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Electricity can be transmitted either at 240V or at 24000V using a step-up transformer.

The cables have total resistance of 0.4W

What is the power loss when voltage is transmitted at:

1) 240V

2) 24000V

I AM SURE YOU CAN WORK THIS OUT USING I squared R (or as I have typed it: I^2R)

Using 240V:

P = IV, therefore I = 500A

P = I^2R = 100000W

Using 24000V:

P = IV, 120000W = I24000V, therefore I = 5A

P = I^2R = 10A

Less power loss when using higher voltage

My question begins with the premises called Ohm’s law and Joules’ law which lead to the textbook equations I^2R = V^2/R = P

Power loss using I^2R works out different to power loss using V^2/R, given all text books equate I^2R with V^2/R

THIS FAILS TO WORK WITH ABOVE QUESTION!

Infact P=V^/R indicates greater power loss at higher voltages (for same resistance), negating the idea of stepping up voltages to reduce power loss in electrical transmission. In your solution please using the values I have used above in the question (taken from a text book)

Please clarify - at a level for 16-18 year old physics students. Thanks.

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# Homework Help: How to calculate power loss in transmission cables?

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