Physics › Section O · Current and circuits › Topic O.6
Emf and terminal voltage
Turn the key in an old car with the headlights on and the lights dim as the starter motor turns. The battery has not changed; its output voltage has. Emf and internal resistance explain why a real source gives less voltage the more current you take from it.
In this topic
- What a source does
- Internal resistance
- Worked example: starting a car
- Current from a real source
- Worked example: a fresh and a tired cell
- Charging a battery
- Combining sources
- Measuring an emf
- Common mistakes to avoid
- Key takeaways
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