Temperature variation of resistance?

Question

At 20 C, the carbon resistor in an electric circuit connected to a 5 V battery has a resistance of 200 Ohms. What is the current in the circuit when the temperature of the carbon rises to 80 C?

Answer 1

The resistance of the resistor increases linearly with temperature at these temperatures; the temperature increases from 293 K to 353 K, which is an increase by a factor of 1.205. The resistance of the carbon resistor therefore increases by the same factor.

Answer 2

Carbon's temperature coefficient of reistance is -.0005.  Ref: http://hyperphysics.phy-astr.gsu.edu/hba...

R = R_ref (1 + C(T-T_ref)

R = (200 Ohm) ( 1 + (-.0005)(80 -20)

R = 200Ohm ( 1 - 0.03)

= 194 Ohm