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Homework Help: Help on 2 problems on magnetism

  1. Jun 30, 2004 #1
    1. A 10.9E-6 particle with mass 2.80E-5kg moves perpendicular to a 1.01 magnetic field in a circular path of radius 26.6m. How fast is the particle moving? How long will it take the particle to complete one orbit?

    I used v=rqB/m and got the wrong answer for velocity and I have no idea how to get the time.

    2. A high voltage power line carries a current of 110A at a location where the earth's magnetic field has a magnitude of 0.45E-4T and points to the north, 72 degrees below the horizontal. Find the direction and magnitude of the magnetic force exerted on a 210m length of wired if the current in the wire flows in the following directions.
    a. horizontally to the east
    find the force and degree and direction of the horizontal
    b. horizontally toward the south
    find the force and direction (north, south, east, west)

    I used F=ILBsintheta
    and got the incorrect answer
    Can anyone show me what to do...tht would be very helpful
  2. jcsd
  3. Jun 30, 2004 #2


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    Science Advisor

    1. Use v=rqB/m and get the right answer. Seriously. You probably are not using the physical quantities correctly. I notice you say a 10.9e-6 particle and a 1.01 magnetic field, with no dimensions. So I'm guessing you have a problem with dimensions. Physics is much more than just finding a formula and plugging numbers in. You have to know what the formulas mean.

    Also, are you seriously saying that if you know the radius and speed in a circular orbit you cannot derive the orbit time? Here's an analogous situation: you travel 60 mph; how long does it take you to travel 10 miles?
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