Commit a6d7d37e authored by Claude Meny's avatar Claude Meny

Update cheatsheet.en.md

parent 8695e7cf
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...@@ -363,27 +363,27 @@ _thus revolutionizing physics._ ...@@ -363,27 +363,27 @@ _thus revolutionizing physics._
##### Study of Maxwell's equations ##### Study of Maxwell's equations
* **Let's start** with the remarkable operator combination, valid for any vector field $`\overrightarrow{U}`$, * **Let's start** with the remarkable operator combination, valid for any vector field $`\overrightarrow{U}`$,
which states: which states :
*"The divergence of the curl of a vector field is always zero."* *"The divergence of the curl of a vector field is always zero."*
<br> <br>
$`\forall \overrightarrow{X}\big(\overrightarrow{r},t\big)\;,`$*\$`\quad \mathbf{\text{div}\big(\overrightarrow{\text{curl}}\,\overrightarrow{X}\big)=0}`$*. $`\forall \overrightarrow{X}\big(\overrightarrow{r},t\big)\;,`$*\$`\quad \mathbf{\text{div}\big(\overrightarrow{\text{curl}}\,\overrightarrow{X}\big)=0}`$*.
<br> <br>
and apply it to the magnetic induction field $`\overrightarrow{B}`$: and apply it to the magnetic induction field $`\overrightarrow{B}`$ :
<br> <br>
**$`\mathbf{\text{div}\big(\overrightarrow{\text{curl}}\,\overrightarrow{B}\big)=0}`$**. **$`\mathbf{\text{div}\big(\overrightarrow{\text{curl}}\,\overrightarrow{B}\big)=0}`$**.
* The *Maxwell-Ampère law* * The *Maxwell-Ampère law*
*$`\overrightarrow{\text{curl}}\,\overrightarrow{B}=\mu_0\,\overrightarrow{j} + \mu_0\epsilon_0 \;\dfrac{\partial \overrightarrow{E}}{\partial t}`\$* $`\overrightarrow{\text{curl}}\,\overrightarrow{B}=\mu_0\,\overrightarrow{j} + \mu_0\epsilon_0 \;\dfrac{\partial \overrightarrow{E}}{\partial t}`$
allows us to write: allows us to write :
<br> <br>
**$`\mathbf{\text{div}\Big(\mu_0\,\overrightarrow{j} + \mu_0\epsilon_0 \;\dfrac{\partial \overrightarrow{E}}{\partial t}\Big)=0}`$** **$`\mathbf{\text{div}\Big(\mu_0\,\overrightarrow{j} + \mu_0\epsilon_0 \;\dfrac{\partial \overrightarrow{E}}{\partial t}\Big)=0}`$**
* Dividing both sides by $`\mu_0`$, the equation simplifies to: * Dividing both sides by $`\mu_0`$, the equation simplifies to :
<br> <br>
$`\text{div}\Big(\overrightarrow{j} + \epsilon_0 \;\dfrac{\partial \overrightarrow{E}}{\partial t}\Big)=0`$ $`\text{div}\Big(\overrightarrow{j} + \epsilon_0 \;\dfrac{\partial \overrightarrow{E}}{\partial t}\Big)=0`$
* The equation already contains $`\overrightarrow{j}`$, I seek to make $`\dens`$ appear. * The equation already contains $`\overrightarrow{j}`$, I seek to make $`\dens`$ appear.
To do this, I seek to make $`\text{div}\,\overrightarrow{j}`$ appear in order to then use the Maxwell-Gauss law. To do this, I seek to make $`\text{div}\,\overrightarrow{j}`$ appear in order to then use the Maxwell-Gauss law.
<br> <br>
$`\text{div}\,\overrightarrow{j} + \text{div}\Big(\epsilon_0 \;\dfrac{\partial \overrightarrow{E}}{\partial t}\Big)=0`$ $`\text{div}\,\overrightarrow{j} + \text{div}\Big(\epsilon_0 \;\dfrac{\partial \overrightarrow{E}}{\partial t}\Big)=0`$
...@@ -403,7 +403,7 @@ I recognize here the law of conservation of charge. ...@@ -403,7 +403,7 @@ I recognize here the law of conservation of charge.
-----------------------> ----------------------->
* In the context of *classical physics, space and time are independent*, * In the context of *classical physics, space and time are independent*,
the order of derivation with respect to a spatial variable and a time variable does not matter: the order of derivation with respect to a spatial variable and a time variable does not matter :
<br> <br>
*$`\dfrac{\partial}{\partial t}\left(\dfrac{\partial}{\partial x}\right) =\dfrac{\partial}{\partial x}\left(\dfrac{\partial}{\partial t}\right)`$* *$`\dfrac{\partial}{\partial t}\left(\dfrac{\partial}{\partial x}\right) =\dfrac{\partial}{\partial x}\left(\dfrac{\partial}{\partial t}\right)`$*
* The divergence operator consists only of partial derivatives with respect to spatial variables. * The divergence operator consists only of partial derivatives with respect to spatial variables.
...@@ -411,13 +411,13 @@ I recognize here the law of conservation of charge. ...@@ -411,13 +411,13 @@ I recognize here the law of conservation of charge.
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*$`\Longrightarrow\quad \text{div}\left(\dfrac{\partial}{\partial t}\right)= \dfrac{\partial}{\partial t}\left(\text{div}\right)`$*. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;*$`\Longrightarrow\quad \text{div}\left(\dfrac{\partial}{\partial t}\right)= \dfrac{\partial}{\partial t}\left(\text{div}\right)`$*.
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We obtain: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;We obtain :
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**$`\mathbf{\text{div}\,\overrightarrow{j} + \epsilon_0 \;\dfrac{\partial}{\partial t}\left(\text{div}\,\overrightarrow{E}\right)=0}`$** &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;**$`\mathbf{\text{div}\,\overrightarrow{j} + \epsilon_0 \;\dfrac{\partial}{\partial t}\left(\text{div}\,\overrightarrow{E}\right)=0}`$**
* Using the *Maxwell-Gauss law $`\text{div}\,\overrightarrow{E}=\dfrac{\dens}{\epsilon_0}`$* * Using the *Maxwell-Gauss law $`\text{div}\,\overrightarrow{E}=\dfrac{\dens}{\epsilon_0}`$*
<br> <br>
we obtain the **local equation of conservation of electric charge** in a time-varying regime (thus always valid): we obtain the **local equation of conservation of electric charge** in a time-varying regime (thus always valid) :
<br> <br>
**$`\mathbf{\text{div}\,\overrightarrow{j} +\dfrac{\partial \dens}{\partial t}=0}`$** **$`\mathbf{\text{div}\,\overrightarrow{j} +\dfrac{\partial \dens}{\partial t}=0}`$**
......
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