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Simple amperage question

  1. Feb 7, 2008 #1
    Someone told me that "low resistance leads to high amperage".

    I said that higher resistance is actually what leads to high amperage.

    Which is correct?
     
  2. jcsd
  3. Feb 7, 2008 #2

    chroot

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    "Amperage" is not a word. The proper word is 'current.'

    If you apply some specific potential difference to two different loads, the load with the lower resistance will carry the greatest current. This is Ohm's law. It sounds to me like your understanding is incorrect.

    - Warren
     
    Last edited: Feb 7, 2008
  4. Feb 7, 2008 #3
    The former is correct. Sort of.

    For example, if you chose a wire with twice the diameter, its cross section will be four times higher (assuming the wire is round). It will also have four times less resistance. It will be able to handle four times the current. Similarly, after getting four wires each with a diameter half as thick as that first wire, you can connect them in parallel and get a similar resistance.

    The catch with the statement "low resistance leads to high [current]" is that a material may have low resistance and yet not have any current flowing through it. You must consider more of the situation, such as what is feeding current through the wire, if anything at all, not just the fact that it has resistance. Also, extra loads attached to the wire increase the resistance of the circuit and can limit the current through that wire's resistance.
     
    Last edited: Feb 7, 2008
  5. Feb 7, 2008 #4
    current is like traffic flow of electron. low resistance of course more current. its like you driving a vehicle, if there is no traffic jam (low resistance), more cars will take that route.
     
  6. Feb 7, 2008 #5
    What then will cause a fuse to pop when the resistance in the circuit is increased?

    Hasn't the current flow somehow increased if the fuse has been popped?
     
  7. Feb 7, 2008 #6

    chroot

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    Fuses don't blow when resistance increases; they blow when resistance decreases (and current becomes unacceptably large).

    Do you have a specific scenario in mind? You seem to be misunderstanding it.

    - Warren
     
  8. Feb 7, 2008 #7
    I'm thinking of 12-volt automobile electrical system.

    Say a portion of exposed wire is corroded. The corrosion results in increased resistance in the circuit. If it's bad enough, the corroded section could get hot enough to potentially start a fire.

    Isn't this why fuses are installed in various circuits?
     
  9. Feb 7, 2008 #8
    No. The corroded section might start a fire because it now has resistance that results in power dissipation (I^2*R), but that would be unlikely. I once had a car where the starter cable (very high current) was so corroded that I would have to bang on it to get it to start. But it never got more than a little hot at 12V. If you had the same situation at a higher voltage (say 120 VAC), you often get enough heat to start a fire. In those cases, the fuse will not normally open.
     
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