Ohm's law with alternating current

Demonstration

An ohmic resistor is equally ohmic when used with alternating current.

Apparatus and Materials

• Power supply, AC, low voltage variable
• Rheostat (10 - 15 ohms)
• Ammeter, (0-1 A), AC
• Voltmeter, 0 to 15 V, AC
• Leads, 4 mm, 6

Health & Safety and Technical Notes

Read our standard health & safety guidance

Procedure

1. Set up a simple series circuit using the AC terminals of the low-voltage supply in series with the ammeter and the rheostat, used here as a fixed resistor.
2. Connect the voltmeter in parallel with the resistor. Adjust the voltage so that a current of about 1 A flows.
3. Record a series of values of the current and potential difference as you gradually reduce the voltage applied.

Teaching Notes

• You can calculate the value of the resistance from the root mean square (rms) readings of current and voltage.
• The resistance will be the same value as in an experiment carried out with the same resistor using a DC supply.

This experiment was safety-tested in October 2006