Which statement best describes the role of the transformer inside a typical mobile phone charger plugged into a household 230V wall socket?
a) It is a step-up transformer that raises the 230V mains to an even higher voltage so that the phone charges faster.
b) It merely converts the alternating supply into direct current without altering the voltage level.
c) It is a step-down transformer that lowers the voltage and increases the current to a safer level.
d) It is an isolation transformer that keeps the voltage about 230V but separates the phone from the mains for safety.