Summary
Practical circuits involve understanding how electrical components like batteries and resistors work together in a circuit. Key concepts include electromotive force (EMF) and internal resistance.
- Electromotive Force (EMF) — the amount of chemical energy converted into electrical energy per coulomb of charge. Example: A battery with an EMF of 12V converts 12 joules of energy per coulomb.
- Internal Resistance — the resistance within a power supply that causes energy dissipation as heat. Example: A battery with 1 ohm of internal resistance loses some voltage as heat.
- Lost Volts — the potential difference across the internal resistance of a power supply. Example: If a battery has an internal resistance of 1 ohm and a current of 2A, the lost volts are 2V.
Exam Tips
Key Definitions to Remember
- Electromotive Force (EMF)
- Internal Resistance
- Lost Volts
Common Confusions
- Confusing EMF with potential difference
- Misunderstanding the role of internal resistance in voltage drop
Typical Exam Questions
- What is the difference between EMF and potential difference? EMF is the energy supplied per coulomb of charge, while potential difference is the energy lost per coulomb.
- How do you calculate the terminal potential difference? Terminal p.d. is calculated as the EMF minus the lost volts.
- What happens to the terminal p.d. as current increases? The terminal p.d. decreases as current increases due to increased lost volts.
What Examiners Usually Test
- Understanding of how internal resistance affects circuit performance
- Ability to calculate EMF and terminal potential difference
- Differences between EMF and potential difference