Update cheatsheet.en.md

01.curriculum/01.physics-chemistry-biology/03.Niv3/02.Geometrical-optics/02.geometrical-optics-foundings/01.concept-ray-of-light/02.concept-ray-of-light-overview/cheatsheet.en.md

@@ -29,14 +29,14 @@ Light rays *do not interact with each other*
 
 ##### The refraction index
 
-**Refractive Index $n$**       
-**$n \; = \; \frac{c}{v}$**
-* **c** : *speed of light in vacuum* (absolute limit)
-* **v** : *speed of light in the middle* homogeneous
+**Refractive Index $`n`$**       
+**$`n \; = \; \frac{c}{v}`$**
+* **`c`** : *speed of light in vacuum* (absolute limit)
+* **`v`** : *speed of light in the middle* homogeneous
 
-**$\Longrightarrow \: : \: n$** : physical dimension **without dimension** and **always > 1**.
+**$`\Longrightarrow \: : \: n`$** : physical dimension **without dimension** and **always > 1**.
 
-Dependency : **$n \; = \; n (\nu) \; \; \; $**, or **$ \; \; \; n \; = \; n (\lambda_0) \; \ ; \; $** *(with $\lambda_0$ wavelength in vacuum)*
+Dependency : **$`n \; = \; n (\nu) \; \; \; `$**, or **$` \; \; \; n \; = \; n (\lambda_0) \; \ ; \; `$** *(with $`\lambda_0`$ wavelength in vacuum)*
 
 <!--
 I wanted to make this important remark here, but it is not simple: with Doppler effect, medium of propagation does not move with respect to the observer ... I must think to make the warning in the main text, and a summary of all this in for example a parallel 1:
@@ -48,24 +48,24 @@ I wanted to make this important remark here, but it is not simple: with Doppler
 !! TO GO FURTHER :
 !!
 !! over the entire electromagnetic spectrum and for any medium:
-!! $n$: complex value dependent on the $\nu$ frequency of the electromagnetic wave, strong variations representative of all light / matter interaction mechanisms: $n (\nu) = \Re[n(\nu )] + \Im[n(\nu)]$ <br>
+!! $`n`$: complex value dependent on the $\nu$ frequency of the electromagnetic wave, strong variations representative of all light / matter interaction mechanisms: $`n (\nu) = \Re[n(\nu )] + \Im[n(\nu)]`$ <br>
 !!
-!! on the visible domain (where $\lambda_0$ is more used than $\nu$) and for transparent medium : <br>
-!! real value, small variations of $n$ with $\lambda_0$ ($\frac{\Delta n}{n} <1 \%$)
+!! on the visible domain (where $`\lambda_0`$ is more used than $`\nu`$) and for transparent medium : <br>
+!! real value, small variations of $`n`$ with $`\lambda_0$ ($\frac{\Delta n}{n} <1 \%`$)
 
 ##### Optical path
 
-**optical path** *$\delta$* &nbsp;&nbsp;&nbsp;&nbsp; $=$
-**euclidean length** *$s$* &nbsp;&nbsp;&nbsp; $\times$ &nbsp;&nbsp; **refractive index** *$n$*
+**optical path** *$`\delta`$* &nbsp;&nbsp;&nbsp;&nbsp; $`=`$
+**euclidean length** *$`s`$* &nbsp;&nbsp;&nbsp; $`\times`$ &nbsp;&nbsp; **refractive index** *$`n`$*
 
-* **$\Gamma$** : *path (solid line) between 2 fixed points A and B*
-* **$\mathrm{d}s_P$** : *element of infinitesimal length at point P on path $\Gamma$*
-* **$ n_P$** : *refractive index at point P*
-* **$\mathrm{d}\delta_P$** : *infinitesimal optical path at point P on path $\Gamma$*
+* **$`\Gamma`$** : *path (solid line) between 2 fixed points A and B*
+* **$`\mathrm{d}s_P`$** : *element of infinitesimal length at point P on path $`\Gamma`$*
+* **$` n_P`$** : *refractive index at point P*
+* **$`\mathrm{d}\delta_P`$** : *infinitesimal optical path at point P on path $`\Gamma`$*
 
 Optical path along a path between 2 fixed points A and B :
-**$\delta\;=\;\int_{P \in \Gamma}\mathrm{d}\delta_P\;=\;\int_{P \in \Gamma}n_P\cdot\mathrm{d}s_P$**
+**$`\delta\;=\;\int_{P \in \Gamma}\mathrm{d}\delta_P\;=\;\int_{P \in \Gamma}n_P\cdot\mathrm{d}s_P`$**
 
-* **$\delta$** $=\int_{\Gamma}n\cdot\mathrm{d}s\;=\;\int_{\Gamma}\frac{c}{v}\cdot\mathrm{d}s$ = $c\;\int_{\Gamma}\frac{\mathrm{d}s}{v}$ = *$\;c\;\tau$*
-* **$\delta$** is *proportional to the travel time*.
+* **$`\delta`$** $`=\int_{\Gamma}n\cdot\mathrm{d}s\;=\;\int_{\Gamma}\frac{c}{v}\cdot\mathrm{d}s`$ = $`c\;\int_{\Gamma}\frac{\mathrm{d}s}{v}`$ = *$`\;c\;\tau`$*
+* **$`\delta`$** is *proportional to the travel time*.