Question

The work function $\left(\Phi \right)$ of some metals are listed below. The number of metals which will show photoelectric effect, when a light of 300 nm wavelength falls on the metal, are:

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

Answer 1

Energy of photon,

$E=\frac{hc}{\lambda }J=\frac{hc}{e\lambda }eV=\frac{6.625\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}\times 1.602\times {10}^{-19}}=4.14eV$

For the photoelectric effect, $\varphi <E=4.14$

Here, only $Li,Na,K,$ and $Mg$ have work functions less than 4.14 V.

So, only these metals will show the photoelectric effect with this photon.