Question

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

Answer:

Let the electron (e) is projected with a uniform velocity (v) in a uniform magnetic field B. The magnitude of force on it is ∣

F

ˉ

∣=−e∣

v

ˉ

×

B

ˉ

∣=−evBsinθ

As θ=0

0

,∣

F

ˉ

∣=−evBsin0

0

Hence the electron will continue to move with uniform velocity along the axis of the solenoid.