Given, sink temperature, T2=27°C=300K Case I Efficiency, η1=40% Case II Efficiency, η2=60% Let temperature of source in two cases be T1 and T′1. As we know that, η1=1−
T2
T1
⇒
40
100
=1−
300
T1
⇒T1=500K and η2=1−
T2
T′1
60
100
=1−
300
T′1
⇒
300
T′1
=
40
100
⇒T′1=750K ∴ Change is temperature, ΔT=T′1−T1=750−500=250K