Question

The work function $(\phi)$ of some metals is listed below. The number of metals which will show photoelectric effect when
light of $300\, nm$ wavelength falls on the metal is

Metal	Li	Na	K	Mg	Cu	Ag	Fe	pt	W
$\phi$ (eV)	2.4	2.3	2.2	3.7	4.8	4.3	4.7	6.3	4.75

Answer 1

Energy of photon
$\frac{h c}{\lambda} J=\frac{h c}{e \lambda} e V=\frac{6.625 \times 10^{-34} \times 3 \times 10^{8}}{300 \times 10^{-9} \times 1.602 \times 10^{-19}}$
For photoelectric effect to occur, energy of incia must be greater than work function of metal.
Hence $Na , K$ and $Mg$ have work functions less than $4.14$