Question

There is a uniform electric field E in the region between two parallel plates. A charged particle with a specific charge s enters the region with a speed u, in a direction parallel to the plates. The length of each plate is l. The deflection of the particle as it crosses the plates is proportional to

(a) E 

(b) s 

(c) l² 

(d) u^-2

Answer 1

Correct Answer is: (a) E, (b) s, (c) l^2, (d) u^-2

As there is no horizontal force, the horizontal component of the velocity remains constant = u.

Time of transit between the plates = t = l/u.

In the vertical direction, F = QE, a = F/m = QE/m.

∴ displacement = 1/2 at² = 1/2 . QE/m (l²/u²) = 1/2 Es (l²/u²).