$A$ Carnot engine whose efficiency is $40 \%$,receives heat at $500 \ K$. If the efficiency is to be $50 \%$,the source temperature for the same exhaust temperature is (in $K$)

Efficiency of a heat engine whose sink is at temperature of $300 \,K$ is $40 \%$. To increase the efficiency to $60 \%$, keeping the sink temperature constant, the source temperature must be increased by (in $\,K$)

$A$ heat engine has an efficiency of $\frac{1}{6}$. When the temperature of the sink is reduced by $62^{\circ}C$,its efficiency gets doubled. The temperature of the source is $.....^{\circ}C$.

$A$ Carnot engine $(E)$ is working between two temperatures $473 \ K$ and $273 \ K$. In a new system,two engines are used: engine $E_1$ works between $473 \ K$ and $373 \ K$,and engine $E_2$ works between $373 \ K$ and $273 \ K$. If $\eta_{12}$,$\eta_1$,and $\eta_2$ are the efficiencies of the engines $E$,$E_1$,and $E_2$ respectively,then:

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

$A$ number of Carnot engines are operated at identical cold reservoir temperatures $(T_{L})$. However,their hot reservoir temperatures are kept different. $A$ graph of the efficiency of the engines versus hot reservoir temperature $(T_{H})$ is plotted. The correct graphical representation is