Question

Light of wavelength $\lambda$ falls on a metal having work function $\frac{hc}{{\lambda }_0}$. Photoelectric effect will take place only if

• A. $\lambda \ge {\lambda }_0$
• B. $\lambda \ge 2{\lambda }_0$
• C. $\lambda \le {\lambda }_0$
• D. $\lambda <\frac{{\lambda }_0}{2}$

Answer 1

The correct option is C

$\lambda \le {\lambda }_0$

So photo electric effect will only be shown if the energy of each photon is more than the work function.

Wavelength of light used is $\lambda$

So energy of each photon is$\frac{hc}{\lambda }$
Now this should be greater than work function

$\frac{hc}{\lambda }\ge \frac{hc}{{\lambda }_0}$

$\Rightarrow \lambda \le {\lambda }_0$