Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Where does current go?

  1. Jun 29, 2011 #1
    Current and charge do not increase or decrease or get used up when going through a wire or other device. The amount of charge that goes in at one end comes out at the other end.

    Where does the current go then, when I run electrical devices? If it is not used up when I turn on a light bulb or use the TV, where does it go?
  2. jcsd
  3. Jun 29, 2011 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    It's called a ground for a reason.
  4. Jun 29, 2011 #3


    User Avatar
    Staff Emeritus
    Science Advisor

    Current is the flow of charges (in this case Electrons) through the conductor. Like you said the amount of current is the same at the beginning and end of the circuit. The current (charges) never go anywhere, they are always there. Imagine you have a pipe of water with a water pump that pumps it around the pipe in a circle. The water never goes anywhere but around the pipe, but the pump has to perform work on the water to keep it flowing because of resistance.

    If you increase the resistance of the pipe then you have less water flowing by a particular point per second than the pipe with less resistance. Similarly, increasing the resistance of the circuit causes less current to flow at all.

    Depending on what you mean by ground, that could be mean that it is the return wire for the circuit or that it is the safety wire in a household circuit that only transmits current to ground in a fault situation.
  5. Jun 29, 2011 #4
    So then what do electric companies charge you for? The voltage they provide that is necessary for the current?
  6. Jun 29, 2011 #5


    User Avatar
    Staff Emeritus
    Science Advisor

    They charge you because it takes work to produce electricity. To produce the voltage that determines the current in a circuit you have to use energy. Typically power plants use fossil fuels or nuclear power to heat water which then turns a steam turbine. The turbine turns a generator which produces the power. The key here is that when the generator is turning there is resistance to it. The more power drawn from the generator the greater the resistance to the generator turning and the more power has to be input to the generator. You are paying for the fuel, infrastructure, employees, ETC.
  7. Jun 29, 2011 #6


    User Avatar
    Gold Member

    The work done. It does power your lights. Energy is flowing into your house as useful electricity and leaving as waste heat.
  8. Jun 29, 2011 #7
    Yes it does. That's the whole idea.
  9. Jun 29, 2011 #8


    User Avatar

    Staff: Mentor

    No, it really doesn't. The current at any place in a continuous, brancless circuit is the same.
  10. Jun 30, 2011 #9
    Uh, no. A resistive device within the circuit will reduce current flow.
  11. Jun 30, 2011 #10


    User Avatar
    Science Advisor
    Homework Helper

    Drakkith's answer is just about perfect.

    Current is the rate of flow.

    In this case, the things that are moving (or flowing) are electrons (and the electrical charge associated with those electrons). In an electric circuit, especially if it's AC, those electrons aren't actually going anywhere - they're just moving around in your wires.

    You're paying to have those electrons moved for you, not for the electrons. Just like in Drakkith's example, where the water is yours, but you're paying to run the pump that moves the water around for you.
  12. Jun 30, 2011 #11


    User Avatar
    Staff Emeritus
    Science Advisor

    Yes, the current throughout the circuit will be reduced, correct?
    The current isn't going anywhere or being used up. There is simply less because of the resistance. I think thats what both of you are saying.
  13. Jul 1, 2011 #12
    Well, it IS being used up, in a sense. It HAS to be, else one would have perpetual motion with infinite energy draw.
    The key is "conversion" A specific amount of current flow is reduced, by conversion, to, say, heat or light. Thus there IS less current.
  14. Jul 1, 2011 #13


    User Avatar
    Gold Member

    No, the heat or light is produced by the work done at the power station in moving the electrons around the circuit loop. To get more current to produce a brighter light, the power station has to do more work. The current isn't used up at all. What's used is the work being done at the power station. That's what you are paying for (well, that and all those wires that the power company has to maintain).
  15. Jul 1, 2011 #14
    I would confidently say that my 1500 watt electrical space heater is, in fact, initially reducing current at IT'S LOCATION, not the power station.
    The "power station" must then ramp-up current flow to compensate for the losses at my space heater's location.
    Thus the "bill"
    Last edited: Jul 1, 2011
  16. Jul 1, 2011 #15
    current is loosly bound electrons moving along from atom to atom in a conductor...they don't "disappear....

    Perhaps what you are thinking about is energy (power)...THAT is what is being consumed by electrical appliances....electrons don't disappear in loads anymore than they are produced at generating devices.

    palladin: try reading about Kirchoff's current law.
  17. Jul 1, 2011 #16


    User Avatar
    Science Advisor
    Gold Member

    When your heater is switched off, there's zero current through it, so when it's switched on it's increasing the current, not reducing it. But it does cause a small drop in voltage, which the power station has to compensate for.
  18. Jul 1, 2011 #17
    I never said or suggested that the actual electrons are "consumed"
    Rather, what I am saying is that the energy during the event most cetainly is(rather converted) to heat, light, etc...
    That event requires a reduction in current flow.
  19. Jul 1, 2011 #18

    where do you think the electrons go??

    you have energy and current confused.
  20. Jul 1, 2011 #19
    Look, it's very simple: Resistive devices in an electrical circuit DISSIPATE energy.
    This action necessarily results in a quantifiable reduction in current flow.
  21. Jul 1, 2011 #20
    OK, everyone. A reduction in electron "flow" DOES NOT in any way mean a loss of the specific electrons themselves...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook