Q. The mean free path of electrons in a metal is 4 × 10⁻⁸ m. The electric field which can give on an average 2 eV energy to an electron in the metal will be in units of V/m:
A) 5 × 10⁻¹¹
B) 8 × 10⁻¹¹
C) 5 × 10⁷
D) 8 × 10⁷
Explanation
[Solution from source] An electron gains energy eEλ while travelling one mean free path. Setting eEλ = 2 eV gives E = 2 V/(4 × 10⁻⁸ m) = 5 × 10⁷ V/m. The very small values (10⁻¹¹) would come from multiplying by λ instead of dividing. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.