# Homework Help: Efficiency - how to get the maximum efficiency in a circuit?

1. Mar 3, 2014

### alexmath

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.

2. Mar 3, 2014

### BvU

Hello Lex,
What is the question ? How to most efficiently do what exactly ?

3. Mar 3, 2014

### CWatters

More details are required.

Both are 100% efficient if the wanted output is heat.

Both are 0% efficient if the wanted output is light (because there is no light bulb or LED in the circuit as described so far).