It’s time to clean the carpets. I plug in the vacuum cleaner and switch on at the socket. Then I switch the machine on and start work. Considerable energy is needed creating and maintaining suction and beating the carpet at the same time. Whatever energy I need the machine to use, luckily comes straight down the cable at just the right time. If I turn on ‘boost’, the rate at which electrical power comes down the cable increases to match. Great job done. Now I turn the machine off and unplug it, and even if I were to try to turn it on, it won’t respond.