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[1] and Faraday's law of induction.

Left hand rule
Alternate representation of LHR

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 Thumb represents F - Thrust (or resulting Motion).
  • The First finger represents B - Field.
  • The Second finger represents I or V - Current (in the classical direction, from positive to negative).

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'
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.

  • Thumb = I or V
  • Index finger = B
  • Middle finger = F

Other frequently confused rules

Prediction of direction of field ('B')
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.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.