Question 257: Thermodynamics & KTG

Question

In $1^{	ext {st }}$ case, Carnot engine operates between temperatures $300 \mathrm{~K}$ and $100 \mathrm{~K}$. In $2^{	ext {nd }}$ case, as shown in the figure, a combination of two engines is used. The efficiency of this combination (in $2^{	ext {nd }}$ case) will be :
![](https://app-content.cdn.examgoal.net/fly/@width/image/1l6qq6ny9/4a6d093b-2fcf-47a2-a242-e11f32231e53/b1d48c00-1a61-11ed-90e9-e993c844f460/file-1l6qq6nya.png?format=png)

Accepted Answer

${\eta _{net}} = {{{W_1} + {W_2}} \over {{Q_1}}}$
${\eta _{net}} = {{{W_1}} \over {{Q_1}}} + {{{W_2}} \over {{Q_1}}}$
${\eta _{net}} = {\eta _1} + {{{W_2}} \over {{Q_2}}} 	imes {{{Q_2}} \over {{Q_1}}}$
${\eta _{net}} = {\eta _1} + ({\eta _2})(1 - {\eta _1})$
$1 - {\eta _1} < 1$
$ \Rightarrow {\eta _{net}} < {\eta _1} + {\eta _2}$

Answer

same as the $1^{	ext {st }}$ case.

Answer

always greater than the $1^{	ext {st }}$ case.

Answer

always less than the $1^{	ext {st }}$ case.

Answer

may increase or decrease with respect to the $1^{	ext {st }}$ case.

Thermodynamics & KTG

In 1^{\text{st }} case, Carnot engine operates between temperatures 300 \mathrm{~K} and 100 \mathrm{~K}. In 2^{\text{nd }} case, as shown in the figure, a combination of two engines is used. The efficiency of this combination (in 2^{\text{nd }} case) will be :

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