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Physics · Magnetic field due to a magnetic dipole (bar magnet) along its axis and perpendicular to its axis, torque on a magnetic dipole in a uniform magnetic field

A circular ring is fixed in a gravity free space and one point of the ring is ea

A circular ring is fixed in a gravity free space and one point of the ring is earthed. Now a magnet is placed along axis of the ring at a distance from its centre such that the nearer pole is north pole as shown in figure. A sharp impilse is applied on the magnet so that it starts to move towards the ring. Then,

  • A. Initially magnet experiences an acceleration and then it retards to come to an instantaneous rest.
  • B. Magnet starts to oscillate about centre of the ring
  • C. Magnet continues to move along the axis with constant velocity
  • D. The magnet retards and comes to rest finally

Step-by-step solution

As the magnet moves towards the ring, the changing magnetic flux induces a current in the ring. According to Lenz's law, the induced current produces a magnetic field that opposes the motion of the magnet, resulting in a retarding force. This force is always opposite to the velocity, causing the magnet to decelerate continuously. The kinetic energy is dissipated as heat due to the resistance of the ring, so the magnet eventually comes to rest. No restoring force exists, so the motion is aperiodic and damped, without oscillation.
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