Q. An electron in the hydrogen atom jumps from excited state n to the ground state. The wavelength so emitted illuminates a photosensitive material having work function 2.75 eV. If the stopping potential of the photoelectron is 10 V, then the value of n is
A) 5
B) 2
C) 3
D) 4
Explanation
[Solution from source] Photon energy = work function + eV₀ = 2.75 + 10 = 12.75 eV. For hydrogen, 13.6(1 − 1/n²) = 12.75 gives 1/n² = 0.0625, so n = 4. The n = 3 → 1 transition gives only 12.09 eV, too little. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.