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T³: Adventures in Science – Electric Power

Power is the rate of doing work, and for electricity, that means the rate in which energy is converted in a circuit.

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Power is the rate in which work is done, much like kilometers (or miles) per hour is a rate. The SI unit for power is the Watt, and it's defined as one joule per second. Whether it takes you three seconds or one second to move 100kg to 1m above the ground, you use the same amount of energy. However, it requires more power to do it in one second.

When it comes to electric power, "work done" refers to the ability of the circuit to transform electrical energy into something else, like heat, motion or sound. "Work done" can also refer to transforming some other form of energy into electrical energy, as in a battery, which converts chemical energy to electrical energy.

As power is work done per unit time, with a little bit of math we find that electric power is defined as voltage times current:

Electric power equation

The ability to convert electric power is quite helpful, as it allows us to do things like light up the filaments in light bulbs, spin motors and drive speakers. In the video, we show examples of some of these and talk about why things like resistors heat up when current moves through them.

The written tutorial for electric power can be found here:

Electric Power

June 26, 2013

An overview of electric power, the rate of energy transfer. We'll talk definition of power, watts, equations, and power ratings. 1.21 gigawatts of tutorial fun!

Once again, feedback is welcome and appreciated!

Interested in learning more foundational topics?

See our Engineering Essentials page for a full list of cornerstone topics surrounding electrical engineering.

Take me there!

Comments 7 comments

  • "Older" electric stoves? Maybe conventional (or resistive) electric stoves (ranges). I hope it isn't me being an old fogey, but I don't think the adjective "older" is appropriate.

    Those coiled resistive heating elements are still current art. Yes, there are glass-top electric ranges (the coiled resistive heating element is under the glass), and induction ranges. But induction ranges aren't replacing resistive electric stoves, in part due to the restricted cooking vessel material. And it only takes one broken glass top to steer someone back to the exposed coils...

    Looking at Home Depot's website in Electric Ranges, there are 299 models. If I filter by coil cooking surface there are 93 results. If I filter by induction cooking surface there are 14 results.

  • Good overview for only being about 5 minutes! You did mention (in passing) the horsepower. I was hoping that maybe in the text tutorial it might be mentioned that the horsepower is (about) 746 watts. (An easy memory aid for this bizarre number [though not likely historically accurate] is "In 1492, Columbus sailed the ocean blue, with horses, of which he had two" -- note that 2 horsepower is [about] 1492 watts.)

    Off on a related tangent, I've noticed that here in the U.S. we tend to rate engines in horsepower, but in Europe they rate them in kW.

    • Well they are rated in kW, but pretty much everybody still talks about them using horsepower. I don't think I've ever heard anybody brag about how many kW his car has XD

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