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Homework Help: What is a resistor?

  1. Jun 12, 2012 #1
    and what is its purpose? what does a resistor actually do?

    My understanding is that electrical resistance is sort of like electrical friction,

    or imagine sitting in a car, with your hand out of the window, as the car speeds up, you feel more resistance against your hand, and it takes more energy to hold your hand there as the car gets faster and faster.

    the wind in this case is the current, and the hand is feeling the resistance.

    Also as the current gets higher, the more electrical resistance it encounters, to get the amount of current 'under control' so to speak so that the resistance doesnt get out of hand, a resistor sort of 'eats' or 'resists' the electrical current, so there isnt too much current and as a result there isnt too much electrical resistance.

    Does this make any sense? Am i correct on this?

    Also Electrical potential energy is the amount of energy it takes to move charges across a circuit,and that energy is lost while the charges move across the circuit, that energy is lost in 2 ways, its either used up ( converted into light and heat if there is a bulb present) or that energy is lost just carrying the electrical charges over the circuit.

    Is this true also?
  2. jcsd
  3. Jun 12, 2012 #2


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    Think of a wire made of something that is a perfect conductor. Current can run through it and there is no loss --- no heat generated in the wire because there is a current running through it.

    Now add impurities that slow some of the electron flow. That is resistance. It causes heat to be generated in the wire and requires power to "push" the current through the wire.

    Resistors control the amount of current in various parts of electrical circuits.

    Conservation of energy is not valid on cosmological scales but it IS valid on local scales such as an electrical circuit, so the energy is NOT lost, it is always converted into something else (usually heat or light).
  4. Jun 12, 2012 #3
    Ah...so the resistors are like dams controling the electric current!!!

    hm...so some of the energy i suppose is used in moving those charges themselves , either that or it can be converted into heat/light via a load (for example a lightbulb) and THIS is what is responsible for the electric potential difference Yes?

    (correct me if my usage of the word load isnt right)
  5. Jun 12, 2012 #4


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    Well, that's not a terrible analogy.

    No, you have that backwards. It is the potential difference that drives the current, regardless what form the energy expenditure of the current takes.
  6. Jun 12, 2012 #5
    ok so here is a question, if there is no outlet for the energy in a charge, and it returns to negative terminal, does it still lose all that energy? In other words if there is just a circuit by itself, and there is no lightbulb, does it still lose the energy?
  7. Jun 12, 2012 #6


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    If there is an open circuit ("no lightbulb"), the the electrical potential energy just sits there, exactly as does water behind a dam when the spill-gates are closed.
  8. Jun 12, 2012 #7
    ahhh.... thanks!
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