## Introduction: Calculating Power (Interactive!)

**Watch the video to learn more about how to calculate power in a circuit using a simple equation to work out the power consumed in Watts. Apply it to any device or circuit.**

**Try this Circuit!: **

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## 7 Comments

P=IV? P=IU!

I'm not sure what your question is here?

The video shows the formula P=IV. This is wrong. I is the symbol for current, and A (Ampere) is the unit. V (Volt) is the unit of voltage but the symbol for voltage is U. P is the symbol for power and its unit is W (Watt) or VA (Volt Ampere). So you either need to write P=UI or 1W = 1V*1A.

I understand that many europeans use U as the symbol for voltage. But most use the SI Unit; V. The aim of my videos is to keep it simple, and explaining the differences between symbols can cause confusion. Perhaps a separate video for this in the future. All-in-all, the calculation works the same whether you use a U or V to represent voltage. P=UI is the same as P=IV. I think it's unfair to state that it's wrong, It's just a matter of preference and how you were taught.

I was not aware of the SI system (probably like most US people are not aware of a metric system). But then this system states the symbol for current is A and for wattage its W (always the same as the unit: http://www.alcyone.com/max/reference/physics/units.html and https://en.wikipedia.org/wiki/International_System_of_Units). So if you reference the SI system you would need to specify W = VA.

Again, this is a matter of where you were taught and your preferences.

This is the SI Notation system I was taught: http://physics-help.info/physicsguide/appendices/si_units.shtml

If you prefer to use those symbols, I have no issues with that. But as I said, it's not really acceptable to state that either method is wrong given that there are many acceptable variations of notation.

Well, that now makes the confusion perfect. A system where you can choose amongst a variety of symbols to denote a physical size? The site you reference is simply wrong. You need to cite NIST in that place: http://physics.nist.gov/cuu/pdf/sp811.pdf and they use W for wattage.