Temperature of sink; $T_2=300 K$
Original efficiency; $\eta=50 \%=0.5$
Let initial temperature $: \rightarrow T_1$
we know; $\eta=1-\frac{T_2}{T_1}$
Substituting the values we get:
$0.5=1-\frac{300}{T_1}$
$\Rightarrow T_1=600\,K$
Now; new efficiency; $\eta^{\prime}=70 \%=.7$
New initial temperature $=T_1^{\prime}$
$\Rightarrow 0.7=1-\frac{T_2}{\left(T_1\right)^{\prime}}$
$\Rightarrow 0.7=1-\frac{300}{\left(T_1\right)^{\prime}}$
$\Rightarrow\left(T_1\right)^{\prime}=1000\,K$
$\therefore$ Increase in source temperature is:
$\Delta T =(1000-600)\,K$
$\Rightarrow \Delta T =400\,K$
So the temperature of the source should be increased by $400\,K$.



In a thermodynamics process on an ideal monatomic gas, the infinitesimal heat absorbed by the gas is given by $T \Delta X$, where $T$ is temperature of the system and $\Delta X$ is the infinitesimal change in a thermodynamic quantity $X$ of the system. For a mole of monatomic ideal gas
$X=\frac{3}{2} R \ln \left(\frac{T}{T_A}\right)+R \ln \left(\frac{V}{V_A}\right)$. Here, $R$ is gas constant, $V$ is volume of gas, $T_A$ and $V_A$ are constants.
The $List-I$ below gives some quantities involved in a process and $List-II$ gives some possible values of these quantities.
| List-$I$ | List-$II$ |
| $(I)$ Work done by the system in process $1 \rightarrow 2 \rightarrow 3$ | $(P)$ $\frac{1}{3} R T_0 \ln 2$ |
| $(II)$ Change in internal energy in process $1 \rightarrow 2 \rightarrow 3$ | $(Q)$ $\frac{1}{3} RT _0$ |
| $(III)$ Heat absorbed by the system in process $1 \rightarrow 2 \rightarrow 3$ | $(R)$ $R T _0$ |
| $(IV)$ Heat absorbed by the system in process $1 \rightarrow 2$ | $(S)$ $\frac{4}{3} RT _0$ |
| $(T)$ $\frac{1}{3} RT _0(3+\ln 2)$ | |
| $(U)$ $\frac{5}{6} RT _0$ |
If the process carried out on one mole of monatomic ideal gas is as shown in figure in the PV-diagram with $P _0 V _0=\frac{1}{3} RT _0$, the correct match is,
$(1)$$I \rightarrow Q, II \rightarrow R , III \rightarrow P , IV \rightarrow U$
$(2)$ $I \rightarrow S , II \rightarrow R , III \rightarrow Q , IV \rightarrow T$
$(3)$ $I \rightarrow Q , II \rightarrow R , III \rightarrow S , IV \rightarrow U$
$(4)$ $I \rightarrow Q , II \rightarrow S , III \rightarrow R , IV \rightarrow U$
($2$) If the process on one mole of monatomic ideal gas is an shown is as shown in the $TV$-diagram with $P _0 V _0=\frac{1}{3} RT _0$, the correct match is
$(1)$ $I \rightarrow S, II \rightarrow T, III \rightarrow Q , IV \rightarrow U$
$(2)$ $I \rightarrow P , II \rightarrow R, III \rightarrow T , IV \rightarrow S$
$(3)$ $I \rightarrow P, II \rightarrow, III \rightarrow Q, IV \rightarrow T$
$(4)$ $I \rightarrow P, II \rightarrow R, III \rightarrow T, IV \rightarrow P$
Give the answer or quetion $(1)$ and $(2)$