A transformer transfers energy between two circuits through electromagnetic induction, they consists of two coils wound round a common iron core: the input coil is called the primary coil, the output coil is called the secondary coil
Transformers work since the alternating current in the primary coil induces an alternating magnetic field in the core, which in turn induces an alternating current in the secondary coil
The ratio of voltages in the coils is directly proportional to the number turns in the coils: VpVs = NpNs
The energy loss is virtually zero, so: VpIp = VsIs
High-voltage transmission
Transformers are used to boost the voltage in high-energy transmission, stepping up the voltage before transmission and stepping down at the end
High-voltage transmission minimises power loss: since power loss is directly proportional to the square of the current, to transmit a certain power, it is more advantageous to have a high-voltage & low current rather than vice versa