Harman Patil (Editor)

FBI mnemonics

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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.

Contents

Other mnemonics exist that use a right hand rule for predicting resulting motion from a preexisting current and field.

'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'

    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
  • 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.

    References

    FBI mnemonics Wikipedia