Resistance

Resistance is a fundamental concept in physics that describes how a material opposes the flow of electric current. In the WJEC A-Level Physics specification, resistance is studied as part of the 'Electric Circuits' topic, which builds on GCSE knowledge and introduces more advanced analysis. Understanding resistance is crucial for predicting current and voltage in circuits, designing electronic devices, and explaining energy transfer in resistors. This topic also lays the groundwork for later study of electromagnetism and alternating current.

The key equation for resistance is Ohm's law: V = IR, where V is voltage (in volts), I is current (in amperes), and R is resistance (in ohms). However, not all components obey Ohm's law; those that do are called ohmic conductors (e.g., fixed resistors at constant temperature). Non-ohmic components, such as filament lamps and diodes, have a resistance that changes with voltage or current. The WJEC syllabus requires students to investigate the I-V characteristics of these components and understand the factors affecting resistance, including length, cross-sectional area, temperature, and material resistivity.

Resistance is also linked to electrical power: P = IV = I²R = V²/R. This is essential for calculating energy dissipation in resistors and understanding why components heat up. In practical circuits, resistors are used to control current, divide voltage, and protect sensitive components. Mastery of resistance calculations and circuit analysis is vital for exam success and for further study in engineering or physics.