Force on A Current-carrying Conductor

When a conductor carrying a current is placed in a magnetic field, the conductor experiences a magnetic force.

  • The direction of this force is always right angles to the plane containing both the conductor and the magnetic field, and is predicted by Fleming’s Left-Hand Rule.


left hand rule
Diagram by Jfmelero. Link: Available under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Referring to the diagram above, F is Force, B is Magnetic field, I is current.

Factors affecting magnetic force on a current-carrying conductor in a magnetic field:

  • Strength of the magnetic field
  • Current flowing through the wire
  • Length of the wire


magnetic force
$F = B I l \, sin \, \theta$, where

  • F is force acting on a current carrying conductor,B is magnetic flux density (magnetic field strength),
  • I is magnitude of current flowing through the conductor, 
  • $l$ is length of conductor,
  • $\theta$ is angle that conductor makes with the magnetic field.


When the conductor is perpendicular to the magnetic field, the force will be maximum. When it is parallel to the magnetic field, the force will be zero.


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