• summary_type: concept
• word_count: 170

A transformer transfers AC power between circuits via mutual induction. Ideal transformer: V_s/V_p = N_s/N_p (turns ratio), I_sV_s = I_pV_p (power conservation), so I_s/I_p = N_p/N_s. Step-up (N_s > N_p) increases voltage and proportionally decreases current. Step-down does the opposite. Impedance transformation: Z_s = (N_s/N_p)^2 * Z_p — used for impedance matching in audio and RF circuits. Real transformer losses: (1) Copper losses (I^2R in windings) — minimized by thick, low-resistance wire. (2) Eddy current losses (induced currents in core) — minimized by laminated core (thin insulated sheets). (3) Hysteresis losses — minimized by soft iron core (narrow hysteresis loop). (4) Flux leakage — minimized by winding coils over each other. Efficiency = output power/input power x 100%, typically 90-99%. Transformers only work with AC — DC produces constant flux and zero induced EMF. Long-distance power transmission uses step-up to reduce current and minimize I^2R line losses.