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

$\begin {array} {1 1} (a)\;1:2 & \quad (b)\;4:1 \\ (c)\;2:1 & \quad (d)\;1:4 \end {array}$

Ans : (3) 2:1
Work function, $W=hc/\lambda$
So, $W_{Na}/W_{Cu} = \lambda_{Cu}/\lambda_{ Na} = 4.5/2.3 = 2(approx)$