efficiency -- how to get the maximum efficiency in a circuit? 1. The problem statement, all variables and given/known data I don't quite understand how to get the maximum efficiency in a circuit. Exemple. 4 Volts and 2.0Ω will produce 8 watts with a current of 2.0 amps. 5 Volts and 3.1Ω will produce 8 watts with a current of 1.6 amps. There are infinitely ways to do so. Also we have an led which has to be connected. 2. Relevant equations P=UI=I^2*R=U^2/R 3. The attempt at a solution My intuition says that the first one is more efficient, but the battery will drain faster. I realy want to know how to mix this information together for my circuit.