The value of efficiency $\eta$ for a heat engine may lie between

In the Carnot engine, when heat is taken from the source, the temperature of the source

Three Carnot engines operate in series between a heat source at a temperature $T_1$ and a heat sink at temperature $T_4$ (see figure). There are two other reservoirs at temperatures $T_2$ and $T_3$,as shown,with $T_1 > T_2 > T_3 > T_4$. The three engines are equally efficient if

The ratio of the efficiencies of two Carnot engines $A$ and $B$ is $1.25$. The temperature difference between the source and the sink is the same in both engines. The ratio of the absolute temperatures of the sources of engines $A$ and $B$ is

$A$ Carnot engine $C_1$ operates between temperatures $T_1$ and $T_2$ $(T_1 > T_2)$. $A$ second Carnot engine $C_2$ uses all the heat rejected by the engine $C_1$ and operates between temperatures $T_2$ and $T_3$ (where $T_2 > T_3$). The efficiency of this combined ($C_1$ and $C_2$ together) engine is

$A$ Carnot engine operates between $300 \ K$ and $600 \ K$. If the work done per cycle is $800 \ J$,then the heat supplied per cycle is ....... $J/cycle$.