Question

Sodium and copper have work functions 2.3 eV and 4.5 eV respectively. Then, the ratio of their threshold wavelengths is nearest to

• A. 1:02
• B. 2:01
• C. 1:04
• D. 4:01

Answer 1

Answer: (B)

2:01

Answer 2

Work function(W) $=\frac{\text { hc }}{\lambda}$ where, $h =$ Planck's constant, $c=$ velocity of light Therefore, $\frac{w_{ na }}{w_{ cu }}=\frac{\lambda_{ cu }}{\lambda_{ na }}$ $\frac{\lambda_{ Na }}{\lambda_{ cu }}=\frac{ W _{ cu }}{ w _{ na }}=\frac{4.5}{2.3}=2$ (nearly)