FBI mnemonics


The various FBI mnemonics show the direction of the force on a conductor carrying a current in a magnetic field as predicted by Fleming's left hand rule for motors and Faraday's law of induction.
Other mnemonics exist that use a right hand rule for predicting resulting motion from a preexisting current and field.

Configuration, using the left hand

'FBI'

The left hand is held with the thumb, first finger and second finger mutually at right angles.
  • The Thu'mb represents F - Thrust.
  • The F'irst finger represents B - Field.
  • The Second finger represents I or V - Current.

Configuration, using the right hand

Other sources use the right hand to predict force, though the fingers used vary:

'FIB'

'IBF'

In this alternative, some versions recommend not extending the middle finger, but instead imagining the force coming from the palm of the hand.

Other frequently confused rules

Prediction of direction of field ('B')

The rules above are usually used to predict 'F' based upon 'B' and 'I' - the force on a moving charge when moving through a field, whether or not the charge is carried in a wire. However, this rule should not be confused with a different right hand grip rule for the prediction of the direction of a field produced by current traveling through a wire.