A Carnot engine with sink temperature at 170C has 50% efficiency. By how much should its source temperature be changed to increase its efficiency to 60%?

η=1−T2T1 Initially,          50100=1−273+17T1 or                   290T1=12  or T1=580K Finally,            60100=1−273+17T1'  or  290T1' =25 or                        T'=725K  ∴       Change in source temperature                              =(725−580)K=145K