<!DOCTYPE html> <!DOCTYPE html> <html lang="en"> <html lang="en"> <head> <head> <meta charset="utf-8"> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="content-language" content="en"> <meta http-equiv="content-language" content="en"> <meta name="keywords" content="Savchenko Problems in Physics, Savchenko solutions, physics problems, physics olympiad preparation, IPhO, Jaan Kalda"> <meta name="keywords" content="Savchenko Problems in Physics, Savchenko solutions, physics problems, physics olympiad preparation, IPhO, Jaan Kalda"> <meta name="description" content="Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas."> <meta name="description" content="Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas."> <meta name="author" content="Aliaksandr Melnichenka"> <meta name="author" content="Aliaksandr Melnichenka"> <meta name="date" content="2023-10" scheme="YYYY-MM"> <meta name="date" content="2023-10" scheme="YYYY-MM"> <meta property="og:title" content="Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas."> <meta property="og:title" content="Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas."> <meta property="og:image" content="img/logo.png"> <meta property="og:image" content="img/logo.png"> <meta property="og:description" content="Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas."> <meta property="og:description" content="Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas."> <meta name="yandex-verification" content="6cfda41f74038368"> <meta name="yandex-verification" content="6cfda41f74038368"> <title> Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas.</title> <title> Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas.</title> <link rel="stylesheet" href="../../css/css-latex/style.css"> <link rel="stylesheet" href="../../css/css-latex/style.css"> <link rel="icon" href="../../img/logo.png" type="image/png"> <link rel="icon" href="../../img/logo.png" type="image/png"> <script src="../../js/jquery-1.10.1.min.js"></script> <script src="../../js/jquery-1.10.1.min.js"></script> <script async src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.7/MathJax.js?config=TeX-MML-AM_CHTML"></script> <script async src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.7/MathJax.js?config=TeX-MML-AM_CHTML"></script> <script type="text/x-mathjax-config"> <script type="text/x-mathjax-config"> MathJax.Hub.Config({ MathJax.Hub.Config({ extensions: ['tex2jax.js'], extensions: ['tex2jax.js'], jax: ['input/TeX', 'output/HTML-CSS'], jax: ['input/TeX', 'output/HTML-CSS'], tex2jax: { tex2jax: { inlineMath: [['$ ', ' $ '], ['$ ', ' $ ']], inlineMath: [['$ ', ' $ '], ['$ ', ' $ ']], processEscapes: true, processEscapes: true, processClass: 'tex2jax', processClass: 'tex2jax', ignoreClass: 'html' ignoreClass: 'html' }, }, showProcessingMessages: false, showProcessingMessages: false, messageStyle: 'none' messageStyle: 'none' }); }); </script> </script> </head> </head> <body style=""> <body style=""> <header style="text-align:center;"> <header style="text-align:center;"> <a href="../../" style="text-decoration: none;"> <a href="../../" style="text-decoration: none;"> <div id="logo"> <div id="logo"> <span><img src="../../img/book.png"></span><span> Savchenko Solutions</span> <span><img src="../../img/book.png"></span><span> Savchenko Solutions</span> </div> </div> </a> </a> <p class="author"> <p class="author"> Solutions of Savchenko Problems in Physics <br> Solutions of Savchenko Problems in Physics <br> <i><b> knowledge must be free</b></i> <i><b> knowledge must be free</b></i> </p> </p> </header> </header> <h3 id="back-link"><a href="../../#5.9"> $ \leftarrow $ Back</a></h3> <h3 id="back-link"><a href="../../#5.9"> $ \leftarrow $ Back</a></h3> <h3> Statement </h3> <h3> Statement </h3> <p> <p> $ 5.9.10^* $ $ 5.9.10^* $ Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas. Find the efficience of cycles shown in following figures, if as power agent it is taken a monoatomic ideal gas. </p> </p> <center> <center> <figure> <figure> <img src="statement.png" <img src="statement.png" loading="lazy" alt="5.9.10" width="350" /> loading="lazy" alt="5.9.10" width="350" /> <figcaption> <figcaption> For problem 5.9.10 For problem 5.9.10 </figcaption> </figcaption> </figure> </figure> </center> </center> <h3> Solution</h3> <h3> Solution</h3> <p> <p> a) Let enumerate the states from 1 to 4 in clockwise sense starting in the coordinate $ (P_1,V_1) $ . The efficience is defined as a) Let enumerate the states from 1 to 4 in clockwise sense starting in the coordinate $ (P_1,V_1) $ . The efficience is defined as $$ \eta = 1- \frac { |Q_c| }{ Q_h } =1- \frac { |Q_ { 34 } | }{ Q_ { 12 }} \quad (1) $$ $$ \eta = 1- \frac { |Q_c| }{ Q_h } =1- \frac { |Q_ { 34 } | }{ Q_ { 12 }} \quad (1) $$ where $ Q_ { 34 } $ is the heat released by gas (cold reservoir) and $ Q_ { 12 } $ is the heat absorbed by gas (hot reservoir), while $ Q_ { 23 } $ and $ Q_ { 41 } $ are zero (adiabatic processes). Since $ 3-4 $ is an isochoric process, where $ Q_ { 34 } $ is the heat released by gas (cold reservoir) and $ Q_ { 12 } $ is the heat absorbed by gas (hot reservoir), while $ Q_ { 23 } $ and $ Q_ { 41 } $ are zero (adiabatic processes). Since $ 3-4 $ is an isochoric process, $$ Q_ { 34 } = \Delta U_ { 34 } = nC_v \left (T_4-T_3 \right ) \quad (2) $$ $$ Q_ { 34 } = \Delta U_ { 34 } = nC_v \left (T_4-T_3 \right ) \quad (2) $$ From Poisson Law From Poisson Law $$ P_1V_1^ \gamma = P_4V_2^ \gamma $$ $$ P_1V_1^ \gamma = P_4V_2^ \gamma $$
@@ -75,23 +75,23 @@
and the state 4 is characterized by
and the state 4 is characterized by
$$ P_4V_2=nRT_4 $$
$$ P_4V_2=nRT_4 $$
So, separating $ P_4 $ and putting it into above Poisson law
So, separating $ P_4 $ and putting it into above Poisson law
$$ T_4 = \frac { P_1V_1^ \gamma }{ nRV_2^ { \gamma -1 }} \quad (3) $$
$$ T_4 = \frac { P_1V_1^ \gamma }{ nRV_2^ { \gamma -1 }} \quad (3) $$
Proceeding similarly, $ T_3 $ can be found. Applying Poisson Law for process $ 2-3 $ ,
Proceeding similarly, $ T_3 $ can be found. Applying Poisson Law for process $ 2-3 $ ,
$$ P_2V_1^ \gamma =P_3V_2^ \gamma $$
$$ P_2V_1^ \gamma =P_3V_2^ \gamma $$
State equation for state 3 is
State equation for state 3 is
$$ P_3V_2=nRT_3 $$
$$ P_3V_2=nRT_3 $$
Separating $ P_3 $ and substituting into respective Poisson Law
Separating $ P_3 $ and substituting into respective Poisson Law
$$ T_3 = \frac { P_2V_1^ \gamma }{ nRV_2^ { \gamma -1 }} \quad (4) $$
$$ T_3 = \frac { P_2V_1^ \gamma }{ nRV_2^ { \gamma -1 }} \quad (4) $$
Substituting $ (3) $ and $ (4) $ into $ (2) $ , and as $ C_v=iR/2 $
Substituting $ (3) $ and $ (4) $ into $ (2) $ , and as $ C_v=iR/2 $
$$ Q_ { 34 } = \frac { i }{ 2 } \frac { V_1^ \gamma }{ V_2^ { \gamma -1 }} \left (P_1-P_2 \right ) \quad (5) $$
$$ Q_ { 34 } = \frac { i }{ 2 } \frac { V_1^ \gamma }{ V_2^ { \gamma -1 }} \left (P_1-P_2 \right ) \quad (5) $$
For the process $ 1-2 $
For the process $ 1-2 $
$$ Q_ { 12 } = \Delta U_ { 12 } = nC_v \left (T_2-T_1 \right ) $$
$$ Q_ { 12 } = \Delta U_ { 12 } = nC_v \left (T_2-T_1 \right ) $$
Taking account the state equations for states 1 and 2, temperatures can be found,
Taking account the state equations for states 1 and 2, temperatures can be found,
$$ Q_ { 12 } =nC_v \left ( \frac { P_2V_1 }{ nR } - \frac { P_1V_1 }{ nR } \right ) $$
$$ Q_ { 12 } =nC_v \left ( \frac { P_2V_1 }{ nR } - \frac { P_1V_1 }{ nR } \right ) $$
$$ Q_ { 12 } = \frac { i }{ 2 } V_1 \left (P_2-P_1 \right ) \quad (6) $$
$$ Q_ { 12 } = \frac { i }{ 2 } V_1 \left (P_2-P_1 \right ) \quad (6) $$
Putting $ (5) $ and $ (6) $ into $ (1) $
Putting $ (5) $ and $ (6) $ into $ (1) $
$$ \eta = 1- \left ( \frac { V_1 }{ V_2 } \right )^ { \gamma -1 } $$
$$ \eta = 1- \left ( \frac { V_1 }{ V_2 } \right )^ { \gamma -1 } $$
Since $ \gamma =C_p/C_v=1+2/i $ and $ i=3 $ (monoatomic gas),
Since $ \gamma =C_p/C_v=1+2/i $ and $ i=3 $ (monoatomic gas),
$$ \boxed { \eta = 1- \left ( \frac { V_1 }{ V_2 } \right )^ { \frac { 2 }{ 3 }}} $$
$$ \boxed { \eta = 1- \left ( \frac { V_1 }{ V_2 } \right )^ { \frac { 2 }{ 3 }}} $$
b) Let enumerate again the states following a clockwise way, this time starting in coordinate $ (P_1,T_1) $ . The efficience is
b) Let enumerate again the states following a clockwise way, this time starting in coordinate $ (P_1,T_1) $ . The efficience is
$$ \eta = 1- \frac { |Q_c| }{ Q_h } \quad (I) $$
$$ \eta = 1- \frac { |Q_c| }{ Q_h } \quad (I) $$
For identifying correctly the reservoirs, let's see the following graph corresponding to the cycle in a $ P $ vs $ V $ plot. For identifying correctly the reservoirs, let's see the following graph corresponding to the cycle in a $ P $ vs $ V $ plot. </p> </p> <center> <center> <figure> <figure> <img src="PVb.png" <img src="PVb.png" loading="lazy" alt="5.9.10" width="300" /> loading="lazy" alt="5.9.10" width="300" /> <figcaption> <figcaption> $ P $ vs $ V $ plot $ P $ vs $ V $ plot </figcaption> </figcaption> </figure> </figure> </center> </center> <p> <p> The hot reservoir is defined as The hot reservoir is defined as $$ Q_h = Q_ { 23 } + Q_ { 34 } \quad (II) $$ $$ Q_h = Q_ { 23 } + Q_ { 34 } \quad (II) $$ and cold one and cold one $$ Q_c = Q_ { 12 } + Q_ { 41 } \quad (III) $$ $$ Q_c = Q_ { 12 } + Q_ { 41 } \quad (III) $$ Process $ 2-3 $ is isobaric, then Process $ 2-3 $ is isobaric, then $$ Q_ { 23 } =nC_p \left (T_2-T_1 \right ) \quad (IV) $$ $$ Q_ { 23 } =nC_p \left (T_2-T_1 \right ) \quad (IV) $$ Process $ 3-4 $ is isothermal, so Process $ 3-4 $ is isothermal, so $$ Q_ { 34 } = A_ { 34 } = nRT_2 \ln { \frac { V_4 }{ V_3 }} $$ $$ Q_ { 34 } = A_ { 34 } = nRT_2 \ln { \frac { V_4 }{ V_3 }} $$ Since $ V=nRT/P $ according state equation Since $ V=nRT/P $ according state equation $$ Q_ { 34 } = nRT_2 \ln { \frac { P_2 }{ P_1 }} \quad (V) $$ $$ Q_ { 34 } = nRT_2 \ln { \frac { P_2 }{ P_1 }} \quad (V) $$ Substituting $ (IV) $ and $ (V) $ into $ (II) $ and taking account that $ C_p=(i+2)R/2 $ Substituting $ (IV) $ and $ (V) $ into $ (II) $ and taking account that $ C_p=(i+2)R/2 $ $$ Q_h = \frac { i+2 }{ 2 } nR \left (T_2-T_1 \right )+nRT_2 \ln { \frac { P_2 }{ P_1 }} \quad (VI) $$ $$ Q_h = \frac { i+2 }{ 2 } nR \left (T_2-T_1 \right )+nRT_2 \ln { \frac { P_2 }{ P_1 }} \quad (VI) $$ Process $ 1-2 $ is isothermal, so Process $ 1-2 $ is isothermal, so $$ Q_ { 12 } =A_ { 12 } =nRT_1 \ln { \frac { V_2 }{ V_1 }} $$ $$ Q_ { 12 } =A_ { 12 } =nRT_1 \ln { \frac { V_2 }{ V_1 }} $$ and newly, taking account state equation and newly, taking account state equation $$ Q_ { 12 } =A_ { 12 } =nRT_1 \ln { \frac { P_1 }{ P_2 } \quad (VII) } $$ $$ Q_ { 12 } =A_ { 12 } =nRT_1 \ln { \frac { P_1 }{ P_2 } \quad (VII) } $$ Finally, process $ 4-1 $ is isobaric Finally, process $ 4-1 $ is isobaric $$ Q_ { 14 } = nC_p \left (T_1-T_2 \right ) \quad (VIII) $$ $$ Q_ { 14 } = nC_p \left (T_1-T_2 \right ) \quad (VIII) $$ Substituting $ (VII) $ and $ (VIII) $ into $ (III) $ Substituting $ (VII) $ and $ (VIII) $ into $ (III) $ $$ Q_c = nRT_1 \ln { \frac { P_1 }{ P_2 }} + \frac { i+2 }{ 2 } nR \left (T_1-T_2 \right ) \quad (IX) $$ $$ Q_c = nRT_1 \ln { \frac { P_1 }{ P_2 }} + \frac { i+2 }{ 2 } nR \left (T_1-T_2 \right ) \quad (IX) $$ Substituting $ (VI) $ and $ (IX) $ into $ (I) $ and developing algebraically Substituting $ (VI) $ and $ (IX) $ into $ (I) $ and developing algebraically $$ \eta = \frac { 2 \left (T_2-T_1 \right ) \ln { \frac { P_2 }{ P_1 }}}{ (i+2) \left (T_2-T_1 \right )+2T_2 \ln { \frac { P_2 }{ P_1 }}} $$ $$ \eta = \frac { 2 \left (T_2-T_1 \right ) \ln { \frac { P_2 }{ P_1 }}}{ (i+2) \left (T_2-T_1 \right )+2T_2 \ln { \frac { P_2 }{ P_1 }}} $$ Since gas is monoatomic, $ i = 3 $ , hence Since gas is monoatomic, $ i = 3 $ , hence $$ \boxed { \eta = \frac { 2 \left (T_2-T_1 \right ) \ln { \frac { P_2 }{ P_1 }}}{ 5 \left (T_2-T_1 \right )+2T_2 \ln { \frac { P_2 }{ P_1 }}}} $$ $$ \boxed { \eta = \frac { 2 \left (T_2-T_1 \right ) \ln { \frac { P_2 }{ P_1 }}}{ 5 \left (T_2-T_1 \right )+2T_2 \ln { \frac { P_2 }{ P_1 }}}} $$ </p> </p> <p style="text-align: right; font-style: italic; font-size: 14;"> <p style="text-align: right; font-style: italic; font-size: 14;"> BSc. Luis Daniel Fernández Quintana<br> BSc. Luis Daniel Fernández Quintana<br> Physics Department (FCNE)<br> Physics Department (FCNE)<br> Universidad de Oriente, Cuba<br> Universidad de Oriente, Cuba<br> </p> </p> <footer class="row container"> <footer class="row container"> <br> <br> <p> <p> <small> © <strong> Savchenko Solutions</strong> , 2023-2024 <br></small> <small> © <strong> Savchenko Solutions</strong> , 2023-2024 <br></small> </p> </p> <p> <p> <small> All rights belong to the authors. <br> Commercial use of materials - with the written permission of the authors. <br> alex@savchenkosolutions.com <br></small> <small> All rights belong to the authors. <br> Commercial use of materials - with the written permission of the authors. <br> alex@savchenkosolutions.com <br></small> </p> </p> </footer> </footer> </body> </body> </html> </html>