zaro

What is Fleming's Law?

Published in Electromagnetism 2 mins read

Fleming's Law describes the relationship between the direction of motion, magnetic field, and current in an electric motor or generator. It's actually comprised of two rules: the left-hand rule and the right-hand rule.

Fleming's Left-Hand Rule

This rule determines the direction of the force acting on a current-carrying conductor placed within a magnetic field. Imagine holding your left hand with your:

  • Thumb: Pointing in the direction of motion of the conductor.
  • Index finger: Pointing in the direction of the magnetic field (from North to South).
  • Middle finger: Pointing in the direction of the current (conventional current flow).

If you align your hand this way, the three fingers will be mutually perpendicular, illustrating the directions of motion, field, and current. The force on the conductor is given by the formula F = BIL, where F is the force, B is the magnetic flux density, I is the current, and L is the length of the conductor within the field.

Fleming's Right-Hand Rule

This rule is used to determine the direction of the induced electromotive force (EMF) or voltage in a conductor moving within a magnetic field. It's applicable to generators. Position your right hand with:

  • Thumb: Representing the direction of motion of the conductor.
  • Index finger: Indicating the direction of the magnetic field (North to South).
  • Middle finger: Showing the direction of the induced current (or EMF).

Again, the fingers must be mutually perpendicular.

Practical Applications

Fleming's laws are fundamental to understanding the operation of:

  • Electric motors: The left-hand rule helps determine the rotational force (torque) generated.
  • Electric generators: The right-hand rule explains how movement within a magnetic field induces a voltage.

The provided reference states that Fleming's law is a set of two rules describing the force and electromotive force on a conductor in a magnetic field. The left-hand rule defines the force's direction, while the BLI law (F=BIL) quantifies it.