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Homework Help: A singly charged positive ion with a mass of 6.68x10-27 kg moves clockwise with a sp

  1. Apr 9, 2008 #1
    1. The problem statement, all variables and given/known data

    A singly charged positive ion with a mass of 6.68 x 10^-27 kg moves clockwise with a speed of 1.10 x 10^4 m/s in a circular path with a radius of 2.00 cm. Find the direction and strength of the magnetic field. (Hint: The magnetic force exerted on the ion is the force that maintains circular motion, and the speed of the ion given is its tangential speed.)

    _____ T

    2. Relevant equations

    F = ma and since the particle travels in a circle, F = mv² / r which is the magnitude of the magnetic field.

    3. The attempt at a solution

    F = 6.68•10^-27 kg•(1.10•10^4 m/s)² / 0.2m

    but the answer is wrong.
  2. jcsd
  3. Apr 9, 2008 #2


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    What is the formula for finding the force exerted by a magnetic field on a charged particle?
    When you find that formula, that provides the centripetal force to keep it in a circle.
  4. Apr 9, 2008 #3
    . . . i obviously have no idea ?
  5. Apr 10, 2008 #4


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    force exerted by a magnetic field on a charged particle?= BQv

    B=magnetic flux density
    Q=charge of particle
    v=velocity of particle.
  6. Apr 10, 2008 #5
    Lol maybe you should've done a bit more research, at least to figure out the needed formulas. Wikipedia is often a good source.
    F=ma....How would you go about finding the Acceleration? Are you finding the Accel of the Ion? And if so, does it even HAVE an acceleration?
    Last edited: Apr 10, 2008
  7. Apr 10, 2008 #6
    yes it does have an acceleration....but perpendicular to the velocity =)
  8. Apr 10, 2008 #7
    Perpendicular? I don't even know how that happens. Does "Perpendicular to the Velocity" just mean the object is turning? How does Accel go about being perpendicular to Velocity? try to give an example? Because I assumed that the object maintained the same speed (1.10 x 10^4 m/s), in which case the acceleration would be 0.
  9. Apr 10, 2008 #8
    The centripetal force causes the acceleration to be inward towards the center of the circle. He's right that the instantaneous velocity is tangential to the acceleration.

    Anyway, you don't need to find the acceleration. Couple the formula that you know with rock.freak667's formula.
  10. Apr 10, 2008 #9
    yeah, I was gonna say that the other formula makes more sense.
    So much about Physics seems arbitrary right now. Like, gravity. There's no real reason why 2 masses attract one another.
    Last edited: Apr 10, 2008
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