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Question
The thermal energy developed in a current-carrying resistor is given by U = i2 Rt and also by U = Vit. Should we say that U is proportional to i2 or i?
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Solution
In the expression U = Vit, voltage V and current i are variables for a given time interval. So, based on this expression we cannot say that U is proportional to i. In the expression U = i2Rt, the resistance R is fixed for a circuit for a given time interval. So, based on this expression, we can say that U is proportional to i2 and not i.
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