FBI mnemonics

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Left hand rule LeftHandOutline.png
Left hand rule
Alternate representation of LHR ManoLaplace.svg
Alternate representation of LHR

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 [1] and Faraday's law of induction.

Contents

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'

'IBF'

Right-handed alternate - 'IBF'. Rechte-hand-regel.jpg
Right-handed alternate - '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')

Prediction of direction of field ('B'). Right hand rule.png
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

VectorLeft-Motor or Right-GeneratorLeft-Motor or Right-GeneratorLeft-Motor or Right-GeneratorRight-Motor or Left-GeneratorRight-Motor or Left-GeneratorRight-Motor or Left-Generator
B or FieldFirst or IndexThumbFingers or PalmFirst or IndexThumbFingers or Palm
I or Current (+ to - flow)Fingers or PalmFirst or IndexThumbThumbFingers or PalmFirst or Index
Force, Motion, or ThrustThumbFingers or PalmFirst or IndexFingers or PalmFirst or IndexThumb

References

  1. "Fleming's Left Hand Rule". Shiken.ai. 5 September 2023. Retrieved 3 February 2024.[ permanent dead link ]