Question

A carbon resistor dissipates 60 W of power from a 120 V source at 20°C. How much power will be dissipated in the resistor at 120°C if connected across the same source? Assume the temperature coefficient of carbon at 20°C is -0.0005 per °

Answer 1

$P=U^2/R\to R=U^2/P=120^2/60=240\ (\Omega)$

$R=R_0(1+\alpha t) \to240=R_0(1-0.0005\cdot20) \to$

$R_0=242.42\ (\Omega)$

$R_1=242.42\cdot(1-0.0005\cdot120)=227.87(\Omega)$

$P_1=120^2/227.87=63.2\ (W)$ . Answer