# Homework Help: Question about Units

1. Jun 22, 2006

### sophzilla

I solved the problem, but I can't get the right unit for the answer.

A Carnot engine whose low-temperature reservoir is at 16°C has an efficiency of 31%. By how much should the temperature of the high-temperature reservoir be increased to increase the efficiency to 70%?

My numerical answer is 544.8. I tried Kelvin first - the most obvious choice - but that was wrong. Then I tried celcius and J/K.

I tried to work it out but I have no earthly idea - the other choices include:
- C0 (like the celcius sign but the circle is after the C)
-J/kg*K
-J/mol*K and
-kJ/kg

Any help would be grately appreciated.

2. Jun 22, 2006

### Andrew Mason

You have to use Kelvin for temperature in thermodynamics. I get 544.5 K as the increase (from 418.8 K to 963.33 K)

AM

3. Jun 22, 2006

### sophzilla

Well...the thing is, I did use Kelvin. That was my first choice, but it was wrong. Any other sound possibilities?

4. Jun 22, 2006

### Andrew Mason

Mind you, this temperature difference is also 544.5 degrees Celsius. It is just that you have to work out the thermodynamics part in K and then convert back to Celsius.

AM