Q. The work functions for sodium and copper are $2eV$ and $4eV.$ Which of them is suitable for a photocell with $4000\ \mathring{\mathrm{A}}$ light
A) Copper
B) Sodium
C) Both
D) Neither of them
Explanation
(b) Threshold wavelength for $Na,\ \lambda_{Na} = \frac{12375}{2} = 6187.5\mathring{\mathrm{A}}$
Also$\ \lambda_{Cu} = \frac{12375}{4} = 3093.75$
Since$\ \lambda_{Na} > 4000\mathring{\mathrm{A}};$ So$\ Na\ $is suitable
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.