Q 12-11-078JEE MainJEE Main 2023 (29 Jan, Shift 1)Easy
The threshold wavelength for photoelectric emission from a material is $5500\ \text{Å}$. Photoelectrons will be emitted, when this material is illuminated with monochromatic radiation from a
A. $75\ \text{W}$ infra-red lamp
B. $10\ \text{W}$ infra-red lamp
C. $75\ \text{W}$ ultra-violet lamp
D. $10\ \text{W}$ ultra-violet lamp
Choose the correct answer from the options given below:
Answer: (D) C and D only
Emission needs $\lambda<5500\ \text{Å}$, whatever the power of the lamp. Infra-red has $\lambda>7000\ \text{Å}$ and cannot eject electrons; ultra-violet has $\lambda<4000\ \text{Å}$ and can.
So both UV lamps (C and D) work.
Solution by Sreeraj P, M.Sc Physics