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Expression for magnitude of magnetic force

  1. Feb 10, 2015 #1
    1. The problem statement, all variables and given/known data
    A particle with charge q moves with velocity v near a long, straight wire which has a current I flowing through it which generates magnetic field B. Give an expression for the magnitude of the force on this particle in terms of q, v = | v | and the magnitude of the magnetic field strength B. Make sure you define any other variables that you introduce.

    2. Relevant equations
    F = q(v x B)

    3. The attempt at a solution
    Could it be as simple as just quoting F = q(v x B)? I feel as though I may be missing something as this would seem a little too straight forward.

    Cheers guys.
     
  2. jcsd
  3. Feb 10, 2015 #2

    lightgrav

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    no, that writes it in terms of the velocity vector and the magnetic field vector.
    They want you to write it in terms of the scalar speed and the magnetic field strength (scalar).
    (hint: you WILL need to introduce a new variable that you'll need to define)
     
  4. Feb 10, 2015 #3
    Thanks a lot for the reply!
    Is it somehow related to the formula for magnetic field strength at a given distance from a wire: B= [PLAIN]http://scienceworld.wolfram.com/physics/pimg170.gifi [Broken] / 2pi r? Im struggling to see from my books what else could be relevant.
     
    Last edited by a moderator: May 7, 2017
  5. Feb 10, 2015 #4

    lightgrav

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    they don't want your "Making B" equation ... that would write the Force in terms of I, not B.
    what does that little "x" in your formula mean?
     
  6. Feb 11, 2015 #5
    Ahh so you could take the dot product rather than the cross product of the vectors and theta would be the new variable?
     
  7. Feb 11, 2015 #6

    lightgrav

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    multiplication of scalars is not really a "dot product", it is simply multiplication.
    A "dot product" multiplies the parallel components of 2 vectors, yielding a scalar.
    This "cross product" multiplies the 2 vectors' perpendicular components, yielding a 3rd (perp) vector.
     
  8. Feb 12, 2015 #7
    This is what I got, would appreciate some input:

    F = qvBsin(theta)
     
  9. Feb 12, 2015 #8

    lightgrav

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    yes, good ... but since θ is a new variable, you need to define it (as they explicitly stated)
     
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