Suppose two resistors of impedance r1 and r2 are placed in series and held at different physical temperatures 
We would like to model this series combination of noisy resistors as a single noiseless resistor with an impedance of 
together with a noise source with an effective temperature of . In short, we want the two models shown in the accompanying figure to be equivalent.
Assuming the noise produced by the two resistors is independent, what should , the effective noise temperature of the series combination of resistors, be? If the two resistors are held at the same physical temperature, is the effective temperature equal to the true common temperature of the resistors?
