Question

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

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

• A. $4$
• B. $3$
• C. $5$
• D. $2$

Answer 1

The correct option is A $4$

The energy associated with incident photon $=\frac{hc}{\lambda }$
$E=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}}J$
$E$ in $ev\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}\times 1.6\times {10}^{-19}}=4.16ev$

Now $Li,Na,K,Mg$ have work function less than 4.14 eV

hence these will show the photoelectric effect

Hence, the correct option is $A$