Light Waves example essay topic

Colour Physics 712 words 1. Colour physics, dispersion of sunlight into colours of the spectrum. (Sir Isaac Newton 1676) Discuss and illustrate Newton's experiments and beyond, from particle to wave theory. 2. Research, identify and illustrate how the eye sees colour, reference to light emitted, transmitted and reflected.

1. Sir Isaac Newton, held the theory that light was made up of tiny particles. Around the same period, Christiaan Huygens, believed that light was made up of waves vibrating up and down perpendicular to the direction that the light travels. Huygens theory was the successful theory of light wave motion in three dimensions. Huygen suggested that light waves peak form surfaces like the layers of an onion. In a vacuum, or other uniform medium, the light waves are spherical, and these wave surfaces advance or spread out as they travel at the speed of light.

This theory explains why light shining through a pin hole or slit will spread out rather than going in a straight line. At the time, some of the experiments conducted on light theory, both the wave theory and particle theory, had some unexplained phenomenon, Newton could not explain the phenomenon of light interference, this forced Newton's particle theory in favor of the wave theory. This difficulty was due to the unexplained phenomenon of light Polarisation - scientists were familiar with the fact that wave motion was parallel to the direction of wave travel, not perpendicular to the to the direction of wave travel as light is. In 1803, Thomas Young studied the interference of light waves by shining light through a screen with two slits equally separated, the light emerging from the two slits, spread out according to Huygen's principle. Eventually the two wave fronts will overlap with each other, if a screen was placed at the point of the overlapping waves, you would see the production of light and dark areas.

One bright afternoon, Newton darkened his room and made a hole in his window shutter, allowing just one beam of sunlight to enter the room. He then took a glass prism and placed it in the sunbeam. The result was a spectacular multi-coloured band of light just like a rainbow. The multi-coloured band of light we now know as the 'colour spectrum'. Newton believed that all the colours he saw were in the sunlight shining into his room. He thought he then should be able to combine the colours of the spectrum and make the light return to it's original state (white light).

To test this, he placed another prism upside-down in front of the first prism. He was right. The band of colours combined again into white sunlight. Newton was the first to prove that white light is made up of all the colours that we can see.

2. The human eye is the final link in the chain of colour vision. The human eye has a basic two element lens. The cornea is the front or outer element and the lens is the back or inner element. The amount of light entering the eye is controlled by the iris which lies in between the two. The light passes through a clear gel called the vitreous humor and creates an inverted image on the retina at the back of the eyeball.

The retina is the light sensitive part of the eye. Its surface is coated with millions of photoreceptor's. These photoreceptor's sense the light and pass electrical signals indicating its presence through the optic nerve to stimulate the brain. There are two types of photoreceptor's; rods and cones. The rods are sensitive to very low levels of light but are monochromatic and cannot see colour. That's why (apparently) at very low light levels, humans see things in black and white.

The retina contains three types of cones. Different light sensitive pigments within each of these three types responds to different wavelengths of light. Red cones are mostly stimulated by light in the red-yellow spectrum. Green cones are mostly stimulated by light in the yellow-green spectrum. Blue cones are mostly stimulated by light in the blue violet spectrum.

Bibliography

, web 2. html web Vision. html web harry. htm web (Video) 'Concepts in Science, Senior Physics' 4/98 web.