Study Notes
The topic covers the concepts of electromotive force (EMF) and internal resistance in electrical circuits, focusing on how energy is transferred and lost within a circuit. It also explores how resistance varies in different components like filament lamps and sensors such as LDRs and thermistors.
- Electromotive Force (EMF) — The amount of chemical energy converted into electrical energy per coulomb of charge. Example: A battery converting stored chemical energy into electrical energy.
- Internal Resistance — The resistance within a power supply that causes energy dissipation as heat. Example: A battery warming up as current flows through it.
- Terminal Potential Difference — The voltage available across the terminals of a cell or battery. Example: The voltage measured across a battery when connected to a circuit.
- Light-Dependent Resistor (LDR) — A resistor whose resistance decreases as light intensity increases. Example: An LDR used in streetlights to turn them on at night.
- Thermistor — A resistor whose resistance decreases as temperature increases. Example: A thermistor used in a digital thermometer to measure temperature changes.
Exam Tips
Key Definitions to Remember
- Electromotive Force (EMF)
- Internal Resistance
- Terminal Potential Difference
- Light-Dependent Resistor (LDR)
- Thermistor
Common Confusions
- Confusing EMF with terminal potential difference
- Misunderstanding the effect of internal resistance on voltage
Typical Exam Questions
- What is the difference between EMF and terminal potential difference? EMF is the total energy per charge from the power supply, while terminal potential difference is the voltage across the load.
- How does internal resistance affect the performance of a battery? It causes energy loss as heat, reducing the terminal potential difference.
- How does the resistance of a filament lamp change with temperature? The resistance increases as the temperature rises, causing the current to increase more slowly.
What Examiners Usually Test
- Understanding of how EMF and internal resistance affect circuit performance
- Ability to calculate resistance using Ohm's law and graphical methods
- Knowledge of how resistance changes in different components like LDRs and thermistors