1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Left Hand Rule

  1. Nov 15, 2009 #1
    Throughout the electric force/field and magnetism unit, there's always a rule that involved using the left hand and the right hand. I'm a bit confused on how to apply the rules because of the units are applied to different fingers. If someone could give me an explanation on it, that'd be great.

    Another question: How do you find which end is North and which end is South in a current?
  2. jcsd
  3. Nov 15, 2009 #2


    User Avatar
    Science Advisor
    Gold Member

    To the best of my recollection, all vector rules and directions of note require that only right-hand rules are used. The only time I have seen left-hand rules used are in left-handed materials where both the permittivity and permeability are negative. These are not encountered naturally.

    Current does not have a north or south end. Current is made up of electrons, point charges, that act as monopoles, they do not have two poles to reference as north and south.
  4. Nov 15, 2009 #3
    After looking at it for a while, I kind of understood the concepts.

    My apologies for the second question. I was picturing a coil in a circuit when I typed this.
  5. Nov 16, 2009 #4
    Hi Soph

    Thanks for giving me the opportunity to try and explain this. I am only a novice at electromagetics, but I have just recently gone over the same ground of questioning that you have raised in this question .... so here we go... can I do this??

    Say your right hand is out in front of you with palm up ...- thumb out to the right ... -and your fingers curled up and back towards you. Say there is a horizontal conductor sitting in that right palm of your hand with conventional current (opposite to electron flow) flowing from left to right. That means you would draw a plus sign on the left of this conductor and draw a negative sign on the right of this conductor ... right ??? Now here is the thing - the FLUX will flow in the direction of your curled fingers. And notice this also: - in a coil configuration the FLUX flows from the NORTH towards the SOUTH pole on the outside of the coil and from South towards the North on the inside of the coil.

    I can understand this sounds complicated. This is where a picture would come in handy. It is hard to explain this in words.

    Anyway thanks for giving me a try at it.o:)
  6. Nov 16, 2009 #5
    Thanks Leon. I've been touching up on that subject, and I had some doubts over that, but I understand it better now.
  7. Nov 17, 2009 #6
    A few sources, one such example is the New York State Regents Physics curriculum, refer to "electron flow" in all cases, and never refer to conventional current, therefore the magnetism unit has left hand rules instead of right hand rules.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook