Question

The maximum wavelength of a beam of light that can be used to produce photoelectric effect on a metal is 250 nm. The 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

Answer: (D)

Here $\lambda_0=250 nm =250 \times 10^{-9} m$
$\lambda=200 nm =200 \times 10^{-9} m$
According to Einstein's photoelectric equation,
$K=h v-h v_0,=\frac{h c}{\lambda}-\frac{h c}{\lambda_0}=h c\left[\frac{1}{\lambda}-\frac{1}{\lambda_0}\right]$
$=6.63 \times 10^{-34} \times 3 \times 10^8 \times\left[\frac{1}{200}-\frac{1}{250}\right] \times \frac{1}{10^{-9}}$
$\therefore K=19.89 \times 10^{-20} J$