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M3P2
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a6d7d37e
Commit
a6d7d37e
authored
Dec 21, 2025
by
Claude Meny
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Update cheatsheet.en.md
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...
@@ -363,22 +363,22 @@ _thus revolutionizing physics._
...
@@ -363,22 +363,22 @@ _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`
$
...
@@ -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.
*$`\Longrightarrow\quad \text{div}\left(\dfrac{\partial}{\partial t}\right)= \dfrac{\partial}{\partial t}\left(\text{div}\right)`$*
.
*$`\Longrightarrow\quad \text{div}\left(\dfrac{\partial}{\partial t}\right)= \dfrac{\partial}{\partial t}\left(\text{div}\right)`$*
.
We obtain
:
We obtain
:
**$`\mathbf{\text{div}\,\overrightarrow{j} + \epsilon_0 \;\dfrac{\partial}{\partial t}\left(\text{div}\,\overrightarrow{E}\right)=0}`$**
**$`\mathbf{\text{div}\,\overrightarrow{j} + \epsilon_0 \;\dfrac{\partial}{\partial t}\left(\text{div}\,\overrightarrow{E}\right)=0}`$**
*
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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