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Old 10-02-2007
ryan_975 ryan_975 is offline
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Originally Posted by jonnyGURU View Post
Well, yeah. That's kind of my point. How would you actually know the wattage and not either the voltage or current (of course, if you knew either and the wattage than you can figure out the other.)

I just think some people make explaining electrical theory overly complicated just for the sake of it.

Well, say you have a circuit that has to stay under 500 watts (because you're using a shared 110v/15a branch circuit), and you have to need to maintain a constant current of 5 amps (for say a lead acid battery charger). You need to find out what the resistance needs to be so you can choose your components. You'd have to use P=IČR to solve the problem.

500 = 5ČR;
500 = 25R;
500/25 = 25R/25;
20 = R.

Your circuit can have a resistance of no more than 20 Ohms.
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