Left-hand Rule: Unreliable or Misinterpretation?

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Discussion Overview

The discussion revolves around the concept of the left-hand rule, particularly Fleming's left-hand rule, and its reliability compared to the right-hand rule. Participants explore the definitions, applications, and conventions associated with these rules in the context of electromagnetism and motor functions.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question the reliability of the left-hand rule, suggesting it may be a misinterpretation or an impersonation of the right-hand rule.
  • Others explain Fleming's left-hand rule as a method for determining the direction of force in a magnetic field, emphasizing its utility in applications like motors.
  • A participant notes the existence of both left-hand and right-hand rules in various texts, implying a lack of consensus on which is preferable.
  • One participant attributes the confusion surrounding these rules to historical conventions, mentioning Benjamin Franklin's influence on the definitions of current flow.
  • Another participant describes the left-hand rule in detail, explaining how it relates to the Lorentz force and the reversal of directions affecting the force outcome.
  • A mnemonic is provided by a participant to help remember the associations of fingers in Fleming's left-hand rule: Thumb for force, first finger for magnetic field direction, and second finger for current.

Areas of Agreement / Disagreement

Participants express differing views on the reliability and interpretation of the left-hand rule versus the right-hand rule. There is no consensus on which rule is more valid or widely accepted, indicating ongoing debate and uncertainty.

Contextual Notes

Participants highlight the dependence on conventions and definitions, suggesting that interpretations may vary across different educational resources. The discussion also reflects unresolved questions about the historical context and implications of these rules.

anil
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Is there some thing really called left-hand rule? I have heard my teacher say it but she is not reliable. I have heard of right hand rule(RHR)? Or is it imporsonation of RHR to go with flow of electron instead of protons
 
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Fleming's left hand rule, for working out the force effect of a current and field. Using your left hand, first finger points at the direction of the field, second finger the conventional current, and thumb gives direction of force. Kinda useful for motors and stuff.
 
I have books that teach the Left-Hand Rule, and others that teach the Right-Hand Rule.

Isn't this all Ben Franklins fault?
 
It is a matter of convention, which hand or what kind of screw to use to represent result of vector products. Various texts refer to various hands and screws, but they all agree with each other.

Say, in my high school left hand rule was the one which gives you the direction of Lorents force on moving in magnetic field charge. If the field is enetering your open left palm, and the positive charge is moving in the direction of 4 fingers, then the Lorents magnetic force on the charge is directed along the thumb. Reversing anyone quantity (field direction, or velocity direction, or charge sign) reverses force direction. Right screw rule usually refers to direction of magnetic field generated by moving charge. If a positive charge is moving say from you into this display screen, then the magnetic field it generates is circular field going closckwise around the charge.

Both rules (or their various versions) come from definition of magnetic field being just a vector product of velocity of observer moving by stationary electric field times electric field: B' = [vxE]gamma/c^2 (prime refers to moving system, where observer is. In non-moving system vxE=0xE=0 as you can see, thus no "magnetic term" is generated, B=0 when you are not moving versus electric field or electric charge).
 
FBI

Orginally posted by FZ+
Fleming's left hand rule, for working out the force effect of a
current and field. Using your left hand, first finger points at the direction of the field, second finger the conventional current, and thumb gives direction of force.

Here is an easy way to remember which finger represents what.
Thumb : F (force)
First finger : B (direction of the magnetic field)
Second finger : I (Current)
 

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