and

P=ExI

P = 2 volts x 1 ampere

P = 2 watts

When E is increased to 3 volts:

and

P=ExI

P = 3 volts x 1.5 amperes

P = 4.5 watts

You should notice that when the voltage was increased to 2 volts, the power

increased from .5 watts to 2 watts or 4 times. When the voltage increased

to 3 volts, the power increased to 4.5 watts or 9 times. This shows that if

the resistance in a circuit is held constant, the power varies directly with

the square of the voltage.

Another way of proving that power varies as the square of the voltage when

resistance is held constant is:

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