Question

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

• A. $1$
• B. $2$
• C. $3$
• D. $4$

Answer 1

Answer: (D)

$4$

$E=\frac{hc}{\lambda }=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}}J$
$E\left(ineV\right)=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{300\times {10}^{-9}\times 1.6\times {10}^{-19}}=4.125eV$
For photoelectric effect to occur, the energy of a photon must be greater than the work function of the metal.

So, the number of metals showing photo-electric effects will be (4) i.e., Li, Na, K, Mg.

Hence, option D is correct.