Question

The work function of 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
$\varphi$ eV	2.4	2.3	2.2	3.7	4.8	4.3	4.7	6.3	4.75

• A.
  4
• B.
  6
• C.
  5
• D.
  9

Answer 1

The correct option is A

4
Given information :
Wavelength of the incident radation = 300 nm = $3000\stackrel{o}{A}$
We know,
$E\left(ev\right)=\frac{12400}{\lambda \left(\stackrel{o}{A}\right)}$
$=\frac{12400}{3000}=4.13eV$


Those metals with work functions below 4.13 eV will show photoelectric effect. So the metals Li, Na, K, and Mg will show photoelectric effect.