Induction and power transmission
A changing magnetic flux induces a voltage, which is how generators and transformers work and why grids use alternating current.
A worked example
A transformer with 200 turns on the primary and 20 on the secondary steps 4 000 V down to 400 V, a ratio of ten to one.
The mistake people actually make
A steady magnetic field induces nothing; only a change in flux does. Transmission at high voltage cuts the current, and line loss goes as current squared, so halving the current quarters the loss.