Q. 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 :2
B) 4 :1
C) 2 :1
D) 1 :4
Explanation
(c) $W_{0} \propto \frac{1}{\lambda} \Rightarrow \frac{\lambda_{1}}{\lambda_{2}} = \frac{\left( W_{0} \right)_{2}}{\left( W_{0} \right)_{1}} = \frac{4.5}{2.3} = \frac{2}{1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.