Q. Electrons used in an electron microscope are accelerated by a voltage of 25 kV. If the voltage is increased to 100 kV then the de-Broglie wavelength associated with the electrons would
A) Increase by 4 times
B) Increase by 2 times
C) Decrease by 2 times
D) Decrease by 4 times
Explanation
[Solution from source] For electrons accelerated through V, λ = h/√(2meV), so λ ∝ 1/√V. Increasing V from 25 kV to 100 kV (4 times) reduces λ by √4 = 2 times. 'Decrease by 4 times' wrongly takes λ ∝ 1/V. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.