Question

Using scientific principles, explain in detail how ambient temperature affects resistance and what are its consequences on power ratings of a carbon resistor in a circuit?

Answer 1

Electric current is nothing but flow of FREE electrons around in the conductor. know that the resistance is given by R=pl/A.

Where R is resistance and p is resistivity of the conductor. l and A are length and cross sectional area of the conductor. As you can see above resistance is directly proportional to the resistivity.

But the resistivity is directly proportional to the temperature. its relation is given as

p=po(1+(T-To)).

Where To is reference temperature and po is resistivity at that reference temperature. is the temperature coefficient.

So from above two,we can say that the resistance of a conductor is directly proportional to the temperature. As temperature increases, the resistance of a conductor also increases.

Now coming to the concept, when you increase the temperature, you are giving more energy to the electrons. So due to this extra energy, electrons vibrate. As electrons vibrate it generates more heat in the wire in which electric current is flowing. So it becomes difficult for the electrons to move around freely among them. As they're UNABLE to move FREELY the conductor, we say that the resistance of the conductor is increased.

As resistance increases the power dissipation in the circuit increases so the overall power rating goes down for that particular conductor.

Hope this helps.

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