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Homework Help: Magnetic fields ahhh!

  1. Feb 26, 2004 #1
    Here's my problem:

    A particle with charge 4.5E-19 C travels in a circular orbit with radius .465 m due to the force exerted on it by a magnetic field with magnitude 1.7 T and perpendicular to the orbit.

    a) What is the magnitude of the momentum p of the particle?
    I used the equation R=(mv)/(qB) and calculated mv (linear momentum) to be 3.6E-19 kg*m/s.

    b) What is the magnitude of the angular momentum L of the particle?
    Herein lies the rub! Angular momentum = v/R = qB/m
    I don't know velocity or mass independently, only their product (mv). So how do I calculate angular momentum?

    Thanks for any help!
  2. jcsd
  3. Feb 26, 2004 #2
    angular speed: ω = v/r

    angular momentum: L = r x p

    Since your particle is moving in a circle, it's linear momentum vector p is always perpendicular to the position vector (radius) r so the angular momentum is simply the product:
    L = rp = rmv
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