Lesson 40 Optics

Light is a wavelength disturbance of the electromagnetic field that propogates at a definite speed. Light has properties similar to those of all waves, waves can propogate outward from a single point of disturbance. Waves from carefully coordinated arrays of point sources can add up to form wave fronts called plane waves. Plane waves can be made to spread out again because waves bend around corners. When wave fronts encounter one another, they can produce stronger and weaker waves.

Galileo not only developed one of the first telescopes, but used it most practically. Galileo also developed the compound microscope.

Lenses of glasses, telescopes, and microscopes are based off the principle of refraction. Refraction occurs when light is bent as it travels through a medium. Manufacturers of glasses, telescopes, and microscopes develop convex lenses that refract light to a single point.

A glass prism not only bends or refracts a beam of light, but separates white light into the colors of the visible light spectrum. This is known as dispersion.

Newton theorized that reflection and refraction can be explained by the gravitational attraction between matter, however, light was composed of waves rather than particles.

Electromagnetic waves are always transverse and travel at the speed of light, and can have different frequencies and wavelengths that create the visible light spectrum. The visible light spectrum is composed of waves with lengths between 400 and 700 nanometers.

When electric charges with lines of force are set into vibration oscillating electric charges create waves that propogate along the lines of force at the speed of light. These waves become closer and closer in proximity and become wave fronts, as they become flatter farther away from the source and develop into plane waves. An electric charge is the source of outward radiation in the electric field. Thus light travels in waves.

Light has the property of waves interference and can either be constructive or destructive. If waves are in step they reinforce each other and are contructive. If waves are out of step they cancel each other and are destructive.

When light waves encounter electric charges the oscillating electric field makes the charge oscillate which creates a new outward travelling wave.

In metals, where electrons move freely, light can be reflected where the angle of incidence is equal to the angle of reflection.

Glasses function because the speed of light is slower in the glass than in the air. This causes light to refract and concentrate towards the center of the lens on the retina.