FBI mnemonics
The various FBI mnemonics (for electric motors) 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.
Configuration, using the right hand
Other sources use the right hand to predict force, though the fingers used vary:
'FIB'
- Thumb = F ("thrust")
- Index finger = I or V
- Middle finger ("Birdie") = B
'IBF'
In this alternative, some versions recommend not extending the middle finger, but instead imagining the force coming from the palm of the hand.
- Thumb = I or V
- Index finger = B
- Middle finger = F
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 ('B') produced by current ('I') traveling through a wire.
Symmetry
| Vector | Left-Motor or Right-Generator | Left-Motor or Right-Generator | Left-Motor or Right-Generator | Right-Motor or Left-Generator | Right-Motor or Left-Generator | Right-Motor or Left-Generator |
|---|---|---|---|---|---|---|
| B or Field | First or Index | Thumb | Fingers or Palm | First or Index | Thumb | Fingers or Palm |
| I or Current (+ to - flow) | Fingers or Palm | First or Index | Thumb | Thumb | Fingers or Palm | First or Index |
| Force, Motion, or Thrust | Thumb | Fingers or Palm | First or Index | Fingers or Palm | First or Index | Thumb |