in the previous chapter, we talking about the ray model of light

light is a ray

we waant to focus now not on rays

but focus on the wave (the ray is derived from the wave)

the red arrows show the direction of the wave (pepindicular to the wave wave; which is a crest)

• light, like sound has a source, always
• imagine a source s which emits light
  • let’s accept that it is a wave for now, and see what kind of predictions will have.

to model light as a wave, the first person to do this was huygen (lived the same time as newton) early 600s?

he believed in the particle model of light, lighti s actually made of small particles

• he was trying to explain everything he knew about light

hyugen wanted to model light as a wave

• a few people tried it, but huygen made this observation (known as a principle now)
  • when a pave propagates in a medium, every point along a wave front behaves like a source itself
  • and like a source, emit small wave fronts?
    • something vibrating, it is light, but every point that vibrates acts like a source , which emits wavlets?
  • every point on a given wave front is like a source that emits spherical waves
  • and to find the next point look at the waves produced by the various sources