Force on a current-carrying conductor

When a current carrying conductor is placed in between the magnetic poles, the conductor experience motion. This motion is due to a force is called motor force.

This force is a result of interaction of following two magnetic fields:

  1. the magnetic field due to magnet and
  2. magnetic field around a current carrying conductor.

The direction of motion is perpendicular to the direction of magnetic field (north to south) and direction of conventional current in the conductor.

The strength of motor force is proportional to the following four factors:

  1. Length of the conductor,
  2. strength of magnetic field,
  3. size of the current in the conductor,
  4. angle between the magnetic field lines and the conductor. Motor force is maximum if the angle is 90 degree and minimum force if the angle is zero.

Fleming’s Left hand rule: Fleming’s left hand rule helps us to determine the direction of motor force. According to this rule, extend the thumb, forefinger, and the middle finger of left hand in such a way that all three are mutually perpendicular to each another. If the forefinger points in the direction of the magnetic field from north to south pole and middle figure points in the direction of conventional current from positive to negative, then thumb points in the direction of motor force. Make sure that the direction of current should be from positive to negative terminal of the battery that is the direction of conventional current.


Common example of current carrying conductor in between the magnet is DC motor.