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Homework Help: Magnitude of force on a Dust Particle

  1. Nov 25, 2009 #1
    1. The problem statement, all variables and given/known data
    A magnet produces a 0.40 T field between its poles, directed horizontally to the east. A dust particle with charge q = -8.0×10-18 C is moving vertically downwards with a speed of 0.30 cm/s in this field. Whilst it is in the magnetic field, the dust particle is also in an electric field of strength 1.00×10-2 V/m pointing to the north.

    (a) What is the magnitude and direction of the magnetic force on the dust particle?
    (b) What is the magnitude and direction of the electric force on the dust particle?
    (c) What is the magnitude of the net force on the dust particle?
    2. Relevant equations

    FB= qvBsinθ
    E= FE/q

    3. The attempt at a solution
    For part a) i got 9.6x10^-21N to the north according to the right hand rule
    For part b) i got a magnitude of 4.44x10^-3N but i'm not sure how to find the direction of the force.
  2. jcsd
  3. Nov 25, 2009 #2


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    Science Advisor
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    Gold Member

    What is the direction of the force due to the electric field? Draw a diagram of the two forces, then add them as vectors to find the resultant.
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