# Homework Help: Power loss in transmission lines (Electromagnetic Induction and Faraday's Law)

1. Mar 20, 2006

### confusedbyphysics

Show that the power loss in transmission lines, PL, is given by PL = (PT)^2 X R/(V^2), where PT is the power trasmitted to the user, V is the delivered voltage, and R is the resistance to the power lines.

I don't even know where to start. Im so confused by this chapter, I don't know what this question has to do with magnetic flux and Lenz's law and the other stuff in the chapter. Any help please?? :surprised

2. Mar 20, 2006

### nrqed

It has nothing to do with Lenz law or flux, indeed.

Think of a simple circuit with two resistors (representing the resistance of the line and the resistance of the load (where the user is drawing power from).

You have $P_L = R_1 I^2$ and $P_T = R_2 I^2$ where $R_1$ is the resistance of the lines. You also have $V = R_2 I$ where V is the voltage delivered to the user. Use the last two equations to isolate I and plug in the first and you will get the answer. (also, you could use directly $P_T = V I$ which gets you to the answer faster).

Pat