Transformers
Year 11 (IGCSE) ⚡ Electricity & Magnetism Apply the transformer equation V₁/V₂ = N₁/N₂; explain step-up/step-down.
⚡ How Transformers Work
A transformer changes AC voltage using electromagnetic induction. It has two coils (primary and secondary) wound on an iron core.
Transformers only work with AC (alternating current) — not DC!
📐 Transformer Equation
The ratio of voltages equals the ratio of turns.
Transformer Equation
$$\frac{V_1}{V_2} = \frac{N_1}{N_2}$$
$V_1$ = primary voltage · $V_2$ = secondary voltage · $N_1, N_2$ = number of turns
Step-up transformer: N₂ > N₁ → V₂ > V₁ (e.g. power grid, 11 kV → 400 kV)
Step-down transformer: N₂ < N₁ → V₂ < V₁ (e.g. 230 V mains → 12 V for a laptop)
Step-down transformer: N₂ < N₁ → V₂ < V₁ (e.g. 230 V mains → 12 V for a laptop)
⚡ Power & Efficiency in Transformers
For an ideal transformer, power in = power out.
Power Conservation
$$V_1 I_1 = V_2 I_2 \quad \text{(ideal transformer)}$$ Why transmit at high voltage? High V → low I → less power wasted as heat in cables (P = I²R).
Ready to test yourself? Click the Quiz tab above to answer questions on this topic!
⚡ Transformer Calculator
Power & Current in Ideal Transformer