The efficiency of a Carnot engine is $100\%$ if

$A$ Carnot engine whose sink is at $300 \, K$ has an efficiency of $50 \%$. By how much should the temperature of the source be increased so that the efficiency becomes $70 \%$?

An ideal gas heat engine operates in a Carnot cycle between $227^{\circ}C$ and $127^{\circ}C$. It absorbs $6\,kcal$ at the higher temperature. The amount of heat (in $kcal$) converted into work is equal to

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

Two Carnot engines $A$ and $B$ operate in series such that engine $A$ absorbs heat $Q_1$ at temperature $T_1$ and rejects heat $Q$ to a sink at temperature $T$. Engine $B$ absorbs half of the heat rejected by engine $A$ (i.e.,$Q/2$) and rejects heat $Q_3$ to the sink at temperature $T_3$. When the work done in both cases is equal,the value of $T$ is:

$A$ Carnot engine operating between temperatures $7^{\circ}C$ and a higher temperature has an efficiency of $50\%$. To increase its efficiency to $70\%$,by how much must the temperature of the source be increased in $K$?