Before deriving joules law you told generally that heat is directly proportional to resistance,time and current which means
H directly proportional to R I t
H=I R t right how you got I^2Rt
Kindly explain me

Generally, the heat produced in a resistor is directly proportional to the resistance.

$H\propto R$

And, heat produced is also directly proportional to the time.

$H\propto t$

Here we need to understand that the heat produced is directly proportional to the square of the current flowing through the resistor. The heat produced is not directly proportional to the current flowing.

So, $H\propto I$

Therefore, $H\propto I^2RT$

Or $H=kI^2RT$

If $H=1\ J$, $I=1\ A$, $R=1\ ohm$ and $t=1\ s$, then $k=1$

Then, $H=I^2RT$

Therefore we write the expression as $H=I^2RT$.

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Updated on: 10-Oct-2022

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