Q. A photosensitive metallic surface has work function, hν₀. If photons of energy 2hν₀ fall on this surface, the electrons come out with a maximum velocity of 4 × 10⁶ m/s. When the photon energy is increased to 5hν₀, then maximum velocity of photoelectrons will be :
A) 16 × 10⁶ m/s
B) 8 × 10⁷ m/s
C) 4 × 10⁵ m/s
D) 8 × 10⁶ m/s
Explanation
[Solution from source] KE_max = E − hν₀. With 2hν₀ it is hν₀; with 5hν₀ it is 4hν₀. Since v ∝ √KE, the speed doubles to 8 × 10⁶ m/s. 16 × 10⁶ m/s wrongly takes v ∝ KE. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.