Question

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

• A. $\lambda \ge {\lambda }_0$
• B. $\lambda \le {\lambda }_0$
• C. $\lambda \le 4{\lambda }_0$
• D. $\lambda =4{\lambda }_0$

Answer 1

Answer: (B)

$\lambda \le {\lambda }_0$

As kinetic energy $K=\frac{hc}{\lambda }-\frac{hc}{{\lambda }_0}$
K is positive, therefore photoelctronic emission will take
place if $\frac{hc}{\lambda }\ge \frac{hc}{{\lambda }_0}$
or$\lambda \le {\lambda }_0$