Notes to a video lecture on http://www.unizor.com
Light as Corpuscles
The nature of light was one of the topics of Newton's research. He experimented with light, made instruments to research the nature of light and formulated the first theory of light - corpuscular theory.
According to corpuscular theory, light is a bunch of very small particles emitted by a source of light and flying with a very high speed. When they enter our eye, we see the light as a result of bombarding of inner surface of an eye with these tiny particles of light that Newton called corpuscles.
Each light corpuscle has mass, speed, kinetic energy and trajectory, like any other material object.
Furthermore, Newton decided that there are different kinds of light corpuscles that cause our perception as different colors. He assumed that different colors of light corpuscles are due to their different sizes.
He also realized that the white color is a combination of different kinds of light corpuscles that can be separated into different individual colors. Thus, white light after going through a green glass becomes green, because a green glass separates different kinds of light corpuscles, letting through only those that are perceived by our eye as green.
According to Newton, light corpuscles are elastic, which explains perfectly their reflection from the mirror.
The effect of refraction of light, when it changes the direction going from one medium, like air, into another, like water, was explained by Newton as a result of changing the speed of propagation of light corpuscles, when they go from one medium into another.
The corpuscular theory of light was unable to explain the effect of diffraction, when the light seems bending around an edge of an obstacles or aperture.
Here is the picture formed on a screen by red light going through a small round hole.
The corpuscular theory of light was unable to explain the effect of interference, when the light going through two small holes positioned near each other forms a complex wave-like picture on the screen.
The corpuscular theory of light was unable to explain the effect of polarization, when the light consecutively going through two crystals of tourmaline changes its intensity from maximum to zero, depending on orientation of these crystals relatively to each other, when we rotate them around the axis coinciding with the direction of light.
These and some other difficulties in explanation of observed properties of light led to another theory - the wave theory of light.
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