The physics of light
Light and lenses are the most common topic used to introduce the idea of electromagnetic waves and we use this idea of waves to explain reflection, diffraction and interference.
The usual approach to the physics of lenses however generally ignores the wave or photon theory of light and rather uses a simple old fashioned approach of ray diagrams and equations.
Two of the notes sheets below set out the basics of drawing ray diagrams and two explain the basics of reflection and refraction.
There is a more detailed explanation of interference on video here.
There are free videos explaining in detail how ray diagrams are drawn both for converging (convex) lenses and diverging (concave lenses) here.