overview mirrors (temporary)

01.curriculum/01.physics-chemistry-biology/02.Niv2/04.optics/04.use-of-basic-optical-elements/02.mirror/02.new-course-overview/cheatsheet.en.md

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-new course  : overview
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+### The mirror
+
+#### What is a mirror ?
+
+##### Objective
+
+* initial : to **reflect** light, to **focus or disperse light**.
+* Ultimate : to **realize images**, alone or as part of optical instruments.
+
+##### Physical principle
+
+* uses the **phenomenon of reflection**, described by the law of reflection.
+
+##### Constitution
+
+*  Usually plane or curved (spherical for the most simple to realize,
+parabolic or elliptical) **surface, highly polished** so that its surface 
+state deviates from its theoretical form of less than $`\lambda/10`$ at each point
+of its surface ($`\lambda`$ being the wavelength in vacuum of the light to be reflected).
+To increase the reflectivity of the mirror (percentage of reflected light 
+intensity per the total of the incident light intensity), the surface is
+**most often metallized**.
+
+##### Interest in optics
+
+* **One of the most importante simple optical component** that is used *alone or 
+* combined in a series in most optical instruments* : some telephotos, 
+* reflecting telescopes.
+
+#### Why to study plane and spherical mirrors?
+
+* **Plane and spherical mirrors** are the *most technically easy to realize*, 
+so they are the *most common and cheap*.
+* In paraxial optics, the optical properties of a **plane mirror** are those 
+of a *spherical mirror of infinite radius of curvature*.
+Plane mirror, concave and convex spherical mirror
+
+
+