Transformers

Two coupled coils that step AC voltage up or down; they also provide electrical isolation.

Easy

For an ideal transformer with $N_p$ primary and $N_s$ secondary turns:

$\frac{V_s}{V_p} = \frac{N_s}{N_p} = \frac{I_p}{I_s}$

Power in ≈ power out, so stepping voltage down steps current up. Transformers work only with changing current — DC passes no energy across.

An impedance on the secondary appears on the primary multiplied by $(N_p/N_s)^2$ , which is used for impedance matching in audio and RF. See Electrical → Electrical Machines → Transformers for losses, efficiency and construction.

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