Alternating current

An alternating current (AC) was a type of electric current.

By the 1900s, use of AC was proposed by Nikola Tesla. His ideas were opposed by the public. Protesters called it "death current". Thomas Edison called it "the most deadly force known to science". (TV: Nikola Tesla's Night of Terror)

AC supply's voltage could be changed by transformers. (TV: Revenge of the Slitheen)