Question

An electron with kinetic energy E collides with a hydrogen atom in the ground state. The collision will be elastic 

(A)  For all values of E 

(B)  For E < 10.2 eV 

(C)  For 10.2 eV < E < 13.6 eV only 

(D)  For 0 < E < 3.4 eV only

Answer 1

Correct option (B) For E < 10.2 eV

Explanation:

When e^– collide with atom which is massive in comparison to e– . Max possible loss of KE = KE of e^– (initial KE) = E if this E is less than min excitation energy then collision is elastic

∴  E < 10.2 eV (Minimum excitation energy)