5.1 Voltage, Resistance, and Current
5.2 Ohm's Law Formula
1. This week is on the internal resistance of a source such as a battery. Let's say that you were to put a voltmeter across a battery in an open circuit and it were to read 12 volts, the "no-load" voltage. Then lets say you close the circuit and the voltmeter drops to 11 volts. This suggests that your battery has an internal resistance that is zapping some of the force.
2. To measure the internal resistance (Ri) of a source:
- Measure the no-load voltage.
- Energize the circuit and then measure the voltage across the source again.
- Subtract the difference (internal resistance decreases the voltage in the circuit).
- Measure the current in the circuit.
- Use R=E/I to determine the internal resistance of the source.