Question

A carnot cycle has an efficiency of 40% its low temperature reservoir is at 7 degree Celsius what is the temperature of source

Answer 1

For a Carnot engine, 

Eff = 1 - Tc/Th 

where 

Tc = cold reservoir temperature 
Th = hot reservoir temperature 

For an efficiency of 40%, then 

0.40 = 1 - (7 + 273)/Th 

NOTE - temperature must be converted to the absolute Kelvin scale 

0.40 = 1 - 280/Th 

0.60Th = 280

Th = 466.66 K = 466.66 - 273 

Th = 193.66 C