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Homework Help: Current and Drift Velocity

  1. Jan 23, 2004 #1
    I dont even know where to begin on this one.

    SPEAR, a storage ring about 72.0 m in diamter at the Stanford Linear Accelorator, has a 20.0 A circulating beam of electrons that are moving at nearly the speed of light. How many electrons are in the beam???

    My thoughts, hmmmm. Nothing I can think of even makes sense. If they are traveling near the speed of light then they must be only moving in one direction and not at random, the only way this could happen is if the size of the storage ring were the size of an electron, but since there is not a known size of an electron this does me no good.

    Go ahead tell me I'm an idiot, but could you help me along the way.

  2. jcsd
  3. Jan 23, 2004 #2


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    You may be an idiot. :wink:

    Current is defined as the amount of charge that pass a certain point in one second, correct?

    What you need to do is to calculate the average time taken for an electron to traverse the circumference of the ring, and then multiply by current to get charge in coulombs. Easy going from then on.
  4. Jan 23, 2004 #3

    I'll try that

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