$A$ 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 $K$)?

Who first proposed (invented) the Carnot engine?

$A$ Carnot engine with efficiency $50\,\%$ takes heat from a source at $600\,K$. In order to increase the efficiency to $70\,\%$,keeping the temperature of the sink the same,the new temperature of the source will be $.........\,K$.

The first operation involved in a Carnot cycle is

$A$ Carnot engine has an efficiency of $50 \%$. If the temperature of the sink is reduced by $40 \, K$,its efficiency increases by $30 \%$. The temperature of the source will be $.... \, K$.

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 .... $K$.