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Find Amp of Circuit

  1. May 29, 2012 #1
    I'm trying to find the amp of a circuit. Okay I know a circuit has a resistivity, So for example if my circuit is made out of cooper which has a resistivity of 1.68 * 10 negative power of 8 and a voltage of 9 volts.So do I just use ohms law Volt / Resistant = Amp?
  2. jcsd
  3. May 29, 2012 #2


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    Gold Member

    Yes, use Ohm's Law. Current equals Voltage divided by resistance. For a great explanation and built-in calculator, see:


    By the way, it's important to get your terminology and units correct

    Current (I): units of Amperes
    Voltage (E): units of Volts
    Resistance (R): units of Ohms
  4. May 29, 2012 #3


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    Staff: Mentor

    Be sure to carry units along in your calculations -- it's important to have the units of the resistivity in order to get the correct answer for the resistance.

    In this case, you would need to be sure to include the source resistance of your "9V" source. When you put a heavy load on a voltage source, its internal resistance needs to be part of your calculation (using Ohm's Law, yes).
  5. May 29, 2012 #4


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    Science Advisor

    But first you will need to convert from resistivity to resistance.

    For this, you need the formula:

    R = resistance of the metal sample.
    ρ is the resistivity (in ohm -meters).
    L is the length of the sample in the direction of current flow (in meters).
    A is the cross sectional area of the sample (in square meters).
    Last edited: May 29, 2012
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