A uniform electric field exists in a region between two oppo

A uniform electric field exists in a region between two oppositely charged plates. An electron is released from rest at the surface of the negatively charged plate and strikes the surface of the opposite plate, 3.0 cm away, in a time 9.0 x 10^-8 s. (a) What is the speed of the electron as it strikes the second plate (b) What is the magnitude of the electric field?

Solution

From Second equation of kinematics: S=ut+(1/2)at²

As electron is released from rest, so u=0

a=2S/t²

S = 3x10-2 meter, t=9.0x10^-8 second

(a) Velocity V=u+at =at=(2S/t²)*t =2S/t = 2x3x10^-2/9.0x10^-8 =0.67x10⁶ m/s

(b) Force on electron in electric filed = qE

From newton equation ma=qE

E=ma/q

m=mass of electron = 9.11x10^-31kg, q=charge on electron=1.6x10^-19 C

E= 2mS/qt² = 2x9.11x10^-31x3x10^-2/1.6x10^-19x(9.0x10^-8)² = 42.18 N/C