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GUJCET · Physics · Moving Charges and Magnetism

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

  1. A The electron path will be circular about the axis.
  2. B The electron will be accelerated along the axis.
  3. C The electron will experience a force at \(45^{\circ}\) to the axis and hence execute a helical path.
  4. D The electron will continue to move with uniform velocity along the axis of the solenoid.
Verified Solution

Answer & Solution

Correct Answer

(D) The electron will continue to move with uniform velocity along the axis of the solenoid.

Step-by-step Solution

Detailed explanation

D
The electron is moving in along the direction of axis and the magnetic field is always along the axis. Thus, the velocity of electron and magnetic field is parallel to each other. Therefore the angle between them is \(\theta=0^{\circ}\)
So, \(F =q uB \sin \theta\)
\(\begin{array}{l} F =e v B \sin \theta \\ F =0\left(\because \sin 0^{\circ}=0\right)\end{array}\)
Since the force acting on the electron is 0 , according to Newton's first law of motion, the electron will continue to move in the same direction with uniform velocity.