\times {10}^{-22}$
• C. $18.96\times {10}^{-20}$
• D. $19.86\times {10}^{-20}$

Answer 1

The correct option is D $19.86\times {10}^{-20}$

$K.E{.}_{max}=\frac{hc}{\lambda }-\frac{hc}{{\lambda }_T}$

=$\frac{1240}{200}-\frac{1240}{250}$ (as $hc=1240eV-nm$)

$=6.2-4.96eV$

$=1.24eV$

$=1.24\times 1.6\times {10}^{-19}J$

$=1.986\times {10}^{-19}J$

$=19.86\times {10}^{-20}J$

So, the answer is option (D).