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
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) smaller
(b) 5 times greater
(c) 10 times greater (d) equal
(NEET 2018)​

Answer 1

As you know, electron is charged particle , it experiences elctric force due to present in electric field E . so, the force act on electron , F = eE

F = ma

eE = ma ⇒a = eE/m

, here m is mass of electron.

because electron starts to move in rest , ∴ u = 0 Now, use S = ut + 1/2 at² h = 0 + 1/2 (eE/m)t²

As you know, electron is charged particle , it experiences elctric force due to present in electric field E . so, the force act on electron , F = eE F = maeE = ma ⇒a = eE/m , here m is mass of electron.because electron starts to move in rest , ∴ u = 0 Now, use S = ut + 1/2 at²

h = 0 + 1/2 (eE/m)t²

t = √{2hm/eE}

Similarly in case of proton, t' = √{2hM/pE} , here M is mass of proton

 You also know, magnitude of charge on proton equals electron.

so, e = p

 ∴ t' = √{2hM/eE} 

Here it is clear that ,

 t/t' = √{m/M}

 But mass of proton >> mass of electron 

∴ M >> m ∴ t/t' < 1 t < t'

 Hence, time taken by electron is smaller than time taken by proton.

Answer 2

Answer:

smaller

Explanation:

use the equation,; S= ur+1/2at^2

from this we get t is proportional to √m

therefore, electron is having smaller mass than proton and will take less time