An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true?

Options

A. The electron will be accelerated along the axis.
B. The electron path will be circular about the axis.
C. The electron will experience a force at `45@` to the axis and hence execute a helical path.
D. The electron will contnue to move with uniform velocity along the axis of the solenoid.

Answer

D

Explanation

Let the electron ( e) is projected with a uniform velocity ( v) in a uniform magnetic field B. The magnetic velocity (v ) in a uniform magnetic field B. The magnitude of force on it is `|vecF|=-e|vecv xx vecB| =-evB sintheta`
As `theta = 0^(@), |vecF| =-evBsin 0^(@)=0`
Hence the electron will continue to move with a uniform velocity along the axis of the solenoid.