Flemings Left hand and Right hand rule


Two of the most useful tools for understanding electromagnetism right at the end of your arms. These convenient appendage helps to understand the interaction between electricity and magnetism via the Right Hand Rule and the Left Hand Rule.

If a current carrying conductor placed in a magnetic field, it experiences a force due to the magnetic field. On the other hand, if a conductor moved in a magnetic field, an emf gets induced across the conductor (Faraday’s law of electromagnetic induction).

John Ambrose Fleming introduced two rules to determine the direction of motion (in motors) or the direction of induced current (in generators). The rules are called as Fleming’s Left hand rule is mainly applicable to electric motors and Fleming’s Right hand rule is mainly applicable to electric generators.

These rules do not determine the magnitude but instead show the direction of any of the three parameters (magnetic field, current, force) when the direction of the other two parameters is known.

Flemings left hand rule

Whenever a current carrying conductor is placed in a magnetic field, the conductor experiences a force which is perpendicular to both the magnetic field and the direction of current.

According to Flemings left hand rule,

if the thumb, fore-finger and middle finger of the left hand are stretched to be perpendicular to each other as shown in the illustration at left, and if the fore finger represents the direction of magnetic field, the middle finger represents the direction of current, then the thumb represents the direction of force. Flemings left hand rule is applicable for motors.

Fleming’s left hand rule

Flemings left hand rule with FBI.

Here, F for Force, B is the symbol of magnetic flux density and I is the symbol of Current. Attribute these letters F,B,I to the thumb, first finger and middle finger respectively

A portion of a conductor, length ‘L’ is placed vertically in a uniform horizontal magnetic field of strength ‘H’, produced by two magnetic poles N and S. If the current ‘I’ is flowing through this conductor, the magnitude of the force acting on the conductor is:


Flemings Right hand rule


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