Question

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

• 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 continue to move with uniform velocity along the axis of the solenoid.

Answer 1

The correct option is D The electron will continue to move with uniform velocity along the axis of the solenoid.

Let the electron (e) is projected with a uniform velocity (v) in a uniform magnetic field B. The magnitude of force on it is $|\overline{F}|=-e|\overline{v}\times \overline{B}|=-evB\sin \theta$

As $\theta =0^0,|\overline{F}|=-evB\sin 0^0$
Hence the electron will continue to move with uniform velocity along the axis of the solenoid.