Question

An electron is traveling at 2.3 *10^3m/s, enters perpendicular to the electric field between two horizontal charged parallel plates. If the electric field strength is 1.5*10^2V/m calculate the time taken for the electron to deflect a distance of 1.0*10^-2 toward the positive plate. Ans: 2.8*10^-8s

Answer 1

speed << speed of light so forget special relativity
F = q E = 1.6*10^-19 * 1.5*10^2
a = F/m = 1.6 * 10^-19 * 1.5*10^2 / (9.1 * 10^-31)
= (1.6*1.5 / 9.1) * 10^14 m/s^2 = 0.264 * 10^14
d = (1/2) a t^2
10*-2 = 0.132 * 10^14 t^2
t^2 = (1/0.132) * 10^-16
t = sqrt(7.58) * 10^-8 = 2.75 *10^-8 seconds,

not long but it goes (2.3*10^3) (2.75*10^-8) = 6.3 * 10^-5 meters forward during that time