• # question_answer The efficiency of a carnot engine is given as 0.75. If the cycle directions is reversed, what will be the valve of C.O.P. for the carnot refrigerator? A) 0.27                             B) 0.33C) 1.27                             D) 2.33

${{\eta }_{HE}}=1-=\frac{{{T}_{2}}}{{{T}_{1\,}}}=0.75\,\,or\,\,\frac{{{T}_{2}}}{{{T}_{1}}}=0.25$ ${{(COP)}_{\operatorname{Re}f}}=\frac{{{T}_{2}}}{{{T}_{1}}-{{T}_{2}}}=\frac{({{T}_{2}}/{{T}_{1}})}{1-({{T}_{1}}/{{T}_{1}})}=\frac{0.25}{1-0.25}$             $=\frac{0.25}{0.75}=\frac{1}{3}=0.33$