Question

An electron enters the region between the plates of a parallel-plate capacitor at an angle θ to the plates. The plate width is l and the plate separation is d. The electron follows the path shown, just missing the upper plate. Neglect gravity.

(a) tan θ = 2d/l

(b) tan θ = 4d/l

(c) tan θ = 8d/l

(d) The data given is insufficient to find a relation between d, l, θ. 

Answer 1

Correct Answer is: (b) tan θ = 4d/l

The motion is identical to that of a projectile, with the constant electrical force acting as the gravitational force. Treat l as the horizontal range and, d as the maximum height.