State ohm's law.if the applied voltage is increased does the resistance of a conductor change at constant temperature ?
Answers
Ohm’s law states that Voltage is directly proportional to the Current passing through the conductor. If you remove the sign of proportionality, then a constant will into the equation. According to Ohm’s law, this constant is the Resistance of the conductor.
But research shows that the Resistance is directly proportional to length of the conductor and inversely proportional to the area of cross-section of the conductor. Again, when we remove the sign of proportionality, a constant will be introduced into the equation. This constant is called the Resistivity of the material. The resistivity depends on the type of material and is supposed to be constant.
But it was later found that Resistivity of a material may change with respect to the temperature. It increases in case of conductors and decreases in case of semi-conductors. Hence Resistivity turned out to be a variable making the Resistance a variable too and hence proving Ohm’s Law wrong.
As the only parameter that made the Resistivity variable was temperature, hence temperature is taken as constant.
Constant temperature makes the resistivity constant which made resistance constant. Constant resistance again made the Ohm’s law applicable.
That’s why Ohm’s law is applied only at constant temperature. It is like the “conditions apply” of the law. If temperature is not constant then the very statement of the law becomes wrong.