Electricity and Magnetism covers circuit theory, Ohm\'s law, series/parallel networks, electrical power, static charge, magnetic fields, the motor effect, electromagnetic induction, and transformers.
Current I = Q/t (charge per second, amps). Potential difference V = W/Q (energy per coulomb, volts). Resistance R = V/I (ohms). Ohm\'s law: V = IR (for ohmic conductors). Series: same current, voltages add, R_total = R₁ + R₂. Parallel: same voltage, currents add, 1/R_total = 1/R₁ + 1/R₂. Power: P = IV = I²R = V²/R. Energy: E = Pt = IVt. Components: resistor, LDR (light → resistance ↓), thermistor (temperature ↑ → resistance ↓), diode (current one way), LED.
Magnetic fields: North to South. Plot with compass or iron filings. Earth has a magnetic field. Electromagnets: coil of wire + current; strength increases with current, turns, iron core. Motor effect: current-carrying wire in magnetic field experiences force (F = BIl). Fleming\'s left-hand rule: thuMb = Motion, First finger = Field, seCond = Current. DC motor: split-ring commutator reverses current each half-turn. Electromagnetic induction: changing magnetic field induces voltage (Faraday\'s law). Generator: rotating coil → AC voltage. Transformer: V₁/V₂ = N₁/N₂. Step-up: more secondary turns. Step-down: fewer. P₁ = P₂ for ideal transformer.
A transformer has two coils (primary and secondary) wrapped around the same iron core. When alternating current flows through the primary coil, it creates a changing magnetic field in the iron core. This changing field passes through the secondary coil and induces a voltage (electromagnetic induction). It only works with AC because induction requires a CHANGING magnetic field. DC produces a constant field — so once it\'s established, there\'s no change and no voltage is induced in the secondary coil. The voltage ratio equals the turns ratio: V₁/V₂ = N₁/N₂. For an ideal transformer, power is conserved: V₁I₁ = V₂I₂.
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