Q. An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance h. The time of fall of the electron, in comparison to the time of fall of the proton is
A) 10 times greater
B) 5 times greater
C) smaller
D) equal
Explanation
[Solution] Each particle accelerates at $a = eE/m$ (gravity negligible); $t = \sqrt{2h/a} \propto \sqrt{m}$, so the lighter electron takes less time. Answer (3).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.