$A$ Carnot's engine has an efficiency of $25 \%$ when its sink is at $27^{\circ} C$. If it has to be increased to $40 \%$,what should be the temperature of the sink keeping the temperature of the source constant (in $K$)?

The efficiency of a Carnot engine operating between reservoirs maintained at temperatures $27^{\circ}C$ and $-123^{\circ}C$ is ...... $\%$

Temperature of a cold reservoir of a Carnot engine is $127^{\circ} C$. If the efficiency of the Carnot engine is $20 \%$,then the temperature of the hot reservoir is (in $^{\circ} C$)

Two Carnot engines $A$ and $B$ are operated in series. Engine $A$ receives heat from a reservoir at $600\,K$ and rejects heat to a reservoir at temperature $T$. Engine $B$ receives heat rejected by engine $A$ and in turn rejects it to a reservoir at $100\,K$. If the efficiencies of the two engines $A$ and $B$ are equal,what is the value of the intermediate temperature $T$ and the ratio of their efficiencies $\frac{\eta_A}{\eta_B}$?

$A$ Carnot engine, whose efficiency is $40\%$, takes heat from a source maintained at temperature $600\text{ K}$. To have an efficiency of $60\%$, the intake temperature for the same exhaust temperature should be: (in $\text{ K}$)

$A$ Carnot engine with its cold body at $17\,^{\circ}C$ has $50\%$ efficiency. If the temperature of its hot body is now increased by $145\,^{\circ}C$,the efficiency becomes...... $\%$