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Magnetic Field and Charge

  1. Jul 15, 2007 #1
    1. The problem statement, all variables and given/known data
    Consider a magnetic field in the z direction. Two particles are moving perpendicular to this magnetic field, that is, they are both moving in the x-y plane. It is observed that the particles are both deflected by the magnetic field and they are deflected in opposite directions. Which of the following scenarios can account for this behavior?

    True False they were initially moving in the same direction, but they have the same charge
    True False they were initially moving in opposite directions, but they have the same charge
    True False they were initially moving in opposite directions, but both are uncharged
    True False they were initially moving in the same direction, but one is uncharged
    True False they were initially moving in opposite directions, but they are oppositely charged
    True False they were initially moving in the same direction, but they are oppositely charged


    3. The attempt at a solution
    My answers are in bold but the computer says they are wrong, here is my reasoning for my answers:
    1) same charge particles repel one another
    2) same as 1 so they will go in opposite directions
    3) uncharged particles have no reaction
    4) Again, one uncharged particle will have no reaction with a charged particle
    5) Opposites will always attract one another, so they cannot go in opposite directions
    6) same as 5, the opposites will pull each other together

    Can any1 help me with what im doing wrong?
     
  2. jcsd
  3. Jul 16, 2007 #2

    danago

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    I think perhaps you are to assume that the repulsive/attractive behaviour of the particles is negligiable, and answer in terms of the effect of the magnetic field only, remembering that a charge moving through a magnetic field is subject to a force.

    Have you ever been shown the "right hand rule"?
     
    Last edited: Jul 16, 2007
  4. Jul 16, 2007 #3
    no what is the right hand rule? so basically ur saying to ignore the charges of the particles? but uncharged particles dont move...
     
  5. Jul 16, 2007 #4

    danago

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    Gold Member

    When a charge moves through a magnetic field, it experiences a force. You know that, right?

    The actual direction of the force is perpendicular to both the magnetic field and the direction of movement of the charge, right? Basically, if you take your right hand, and point your THUMB in the direction of the flow of POSITIVE charge, and point your other fingers in the direction of the magnetic field, the face of your palm will point in the direction of the applied force on the charge.

    http://cache.eb.com/eb/image?id=254&rendTypeId=4

    Take a look at that picture, it shows the use of the right hand rule. Its just a simple way of remembering the direction of a force on a charged particle in a magnetic field, without having to go into the mathematics of it and actually work it out.
     
    Last edited: Jul 16, 2007
  6. Jul 16, 2007 #5
    okay, but i dont quite understand how this relates to the question. the questions speaks of two charges either moving in the same or opposite directions, and do the charges come into play at all?
     
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