A fundamental concept that i have learned from basic electrical circuit study is to receive maximum power by a load of resistance RL from a source the necessary condition is RL = Rin where Rin is the input resistance seen by the load. This is called maximum power transfer theorem. But the efficiency in this condition is 50%.
Then it is said that, the maximum power transfer condition is the best choice to transmit signal in communication system. Since we need the signal with maximum strength at the receiving end.
But in power transmission we target to receive as much higher efficiency as possible. That's why maximum power transfer condition is not a desirable feature in this case.
My question is, whether the above two paragraphs are true or not? If true then, why maximum receiving power wouldn't be a desirable feat for electricity transmission?
Best Answer
Those statements are true. But I see what bothers you. You have to imagine it like this:
In Wireless transmission one wants to make the highest loss possible since this loss will actually be the power of the transmitted signal. This is a very easy optimization problem which will lead to the fact you have stated $$R_L = R_{in}.$$
In power transmission however the goal is to be as efficient as possible. This will still lead to the fact that the highest power output is achieved with $$R_L = R_{in}.$$ But thats the maximum you could get out e.g. of a transformer. You don't want it to operate in this point. Instead you lay out your transformer in such a way that it won't reach this point. Then the efficiency is much higher but you won't be using its full potential.
You might have noticed this when e.g. trying to charge a tablet with phone charger. It may works and the charger maxes out, but it gets hot since much energy is converted to heat because of the high internal loss. (Keep in mind that a phone charger is not only a transformer). You take a bigger charger which won't max out, is may oversized but has a higher efficiency.
The theorem was originally misunderstood (notably by Joule) to imply that a system consisting of an electric motor driven by a battery could not be more than 50% efficient since, when the impedances were matched, the power lost as heat in the battery would always be equal to the power delivered to the motor.
This is also good explained in Wikipedia: