Question

Light of wavelength $\lambda$ falls on a metal having work function hc/ $\lambda_0$ Photoelectric effect will take place only if

• A. $\lambda \,\geq\, \lambda_0$
• B. $\lambda \,\geq\, 2\lambda_0$
• C. $\lambda \,\leq\, \lambda_0$
• D. $\lambda \,< \lambda_0/2$

Answer 1

Answer: (C)

$hv = hv _{0}+ K . E$
$v \,\alpha \frac{1}{\lambda}$
$\Rightarrow \frac{ hc }{\lambda}=\frac{ hc }{\lambda_{0}}+ K . E$
$\therefore K . E =\frac{ hc }{\lambda \lambda_{0}}\left(\lambda_{0}-\lambda\right)$
as $K . E \geq 0 $
$\Rightarrow \lambda_{0}-\lambda \geq 0$
$ \Rightarrow \lambda \leq \lambda_{0}$