Study Notes
Resistance is the opposition to the flow of electric current in a material, measured in ohms. Resistivity is a material property that quantifies how strongly a substance opposes the flow of electric current, measured in ohm meters.
- Resistance — the opposition encountered by electric current in a material. Example: Copper has low resistance, making it a good conductor.
- Ohm's Law — states that current is directly proportional to voltage at constant temperature. Example: V = IR, where V is voltage, I is current, and R is resistance.
- Ohmic Conductors — materials that follow Ohm's Law with a linear I-V relationship. Example: Metallic conductors like resistors.
- Non-Ohmic Conductors — materials that do not follow Ohm's Law. Example: Filament lamps and diodes.
- Resistivity — a measure of how strongly a material opposes current flow. Example: Copper has low resistivity, while insulators have high resistivity.
- Light-Dependent Resistor (LDR) — a resistor whose resistance decreases with increasing light intensity. Example: Used in streetlights to turn on automatically in low light.
- Thermistor — a resistor whose resistance decreases with increasing temperature. Example: Used in digital thermometers to measure temperature changes.
Exam Tips
Key Definitions to Remember
- Resistance: Opposition to electric current.
- Ohm's Law: V = IR.
- Resistivity: Material property opposing current.
- Ohmic Conductors: Follow Ohm's Law.
- Non-Ohmic Conductors: Do not follow Ohm's Law.
Common Confusions
- Confusing resistance with resistivity.
- Assuming all materials follow Ohm's Law.
Typical Exam Questions
- What is Ohm's Law? Ohm's Law states that current is directly proportional to voltage at constant temperature.
- How does resistance change with temperature in a filament lamp? Resistance increases with temperature, causing current to rise more slowly.
- What factors affect the resistance of a wire? Length, cross-sectional area, and resistivity.
What Examiners Usually Test
- Understanding of Ohm's Law and its application.
- Ability to distinguish between ohmic and non-ohmic conductors.
- Calculating resistance using V = IR and interpreting I-V graphs.