Light Notes
As this project is primarily concerning light it was important to look at the history behind light and its association. One of the first and oldest associations with light is found in Christianity, with God creating light in Genesis. However, it is not only Christianity that holds light so highly, many other religions also worship light, for example the Hindu festival of Divali.
Continuing on from religion, light is also held highly in the history if the Enlightenment in Greece. With new thinkers, revaluating they way in which the world worked followers of Socrates and Plato speculated that light rays leave our eyes, are reflected from objects and then returned allowing us to see.
Furthermore, legends from Ancient Rome contain many mentions of light. The story of Archimedes explains that he built an optical device to defend his hometown in Sicily against the Roman navy. A huge concave mirror was designed to reflect and focus sunlight on enemy ships and cause them to catch fire. During one battle the device supposedly burned several ships, and the others fled. It is unlikely however that they materials would have been available to cause such a device (Mythbusters).
As well as ancient history, science also explores the world of light. In the 18th Century Isaac Newton discovered the particle model. He explained that light is a stream of corpuscles or particles carrying energy. Christian Huygens, a contemporary of Newton, proposed a wave model explaining that waves require a medium and light was thought to propagate by vibrations of an invisible substance called ether.
During the 19th Century, Thomas Young, Augustin Fresnel, and others established the validity of the wave model of light beyond any doubt, causing the particle model to be forgotten about. Furthermore, during the 20th Century Albert Einstein used the particle model to explain the photoelectric effect. According to his theory massless atoms absorb bundles of light energy, these particles are now none as photons. Through these scientific experiments increasing amounts of knowledge has been discovered surrounding light and it is now understood that light has a dual nature, part particle, part wave.
Light Waves
This section takes a brief look into light waves and a few notable facts that were useful to consider for this project. Light waves can transport energy from one place to another through a medium, but the medium itself cannot be transported. A disturbance is passed along from point to point as the wave propagates. In terms of light waves, the disturbance is a changing electric and magnetic (electromagnetic) field. Once the wave has passed the environment returns to its undisturbed state. Furthermore, light waves can travel millions of miles through empty space, whereas sound waves require some medium for propagation.
It is customary to characterize materials by their index of refraction, which is the ratio of the speed of light in vacuum to the speed in the material of interest. The index of refraction is closely related to the way in which the atoms in various materials affect the electric field. The index of refraction in many materials is greater for blue light (shorter waves) than for red light (longer wavelength). This means that blue light travels slower than red light, and this is the reason white light is broken up into a spectrum of colours when passing through a glass prism. The dependence of wave speed on wavelength (or frequency) is called dispersion, so prisms made of a material with a high dispersion produce well-separated spectra of colours.
The wave theory of light is adequate to explain purely optical phenomena such as reflection, refraction, interference and polarization. As a result it is only necessary for me to consider light waves and not photons.
science museum pictures:
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