What is visible light? Write various views on it.

(N/A) The portion of the electromagnetic spectrum with wavelengths ranging from $4000 \ \mathring{A}$ to $8000 \ \mathring{A}$ is known as visible light. Light itself is invisible,but it allows us to see objects.
Various views on the nature of light are as follows:
$(1)$ Corpuscular model of light (Newton's particle theory of light):
- The corpuscular theory was proposed by Descartes in $1637$. It derived Snell's law and explained the laws of reflection and refraction at the interface of two media.
- The model predicted that if a light ray bends towards the normal during refraction,its speed must be greater in the second medium. Thus,it suggested that the speed of light is lower in a rarer medium and higher in a denser medium.
- This theory is famously associated with Isaac Newton,who considered light to be composed of tiny particles called corpuscles.
$(2)$ Huygens' wave theory:
- In $1678$,Christiaan Huygens proposed the wave theory of light.
- This theory successfully explained reflection and refraction. It predicted that if a wave bends towards the normal during refraction,its speed would be less in the second medium. This contradicted the prediction of the corpuscular model.
- In $1850$,Foucault experimentally proved that the speed of light in water is less than in air,which supported the wave theory over the corpuscular model.