If source is at a temperature $T_1$ and sink is at a temperature $T_2$, the efficiency of the Carnot engine is maximum when

• A

  $T_1$ and $T_2$ are equal
• B

  $T_1$ is low and $T_2$ is high
• Correct answer
  C

  $T_1$ is high and $T_2$ is low
• D

  Both $T_1$ and $T_2$ are high

Hence, the correct answer is option: 'C'.