Question

The work function $\left(\varphi \right)$ of some metal is listed below. The number of metal which will show photoelectric effect when light of $300nm$ wavelength falls on metal is:

Metal	$Li$	$Na$	$K$	$Mg$	$Cu$	$Ag$	$Fe$	$Pt$	$W$
$\varphi \left(eV\right)$	$2.4$	$2.3$	$2.2$	$3.7$	$4.8$	$4.3$	$4.7$	$6.3$	$4.75$

Answer 1

Ejection of electron takes place only when the absorbed energy is greater than work function.
$E_{absorbed}=\frac{hc}{\lambda }=\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}}$
$=6.626\times {10}^{-19}J=\frac{6.626\times {10}^{-19}}{1.6\times {10}^{-19}}eV=4.14eV$
Thus, electron will be ejected from four metals, i.e., $Li$, $Na$, $K$, $Mg$.