Question

Objective: To perform some calculations involving magnetic forces on charged particles, and involving magnetic flux created by a magnetic field.

1. An electron is moving in the +x direction at a constant speed in a region of space.

a. If there is no external magnetic field (that is, no magnetic field beyond that created by the electron), what is the strength of the external electric field in this region of space? Justify your answer in terms of forces.

b. If there is no external electric field (that is, no electric field beyond that created by the electron), must the external magnetic field strength equal zero in this region of space? Justify your answer.

Answer 1

Answer:-

As we given that electron is moving with constant speed so, for constant speed there must acceleration zero. Hence the electric field mainly produces the acceleration so for constant speed electric field must be zero.

Answer(b)

As electric field is zero then acceleration is also zero, then if magnetic field is perpendicular to the speed then the magnetic force will also be perpendicular to the speed and magnetic field F=q(V×B).

So due to this force work done will be zero hence it will move by constant speed but direction will be changed .

Here we can better say speed will be constant but velocity will change.

So , for constant speed we must have zero magnetic field.