What is the effect of temperature on ohms law?

Answer

One of the conditions for Ohm's Law to apply is that the temperature of a conductor MUST remain constant. And, unfortunately, this is difficult to achieve because as the applied voltage increases, the resulting current causes the temperature of the conductor to rise -thus negating Ohm's Law!!

For Ohm's Law to apply, the ratio of voltage to current must remain constant for variations in voltage. If it doesn't, then the conductor/device is NOT obeying Ohm's Law. Period! So if, for example, you increase the voltage across a lamp, you will find that the ratio varies as the voltage increases, and this is because the resistance is increasing due to an increase in temperature. So, in this example, the temperature is the reason why lamps don't obey Ohm's Law.