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Power is a rate; electricity use is an amount

Appliance labels and electricity bills use kilowatts (kW) and kilowatt-hours (kWh) for different quantities. A kilowatt measures power, the rate of energy use, while a kilowatt-hour measures an amount of energy. Compare a speedometer with an odometer to explore why a rate and an accumulated total answer different questions.

2–3 min

Questions you could explore

  • What extra information turns a power rating into an energy estimate?
  • How could two appliances with the same power rating use different amounts of energy in a day?

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How can a heat pump deliver more heat than its electricity input?

Energy4–5 minA heating device seems to promise something impossible when its heat output exceeds the electricity it uses. A heat pump's energy account includes another input: heat moved from its surroundings.

Energy

A solar cell's route from light to electricity

Shining sunlight onto a piece of silicon is only the first step in making solar power. When incoming photons knock electrons loose inside the semiconductor, an internal electric field built into the solar cell's layers must separate those charges and guide them into an external circuit before they simply recombine.

4–5 min

A solar cell's route from light to electricity

Energy4–5 minShining sunlight onto a piece of silicon is only the first step in making solar power. When incoming photons knock electrons loose inside the semiconductor, an internal electric field built into the solar cell's layers must separate those charges and guide them into an external circuit before they simply recombine.

How does a wind turbine turn moving air into electricity?

Energy3–5 minA turbine's blades are only the visible beginning of the journey from wind to electricity. Their rotation drives a generator, though the machinery connecting those parts differs between turbine designs.

Power is a rate; electricity use is an amount | Speech Topic | speaking.app