An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E . The direction of electric filed is now reversed, keeping its magnitude the same

Question

An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E . The direction of electric filed 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 isNEET 2018

TestHub · Accepted Answer

Acceleration of charge q of mass m in uniform electric field is given as a = q E m . Applying second equation of motion, S = u t + 1 2 a t 2 . Initially mass is at rest, so u = 0 . h = 0 + 1 2 q E m t 2 ⇒ t = 2 h m q E ⇒ t ∝ m as mass of proton is heavier than electron, hence electron will take less time.

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