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Homework Help: Equation for magnetic field

  1. Dec 1, 2008 #1
    Right now I'm looking at this equation for magnetic field force where F=BqVsinΘ where B is magnetic field, q is charge of particle, and V is velocity. However I've seen from some sites that F does not include sinΘ so I was confused on whether which one is right. And also what is Θ in respect to. Is it the angle of the particle direction to the magnetic field?
  2. jcsd
  3. Dec 1, 2008 #2
    This is the vector form of the equation for the force on a charged-particle with some velocity in a magnetic field:

    [tex] \vec{F} = q\vec{v}\times\vec{B}[/tex]

    If your given the velocity and the magnetic field in vector form, i.e. [tex] \vec{v} = \left(v_{x}\right)\hat{x} + \left(v_{y}\right)\hat{y} + \left(v_{z}\right)\hat{z} [/tex], then you can determine the force vector by taking the cross-product. Clear?

    Using just magnitudes of the quantities gives the second-form:

    [tex] F = qvBsin\theta [/tex]

    where [tex] \theta [/tex] is the angle between the velocity, v, and the magnetic field B. This form is used quite often when v and B are constants. Now, if [tex] \theta = \pi/2 [/tex] then the sine term has value 1, so when you do not see the sine term this is what you should assume. Clear?
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