Current, voltage and resistance are the three fundamental quantities that describe how electricity behaves in a circuit, and their relationship, defined by Ohm's law, is one of the most important formulas in IGCSE Physics.
1. Defining Current, Voltage and Resistance
Current is the flow of electric charge measured in amperes, voltage is the energy transferred per unit charge measured in volts, and resistance is the opposition to current flow measured in ohms. Each plays a distinct role in determining circuit behaviour.
2. Ohm's Law
Ohm's law states that voltage equals current multiplied by resistance, expressed as V = IR, provided temperature remains constant. This formula allows students to calculate any one of the three quantities if the other two are known.
3. Factors Affecting Resistance
Resistance in a wire depends on its length, cross-sectional area, material and temperature. Longer and thinner wires have greater resistance, while most materials increase in resistance as temperature rises.
4. IV Characteristic Graphs
An IV characteristic graph plots current against voltage for a component. A straight line through the origin indicates constant resistance, such as in a resistor at constant temperature, while a curve indicates changing resistance, as seen in a filament lamp that heats up.
Frequently Asked Questions
What is Ohm's law?
Ohm's law states that voltage equals current multiplied by resistance (V = IR), provided the temperature of the conductor stays constant.
What happens to resistance when a wire gets longer?
Resistance increases as a wire gets longer, since the electrons must travel further and encounter more collisions with the wire's particles.
Conclusion
A strong understanding of Ohm's law and the factors affecting resistance is essential for solving both theoretical and numerical questions across the electricity section of the IGCSE syllabus.