1) When a current passes through a copper wire in a magnetic field, it induces a voltage in the wire due to electromagnetic induction. 2) An alternating current generator uses a rotating coil in a magnetic field to generate a current, where the direction of the current reverses as the coil rotates. 3) Transformers use the principle of electromagnetic induction to change the voltage of an alternating current - a step-up transformer increases voltage through more turns on the secondary coil, while a step-down transformer decreases voltage.