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Homework Help: Physics Help Please? Basic ?

  1. Jun 24, 2008 #1
    Here is the question that I'm given:

    Consider a circuit with a capacitor, battery, wire, and bulb. Describe the source(s) of charge during:

    1. capacitor charging
    2. capacitor discharging

    What is the cause of charge motion during capacitor charging?

    Using the analogy of the air capacitor, what do you think might be the cause of charge motion during capacitor discharging?

    My solution: I thought that the battery in a circuit provided the energy for the charge to move through, but would this be a correct answer to the first question? Wouldn't the charge come from the discharged capacitor when the capacitor is discharged? For the second question, "What is the cause of charge of motion during capacitor charging?" I have no idea what to write. I don't even get what the question is asking. For the last question, I don't understand it either. I just need some help in understanding all of this!

    3. The attempt at a solution
  2. jcsd
  3. Jun 24, 2008 #2
    Think of the capacitor as two sheets of metal, separated by a bit of air.
    If the capacitor is charged, then one sheet will hold positive charges (or lack of negative charges) and the other sheet will hold negative charges. What do you know about when these two types of charges meet? They attract each other! But since the charges cannot go through the air, they have to go through the rest of the circuit.
    If the capacitor is being charged then something must 'push' the charges back into the sheets so they don't flow back to each other (through the circuit). The battery is ofcourse what supplies the energy to do this.

    Now consider what happens when the battery is switched off. What are the charges going to do? So what is the source of energy to discharge the capacitor?
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