Edexcel A Level Physics:復習筆記3.16 Internal Resistance
Internal Resistance
- All power supplies have some resistance between their terminals
- This is called?internal resistance?(r)
- Internal resistance causes some electrical energy to be transformed to heat energy in the power supply itself
- This is why the cell becomes warm after a period of time
- Therefore, the internal resistance causes?energy loss in a power supply
- A cell can be thought of as a source of e.m.f. with an internal resistance connected in series
- The amount of voltage lost is known as the 'lost volts'
- A higher internal resistance will result in a higher value for lost volts
Circuit showing the e.m.f and internal resistance of a power supply
- Where:
- R?= resistance of the circuit (the ‘load resistor’)
- r?= internal resistance
- ε?= e.m.f.
- Vr?= 'lost volts'
- VR?= voltage across the load (sometimes also called?VT, the terminal voltage)
Exam Tip
The internal resistance concept catches many students out. Make sure you fully understand the circuit diagram;
- Internal resistance of the cell can be treated as though it were a separate resistor - although it isn't!
- The load? resistance is treated as another resistor in series
- Potential difference is measured across the load resistor
- The lost volts are calculated as though they were the potential difference across the 'internal resistor'
轉載自savemyexams
翰林AMC8視頻課重磅上線！
國際競賽真題資源免費領取
