Summary and Exam Tips for Resistance and Resistivity
Resistance and resistivity is a subtopic of Electricity, which falls under the subject Physics in the Cambridge International A Levels curriculum.
Resistance is the opposition to the flow of electric current in a material, measured in ohms (Ω). Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, expressed as . Resistance can be determined using a circuit with a voltmeter and ammeter, or graphically by plotting voltage against current. Ohmic conductors follow Ohm's Law, while non-ohmic conductors like filament lamps have resistance that changes with temperature. I-V characteristics graphs illustrate these relationships, with metallic conductors showing linear graphs and semiconductor diodes allowing current flow in one direction. Resistivity () is a material property affecting resistance, influenced by wire length, cross-sectional area, and the material itself. Sensors like LDRs and thermistors are non-ohmic conductors, with resistance varying with light and temperature, respectively. LDRs are used in light-sensitive applications, while thermistors are used in temperature sensing.
Exam Tips
- Understand Ohm's Law: Be able to apply to solve problems involving voltage, current, and resistance.
- Graph Interpretation: Practice interpreting I-V graphs for different conductors, noting linearity for ohmic conductors and non-linearity for non-ohmic ones.
- Material Properties: Remember that resistivity depends on material, length, and cross-sectional area. Know examples like copper for low resistivity.
- Sensor Applications: Familiarize yourself with how LDRs and thermistors work and their practical applications in circuits.
- Temperature Effects: Understand how temperature affects resistance, especially in filament lamps and thermistors.
