Ncert Exercises & Solutions

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

1.	The electron will be accelerated along the axis.
2.	The electron path will be circular about the axis.
3.	The electron will experience a force at 45° to the axis and hence execute a helical path.
4.	The electron will continue to move with uniform velocity along the axis of the solenoid.

(d) Hint: The magnetic force on a charged particle depends on its initial direction.

The electron is projected with uniform velocity along the axis of a current-carrying long solenoid,

Magnetic Lorentz force,

F = - evBsin 180 ° = 0

as magnetic field and velocity are parallel. The electron will continue to move with uniform velocity along the axis of the solenoid.