CoachThe power of a device is the rate at which it converts energy — joules per second. Its unit is the watt (): one joule each second, honoring the engineer of the steam age; the kilowatt ( ) serves the kitchen’s heavyweights. Power is not an amount of energy but a pace of spending — a tap’s flow, not a bucket’s content.
Examples
Example 68.3 (The household ladder)
Read the plates on the family’s machines: an indicator light, ; a modern lamp, (its glowing ancestor spent sixty for the same light — the difference was heat); a laptop, ; a television, ; a washing machine heating its water, ; the kettle, ; an instant water heater, up to . The pattern of the ladder: anything whose job is heating climbs to the kilowatts — warmth is the costliest form of energy to supply.
Example 68.8 (Reading the bill)
The meter by the front door counts every kilowatt-hour that enters the house; the bill is its month’s difference times the tariff. A typical family’s monthly units decompose by audit: water heating and radiators first (the kilowatt club), then the cold appliances — modest watts, but running always — then cooking, washing, light and electronics. The audit’s power: it finds the real levers. Replacing ten old bulbs with ones saves more than unplugging every charger in the house a thousand times over.
Example 68.9 (The standby vampires)
Small print, long hours: a television’s standby light sips — but for all hours of the month: . One vampire is harmless; a house with twenty sippers at a watt each pays monthly for nothing. Power times time forgives no term: the second factor bites when the first one hides.