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How to Calculate Volts & Amps With Coiled Wire

Calculating Ohm's Law for volts and amps in direct current circuits is normally straightforward -- simply use variations of the relation, V = I * R, where "V" is voltage, "I" is current in amps and "R" is resistance in ohms. However, in a coil of wire, Ohm's Law becomes a little more complicated. Magnetism between adjacent turns of wire produces a phenomenon called the proximity effect, restricting the flow of current and raising the coil's electrical resistance by about 100 percent. To find resistance, "R," for a straight wire, you multiply the resistivity value for the wire by the length; for a coil, you double the result.

Things You'll Need

Calculator

Instructions

- 1
  Determine the wire's resistivity in terms of ohms per meter, and then enter this figure into your calculator.
- 2
  Press the multiply key, and then enter the wire length in meters. Note that this is not the length of the coil but the entire length of wire if it were straightened out. Press the multiply key, enter the number "2," and then press the multiply key again to have the calculator display the resistance of the wire coil in ohms.
- 3
  Enter the current passing through the coil in amps, and then press the multiply key. The result is the voltage across the coil in volts. For example, if a coil has a resistance of 10 ohms and it carries 2 amps of current, multiply 10 by 2 to get the voltage value of 20 volts.

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