The electrons move with a velocity of 3.8 ×107 m/s. What electric field strength is needed to accelerate electrons from rest to this velocity in a distance of 5.0 mm?

Missing part of question

The electron beam inside an old television picture tube is 0.40 mm in diameter and carries a current of 50 μA. This electron beam impinges on the inside of the picture tube screen. 1-The electrons move with a velocity of 3.8 ×107 m/s. What electric field strength is needed to accelerate electrons from rest to this velocity in a distance of 5.0 mm?

Explanation:

From kinematics we know that  

where v and u are final and initial velocities respectively, s is the distance covered, a is acceleration.

We know that initial velocity is zero hence

and making a the subject then

From Newton’s law, F=ma and also qE=ma hence