Electrical Systems

Electrical systems (AS91526) is a 6-credit external in four connected parts:

• Resistors in DC circuits — real batteries with internal resistance, and Kirchhoff's two bookkeeping laws.
• Capacitors — storing charge and energy, and the exponential story of charging through a resistor.
• Inductors and induction — magnetic flux, Faraday's and Lenz's laws, self-inductance, and the transformer.
• AC circuits — rms values, reactance, phasors, impedance, and resonance in LCR circuits.

The through-line: capacitors and inductors are mirror images. A capacitor resists changes in voltage, an inductor resists changes in current; each stores energy (in an electric or magnetic field), each has a time constant ($\tau = RC$ or $\tau = L/R$), and in AC each has a reactance that depends on frequency in the opposite way. Every relationship is on the exam resource sheet — the marks are for choosing well and explaining the physics.