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Homework Help: Calculate current in a wire

  1. Feb 12, 2015 #1
    1. The problem statement, all variables and given/known data

    Suppose the particle has a charge q = 2.5 μC and is moving with a velocity of magnitude v = 1.0 × 103 m s−1, in a direction parallel to the wire and in the same direction as the current. The particle is at distance d = 1.5 mm from the wire and experiences a force of magnitude 1.0 × 10−6 N. Calculate the current in the wire. Draw a diagram to indicate the direction of the force on the particle.

    2. Relevant equations

    F = qvBsin

    3. The attempt at a solution

    I really have no idea how to tackle this. I'm not even sure that I'm using the correct equation. This question follows another which asks for an expression for the magnitude of the magnetic field strength, B, and just assumed that this eqn would apply here.

    We have F, q, v and d, but not sure how we get i, and neither B to be honest. Some hints and advice would be greatly appreciated!
  2. jcsd
  3. Feb 12, 2015 #2


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    Staff: Mentor

    You Relevant equation is relevant :) But you'll need more. Check your text, notes, or online for an expression that gives the magnitude of the magnetic field for a current-carrying wire. Google: "magnetic field of a current carrying wire" or "Magnetic fields of currents".

    You may also want to review the right-hand rule for magnetic field direction due to a current or moving charge.
  4. Feb 12, 2015 #3
    Thanks for the reply. Am I getting warmer here:

    By using the value for B = μ0 (i) / 2 π r = 4πx10-7 (i) / 2 π r

    we now have current, i, in the eqn F = qvBsinθ, and can now solve for i? Will sinθ be sin90?
  5. Feb 12, 2015 #4


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    Staff: Mentor

    What does the right-hand rule tell you about the direction of the magnetic field at the location of the particle?
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