Today I saw the professor demonstrate a complete breakdown in ohm's Law. How does a designer select resistors for a circuit if ohms law does not hold up over varying tempuratures? E.G. say you are trying to drive a light bulb that requires 0.25 A at some voltage.

Question

Today I saw the professor demonstrate a complete breakdown in ohm's Law.  How does a designer select resistors for a circuit if ohms law does not hold up over varying tempuratures?  E.G. say you are trying to drive a light bulb that requires 0.25 A at some voltage.

anonymous · Answer

well one of the most refractory metals is Tungsten it has viral applications in scientific research and in many high tech devices. 
In room temprature temperature coefficient is 
$$a=4,1*10^-3 K^-1$$$$Rr=Ro(1+a*θ)$$θ=temprature in K
Ro=Ressistivity in 273K
Also under normal conditions it is stainless.
But even that metal got a weak point,its resistivity in high tempratures (273K-2500K) resitivity changes 15 times!

anonymous · Answer

choose a resistance with very low temperature coefficient such that the change in temperature effect the resistor negligibly.

NOTE: the ohm's law is valid for all the cases. In ohmic conductor resistance is constant so graph is linear but in non-ohmic conductor the resistance is not constanat so graph is not-linear.

anonymous · Answer

Thank you both.

theraggedydoctor · Answer

You're welcome.