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⚡ Power and Watts

Discover what power really means in physics — how fast energy is transferred — and learn to measure it in watts using P = energy ÷ time.

lessons

~15 min

to learn

🔬 Science

subject

Teens

level

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What you’ll learn

What Power MeansUnderstand that power is the rate of energy transfer, not the total energy used.Power measures how quickly energy is transferred, not how much. Doing the same job in less time takes more power. Two builders can transfer equal energy, yet the faster one is more powerful.
Measuring Power in WattsDefine the watt as one joule per second and calculate power from energy and time.Power is measured in watts, where one watt is one joule per second. To find power, divide energy transferred by time taken. Device labels show power ratings so we can compare how fast they use energy.
Power in Everyday LifeCompare the power ratings of everyday devices and link high power to fast energy transfer.Everyday devices have very different power ratings, from a 5 W charger to a 2500 W kettle. High-power devices transfer lots of energy each second, often as heat, and so use more energy overall.

Questions this course answers

What does power measure?

Power is the rate of energy transfer — how much energy is moved each second.

Two builders each transfer 3000 J of energy, but one takes 10 s and the other 60 s. Who is more powerful?

Same energy in less time means more power. The 10 s builder transferred the energy far faster.

What does one watt mean?

A watt is a joule per second: 1 W = 1 J/s. It links the unit of power to the unit of energy.

A motor transfers 2000 J of energy in 4 seconds. What is its power?

Power = energy ÷ time = 2000 ÷ 4 = 500 W.

How many watts are in 1 kilowatt?

1 kilowatt (kW) = 1000 watts, just as 1 kilometre is 1000 metres.

Which device has the highest power rating?

The kettle at 2500 W transfers energy fastest, which is why it can boil water so quickly.

Grounded in trusted sources

BBC Bitesize — Energy
The Physics Classroom
Britannica

Every Wunder lesson is built from real, reputable sources — never invented.

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