Answer to Question #6445 in Electric Circuits for Rose
A coffee cup heater and a lamp are connected in parallel to the same 120 V outlet. Together, they use a total of 87 W of power. The resistance of the heater is 4.00 X 10^2Ω . Find the resistance of the lamp.
Let R1=400Ω be a resistance of the heater, and R2 be the resistance of the lamp, I1, and I2 be respectively the currents through heater and lamp respecively, V=120V be the outlet, and P=87W be the total power which use the heater and the lamp.
Since the heater and a lamp are connected in parallel it follows that the total current is I = I1+I2, where I1 = U/R1 I2 = U/R2