Prisme réflecteur
Good binoculars use prisms rather than mirrors, because a prism reflects essentially all the light instead of most of it. This simulation traces a ray into a right-angled prism and shows it turning through 90° or 180° by total internal reflection.
Comment utiliser cette simulation
- Choose a 90° or 180° deviating prism arrangement
- Change the glass refractive index and see the critical angle move
- Adjust the entry point of the incoming ray
Ce qu’il faut observer
- Light reflects completely at the sloping face with none escaping
- Lowering the refractive index eventually raises the critical angle past 45°, and the prism leaks
- Two internal reflections invert the image, which is how binoculars right the view
La physique derrière
Inside the glass, a ray meeting the sloping face at 45° exceeds the critical angle of about 42° for a glass–air boundary, so no light escapes and all of it reflects. Because total internal reflection loses nothing to transmission, prisms outperform metal mirrors, which always absorb a few percent at each bounce.