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

Answer

D

Explanation

For a current carrying long solenoid, the magnetic field in uniform inside the solenoid and is directed along its axis. It is given by:
` B = mu_(0) n I`
where n-number of twins per unit length of the solenoid
I = current flowing through solenoid
The magnitude of force acting on a moving charge 4 in an external magnetic field is given by:
`F = q vec v xx vec B = q vB sin theta`
Where v = velocity of charge
`theta = ` angle between v and B
Here, ` q = - e`
And ` theta = 0^(@)`
` :. " " F = - e vB sin 0^(@) = 0 `
So, no magnetic force will act on the electron due to magnetic field of the solenoid and it will continue to move along the axis of solenoid with a uniform velocity.
Hence, option (d) is correct.