question_answer 31)

  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:

  (d)There is a uniform magnetic field  inside the current carrying long solenoid acting along the axis of solenoid. The magnitude of force on the electron of charge (- e) moving with velocity  in a magnetic field is Here angle  between and  is zero, i.e., = 0° and sin = 0. Therefore F = 0. It means the electron will continue to move with a uniform velocity along the axis of the solenoid.