Heat

[ROOP]

why do we use kelvin scale while doing numericals on carnot's engine?

[swansont]

The theory is based on using an absolute temperature scale. (For temperature differences it doesn't matter, since the offset cancels in the subtraction)

[CaptainPanic]

why do we use kelvin scale while doing numericals on carnot's engine?

Because that's how it was derived.

 

If you use another scale, results don't make sense (you can get negative efficiencies, or efficiencies higher than 100%).

 

The definition of "zero Kelvin = absolute lowest temperature" was part of the derivation of the formulas.