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3 questions about electricity

  1. Jul 31, 2009 #1
    This will be my last electricity topic for a while.

    1. If an electron is "ejected" by the anode of the battery with voltage, in which form of energy has the electron gained? Kinetic Energy or Potential Energy? If it's Potential Energy, how could you physically describe it? I can tell a fast moving electron has a lot of Kinetic Energy because It's moving fast. But how can I describe the Potential Energy of an electron?

    2. In circuits, how is voltage related to the electric field? Why must work be done against the electric field? Does the battery have an electric field? If so, what is the direction of it? Is it from negative to positive or vice versa?

    3. How come only moving charge produces a magnetic field?
  2. jcsd
  3. Jul 31, 2009 #2
    Sigh...37 looks...No replies. What is wrong with my post? :uhh:
  4. Jul 31, 2009 #3


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    Homework Helper

    You're too impatient, that's what's wrong :wink: 37 views is nothing to get worried about.
    1. An electron that leaves the negative terminal of a battery won't be moving at high velocity right away, so that rules out kinetic energy. It has electrical potential energy. And there is no physical description of potential energy that corresponds to "it's moving fast" for kinetic energy. The best you can do is note that the electron will be pulled toward a region where it would have lower potential energy.

    2. The electric field is the gradient of voltage - that is, electric field is how much the voltage changes per unit distance. An electric field tries to push charges in some direction, so if you want to move the charges in the other direction, you need to do work to overcome the electric field's push. A battery does produce an electric field, and I believe it goes from positive to negative, as electric fields always do.

    3. That's just the way the world works. Why would you think a stationary charge should produce a magnetic field? You could perhaps try to go with the relativistic explanation, in which a magnetic field is produced by relativistic transformations of the electric field (kind of like time dilation and length contraction), but that could just as easily become really confusing.
  5. Jul 31, 2009 #4
    How does a battery produce an electric field though? And if electrons go from negative to positive, then why do you need to do work against the electric field going from positive to negative?
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