If the temperature of the sink is at absolute zero,then the efficiency of the Carnot engine will be ........ $\%$

$A$ Carnot engine has an efficiency of $50\%$ when its source is at a temperature $327^{\circ}C$. The temperature of the sink is $.........^{\circ}C$.

An ideal heat engine exhausts heat at $77\,^{\circ}C$. To have a $30\%$ efficiency,it must take heat at what temperature in $^{\circ}C$?

An engine operating between the boiling and freezing points of water will have:
$1.$ Efficiency more than $27 \%$
$2.$ Efficiency less than the efficiency of a Carnot engine operating between the same two temperatures.
$3.$ Efficiency equal to $27 \%$
$4.$ Efficiency less than $27 \%$

$A$ frictionless heat engine can be $100 \%$ efficient only if its exhaust temperature is ............

Two Carnot engines $A$ and $B$ are operated in succession. The first one,$A$,receives heat from a source at $T_1 = 800 \ K$ and rejects heat to a sink at $T_2 \ K$. The second engine,$B$,receives the heat rejected by the first engine and rejects heat to another sink at $T_3 = 300 \ K$. If the work outputs of the two engines are equal,then the value of $T_2$ is .... $K$.