Megajoules are one unit of measure for electric power.
 The joule was explicitly intended as the unit of energy to be used in both electromagnetic and mechanical contexts
 Wilhelm Siemens, in his inauguration speech as chairman of the British Association for the Advancement of Science (23 August 1882) first proposed the Joule as unit of heat, to be derived from the electromagnetic units Ampere and Ohm, in cgs units equivalent to 107 erg

