How to Verify Ohm's Law

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Ohm's Law is a mathematical formula first proposed George Ohm. This law states that the current in a conductor is directly proportional to the voltage across it, and inversely proportional to its resistance. This means that current will increase in a circuit if the voltage is increased while resistance remains the same, but that current will decrease if resistance is increased while the voltage remains the same.

Things You'll Need

  • 1 1-Ohm ceramic resistor
  • 1 10-Ohm ceramic resistor
  • 1 spool red wire
  • 1 spool black wire
  • 12-volt lantern battery
  • Digital multimeter
  • Wrap the end of a red wire around one metal leg of a 1-Ohm resistor. Wrap the end of a black wire around the other end of the 1-Ohm resistor. Connect the red wire to the positive (+) terminal of a 12-volt battery and the black wire to the negative (-) terminal of the battery.

  • Turn on a digital multimeter and rotate the dial to the setting labeled "Volts DC" or "VDC." The dial selector should be pointed to "12 VDC." Touch the tip of the red test probe of the multimeter to the resistor leg to which the red wire is connected. Touch the tip of the black test probe at the same time to the resistor leg to which the black wire is connected. Write down the voltage in the circuit that appears on the readout of the multimeter. For example, you write down "12 volts."

  • Set the dial on the multimeter to measure 20 Amps of current by rotating the dial to the setting labeled "20 Amps". On some meters, you must unplug the red probe wire from the voltage jack and insert it into the "Amperage" jack on the meter. Touch the tip of the red test probe of the multimeter to the resistor leg to which the red wire is connected. Touch the tip of the black test probe at the same time to the resistor leg to which the black wire is connected. Write down the value for current that appears on the readout of the multimeter. For example, you write down "12 Amps."

  • Divide your voltage value by your current value. For example, if you measured 12 Volts and 12 Amps in the circuit, 12/12 = 1. You have proven that Ohms Law is verifiable because the resistor is 1 Ohm.

  • Verify Ohm's Law by using the multimeter to measure resistance in the circuit. Disconnect power to the circuit by removing the wires from the battery. Rotate the dial on the multimeter to the setting labeled "1 Ohm." If the meter you are using does not have a "1 Ohm" measurement setting, set the dial to the next higher Ohm measurement value on the dial. Touch the red probe tip to one leg of the resistor and the black probe tip to the other leg of the resistor. The value displayed on the meter will be 1.000.

Tips & Warnings

  • Never measure resistance with a digital multimeter when power is flowing through the circuit. The resistive division network circuitry in a multimeter can be damaged if current flows across it while the meter is set to measure resistance.

References

  • Photo Credit Comstock/Comstock/Getty Images
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