An average of 120 kW of electric power is sent to a small town from a power plant 10 km away. The transmission lines have a total resistance of 0.40 ohms. Calculate the power loss if the power is transmitted at 240 V. The solution is I=P/V=500 A, then the power loss in the lines, P(loss)=I^2R=(500A)^2*0.04ohms=100kW Here I don't understand why Ploss=I^2*R? I mean is that supposed to be power output, so then in order to find the power loss, we need to use Power input 120kW-output 100kW, then 20 is the power loss?!! Because when I see 'loss', it's like a common sense to use subtraction, but how come here is not? thanks for help.