Homework Help: Physics (DUE SOON)

Posted by DCM on Monday, February 13, 2012 at 5:24pm.

A generating station is producing 2.00 106 W of power that is to be sent to a small town located 7.0 km away. Each of the two wires that comprise the transmission line has a resistance per kilometer of length of 5.00 10-2 /km.
(a) Find the power lost in heating the wires if the power is transmitted at 1300 V.

W

(b) A 120:1 step-up transformer is used to raise the voltage before the power is transmitted. How much power is now lost in heating the wires?
W

Physics (DUE SOON) - Damon, Monday, February 13, 2012 at 5:35pm
I did this yesterday for someone:

Power = V i = 1300 * i = 2*10^6
so
i = (2/1.3)*10^3 = 1.54 * 10^3 amps (big current!)

R = 2 * 7 * 5 * 10^-2 = .7 Ohms

Power loss = i^2 R = (1.54)^2*10^6*.7 = 1.66*10^6 Watts (we lose about as much as we use)
-------------------
Now use a high voltage line
i = 1.54*10^3/120 = 12.8 amps (reasonable now)

power loss = i^2 R = 12.8^2 (.7) = 115 Watts, about a 100 watt light bulb worth lost now.

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