# Homework Help: Machine A and machine B are performing the same task

1. Aug 6, 2013

### edwin.07

1. Machine A and machine B are performing the same task. Machine A is causing twice the entropy change of machine B. Which would you rather use and why?

3. I would choose Machine B. Lots of disorder = high entropy, while order = low entropy.

2. Aug 7, 2013

### Staff: Mentor

Why do you prefer order (and where)? ;)
I think we have to assume that the product is the same in both cases, otherwise it clearly depends on the quality of the product.

3. Aug 8, 2013

### CWatters

It says "entropy change" not "entropy increase" or "entropy decrease". Presumably the "change" is in the required direction or you wouldn't use either machine!

So I would choose machine A as it appears to be twice as effective at doing what you want.

4. Aug 8, 2013

### Staff: Mentor

I think edwin.07 correctly identified the direction the total entropy of the system has to take.
If those entropy changes are meant for specific parts of the setup only, the question becomes very unclear.

5. Aug 9, 2013

### CWatters

Ok yes. The total entropy of a closed system only ever increases. So if the entropy of the wanted output is the same for both then the extra entropy created by machine A must represent extra losses/inefficiency.

6. Aug 9, 2013

### 256bits

The choice depends upon how you want to define 'the same task' - ie is it a single task or repetative?

Machine A could be two machine B's working in tandem.
Then which do you choose?
and why?

Last edited: Aug 9, 2013