Constructing experiment to prove P=IV

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PhysicsLearne
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Not sure if the title is clear enough, but basically I've got a practical in a couple of days time and I have to construct an experiment to prove that P=IV by proving that P is greatest when the value of r (internal resistance) is zero and total resistance is equal to R (normal resistance).

I'm quite confused at what this is actually asking me to to do. Any ideas.

thanks
 

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Is this a real project or a virtual project? One accurate way to measure power is to heat a resistor in a calorimeter, and measure the energy transferred to a cup of water. Suppose you had a 12-volt car battery with an internal resistance with about r = 1/100 ohm. Get a R=1 ohm resistor and put it in about a cup (about 225 cc) of water, and connect it to the battery. Get a thermometer and measure the rate at which the water heats up. P = I*V = V^2/R = 144 watts. Only about 1% of the battery power is lost in the internal resistance r.
 
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