4.Main Content
experiments
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
Safety
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
1 You can calculate the value of the resistance from the root mean square (rms) readings of current and voltage.
2 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-checked in October 2006