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| <h2>Solutions of Savchenko Physics Textbook</h2> |
| <h2>Solutions of Savchenko Physics Textbook</h2> |
| <p class="author"> |
| <p class="author"> |
| Aliaksandr Melnichenka <br/> |
| Aliaksandr Melnichenka <br/> |
| October 2023 |
| October 2023 |
| </p> |
| </p> |
| </header> |
| </header> |
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| <main> |
| <h3 id="back-link"><a href="../">$\leftarrow$Back</a></h3> |
| <article> |
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| <h3 id="back-link"><a href="../">$\leftarrow$Back</a></h3> |
| <h3> Statement </h3> |
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| <p> |
| <h4>Statement</h4> |
| $6.5.2$ |
| <p> |
| Two electroconductor pistons of cross section $S$ form a plane capacitor in a tube of an isolating material which contains air at atmospheric pressure $P_0$. How changes the distance between pistons if charges of different signs $\pm Q$ are applied to them? The system is good heat conductor and there is no friction. |
| $6.5.2$ |
| </p> |
| Two electroconductor pistons of cross section $S$ form a plane capacitor in a tube of an isolating material which contains air at atmospheric pressure $P_0$. How changes the distance between pistons if charges of different signs $\pm Q$ are applied to them? The system is good heat conductor and there is no friction. |
| <center> |
| </p> |
| <figure> |
| <center> |
| <img src="statement.png" |
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| loading="lazy" alt="6.5.2" width="200" /> |
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| <figcaption> |
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| For problem 6.5.2 |
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| </figcaption> |
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| </figure> |
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| </center> |
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| <h3>Solution</h3> |
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| <p> |
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| Let's consider the following figure |
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| </p> |
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| <center> |
| <figure> |
| <figure> |
| <img src="statement.png" |
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| loading="lazy" alt="6.5.2" width="200" /> |
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| <figcaption> |
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| For problem 6.5.2 |
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| </figcaption> |
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| </figure> |
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| </center> |
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| <h4>Solution</h4> |
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| <p class="TxtSolutions"> |
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| Let's consider the following figure |
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| </p> |
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| <center> |
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| <figure> |
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| <img src="draw.png" |
| <img src="draw.png" |
| loading="lazy" alt="6.5.2" width="450" /> |
| loading="lazy" alt="6.5.2" width="450" /> |
| <figcaption> |
| <figcaption> |
| Forces over pistons |
| Forces over pistons |
| </figcaption> |
| </figcaption> |
| </figure> |
| </figure> |
| </center> |
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| <p class="TxtSolutions"> |
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| Applying Newton Second Law over one of the piston, considering the pistons are massless, |
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| </p> |
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| <center> |
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| $F_p = F_{p0} + F_e$ |
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| </center> |
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| <p class="TxtSolutions"> |
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| where $F_p$, $F_{p0}$ and $F_e$ are forces due to enclosed air between pistons, due to atmospheric pressure and due to electric field, respectively. |
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| </p> |
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| <center> |
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| $P = P_0 + \frac{F_e}{S} \;(1)$ |
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| </center> |
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| <p class="TxtSolutions"> |
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| The electric force $F_e$ is defined from the electric field generated by a charged plate that is $E = \frac{\sigma}{2\varepsilon_0}=\frac{Q}{2\varepsilon_0 S}$, so |
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| </p> |
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| <center> |
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| $F_e = Q E =\frac{Q^2}{2\varepsilon_0 S} \;(2)$ |
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| </center> |
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| <p class="TxtSolutions"> |
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| Putting $(2)$ into $(1)$ |
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| </p> |
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| <center> |
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| $P = P_0 + \frac{Q^2}{2\varepsilon_0 S} \;(3)$ |
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| </center> |
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| <p class="TxtSolutions"> |
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| Taking account that the system is good heat conductor, we can suppose that thermal equilibrium is instantaneously established or that the container acts as a thermos, keeping the temperature unchanged.Then, applying Boyle-Mariotte law |
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| </p> |
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| <center> |
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| $P_0 S L = P S l$ |
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| </center> |
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| <center> |
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| $\frac{L}{l} = \frac{P}{P_0} \;(4)$ |
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| </center> |
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| <p class="TxtSolutions"> |
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| Substituting $(3)$ into $(4)$ |
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| </p> |
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| <center> |
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| $\boxed{\frac{L}{l} = 1 + \frac{Q^2}{2P_0\varepsilon_0 S^2}}$ |
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| </center> |
| </center> |
| <p class="TxtSolutions" style="text-align: center; font-style: italic; font-size: 14;"> |
| <p> |
| BSc. Luis Daniel Fernández Quintana<br> |
| Applying Newton Second Law over one of the piston, considering the pistons are massless, |
| Physics Department (FCNE)<br> |
| $$F_p = F_{p0} + F_e$$ |
| Universidad de Oriente, Cuba<br> |
| where $F_p$, $F_{p0}$ and $F_e$ are forces due to enclosed air between pistons, due to atmospheric pressure and due to electric field, respectively. |
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| $$P = P_0 + \frac{F_e}{S} \;(1)$$ |
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| The electric force $F_e$ is defined from the electric field generated by a charged plate that is $E = \frac{\sigma}{2\varepsilon_0}=\frac{Q}{2\varepsilon_0 S}$, so |
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| $$F_e = Q E =\frac{Q^2}{2\varepsilon_0 S} \;(2)$$ |
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| Putting $(2)$ into $(1)$ |
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| $$P = P_0 + \frac{Q^2}{2\varepsilon_0 S} \;(3)$$ |
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| Taking account that the system is good heat conductor, we can suppose that thermal equilibrium is instantaneously established or that the container acts as a thermos, keeping the temperature unchanged.Then, applying Boyle-Mariotte law |
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| $$P_0 S L = P S l$$ |
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| $$\frac{L}{l} = \frac{P}{P_0} \;(4)$$ |
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| Substituting $(3)$ into $(4)$ |
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| $$\boxed{\frac{L}{l} = 1 + \frac{Q^2}{2P_0\varepsilon_0 S^2}}$$ |
| </p> |
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| BSc. Luis Daniel Fernández Quintana<br> |
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| Physics Department (FCNE)<br> |
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| Universidad de Oriente, Cuba<br> |
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