We learnt in high school that according to Ohm's law V/I=R. We also learnt that during power transmission in an electric line P=VI and that in order to minimize loss voltage is raised. As a consequence current is reduced. This contradicts with the Ohm's law which states that V is proportional to I. What is the difference?
Answer
The usable voltage out of a battery or a generator is V=E−iRwire where E is the rated voltage (being 12V or 768kV), i is the current and Rwire is the resistance of the wire. The current is usually found by the load on the circuit as i=VRload.
So alltogether with power P=iV we have
V=ERloadRload+RwireP=E2Rload(Rload+Rwire)2
Only when the wire resitance is negligible you get V=EP=V2Rload
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