Fleming's Left Hand Rule

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Understanding Fleming’s Left Hand Rule

• Fleming’s Left Hand Rule is a simple rule to determine the direction of force on a current-carrying conductor placed in a magnetic field.
• It is called the ‘Left Hand’ rule because it uses the left hand to represent the three mutually perpendicular directions.
• The thumb represents Motion (Force), first finger Field (Magnetic field), and second finger Current.

The Three Fingers

• Thumb (Motion): The direction in which the conductor will move (Force), subject to the forces acting on it (gravity, friction etc.).
• First finger (Field): Represents the direction of the magnetic field, from North to South.
• Second finger (Current): Points in the conventional direction of electric current, from positive to negative.

Application of the Rule

• Arrange your left hand so that fingers are at right angles to each other.
• Stretch out the thumb, first finger and second finger of your left hand such that they are mutually perpendicular.
• Point your first finger in the direction of the field (From North to South).
• Point your second finger in the direction of current.
• Your thumb now points in the direction of the motion or force on the conductor.

Important Considerations

• Fleming’s Left Hand Rule is specifically for motors where mechanical movement results from electric and magnetic fields.
• It is not to be confused with Fleming’s Right Hand Rule, which applies to generators and dictates the direction of induced current when a conductor cuts through magnetic field lines.

With this simple and interesting mnemonic device, one can quickly and intuitively figure out the direction of the force on a current-carrying conductor in a magnetic field.