Transformer

A transformer is two coils (primary, secondary) magnetically coupled — usually via a laminated iron core to maximise flux linkage.

Ideal-transformer relation: V_s/V_p = N_s/N_p (turns ratio).

If N_s > N_p: step-up transformer (V_s > V_p but I_s < I_p). If N_s < N_p: step-down.

For an ideal (lossless) transformer: V_p·I_p = V_s·I_s (power conservation).

Transformers ONLY work with AC — they need a changing Φ. DC produces no induction.

Real transformers have losses: copper (I²R in windings), iron (eddy + hysteresis in core), flux leakage. Efficiency typically 95-99%.

Power transmission grid uses high-voltage AC (220-765 kV) precisely so transformers can step it up at the source and step it down at the consumer end — minimising I²R losses in transmission lines.