Question

An electron is projected as shown in fig. with kinetic energy K, at an angle `theta=45^(@)` between two charged plates. Ignore the gravity.

At what distance from the starting point will the electron strike the lower plate?
A. `K//qd`
B. `2K//qd`
C. `K//2qd`
D. infinte

Answer 1

Correct Answer - C
`d=(u^(2)sin^(2)theta)/(2a) [a=(qE)/(m)]`
`=(m u^(2)sin^(2)45^(@))/(2qE)`
`d=(K)/(2qE) or, E=(K)/(2dq)`
`R=(u^2)/(a) = (2d)/(sin^(2)theta)=4d`