Question

Sodium and copper have work functions $2.3eV$ and $4.5eV$ respectively. Then the ratio of the wavelengths is nearest to :

• A. 1: 2
• B. 4: 1
• C. 2: 1
• D. 1: 4

Answer 1

Answer: (C)

Work function $W=\frac{hc}{\lambda }$
[Here they are interested in asking threshold wavelength ]
where, $h=$ Planck's constant, $c=$ velocity of light.
Therefore, $\frac{W_{Nd}}{W_{Cu}}=\frac{{\lambda }_{C.u}}{{\lambda }_{Va}}$
$\frac{{\lambda }_{Na}}{{\lambda }_{Cu}}$
$=\frac{W_{Cu}}{W_{Na}}=\frac{4.5}{2.3}=2$ (nearly)