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Homework Help: Right hand rules explanation

  1. Jul 30, 2008 #1
    1. The problem statement, all variables and given/known data



    This is not problem. I just having trouble understanding the basics. Please just tell me right away, don't 'assist!'

    I trying to understand the right hand rule. Here are to images I found to illustrate my problem. Apparently, right hand rule 2 tells you to grip a long wire, and to find the magnetic field from that. Okay so if I grip a wire with current going upwards, the magnetic field is into the page, and if the current is going downwards, then magnetic field is out of the page.

    But you do you explain these two picture?
    In the first picture, the magnetic field is on the 5A wire is apparently ...downwards? How? And the magnetic field on the 3A wire is downward? How is that work? First they dont tell you which way the current is going, up or down. Secondly, the answer is not 'into the page' or 'out of the 'page.' It is 'upwards' or 'downwards,' how come?

    The second image is mind baffling. What is going on? How can two wires coming out the page have different magnetic fields?
    Last edited by a moderator: Apr 23, 2017
  2. jcsd
  3. Jul 30, 2008 #2


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    Homework Helper

    I'm not sure what you mean by these statements, but they don't sound right, and I think they are the source of your confusion. A wire does not have a single direction of the magnetic field; the magnetic field direction depends on what point you're talking about.

    If a current is going upwards (towards the top of a page), the magnetic field is not simply "into the page". The current creates a magnetic field everywhere; at points to the right of the current is is into the page; to the left of the current it is out of the page; behind the current it is to the left; in front of the current it is to the right. (At other points it is at an angle.)

    If you hold your right hand with the thumb upwards and rotate your hand around the thumb, you can see these directions are indicated by your fingers as you move your hand around (with your thumb always kept pointing upwards).

    So if you look at your first figure, the question is not,"What is the direction of the magnetic field of the 5A wire?" because there's not enough information given to get a specific direction.

    Instead, What is the direction of the magnetic field of the 5A wire at point P? What is the direction of the magnetic field of the 5A wire at the position of the 3A wire? Those two questions have different answers. Do you see what the answers are?

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    Last edited by a moderator: Apr 23, 2017
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