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Introduction

History of Light There have been six main theories of light over the past 3000 years: The tactile theory, the emission theory, the corpuscular theory, the wave theory, the electromagnetic theory and the quantum theory. The Tactile Theory This was based on the ability to touch. It stated that the eye sent out invisible probes to "feel objects". The Emission Theory This was the opposite of the tactile theory, stating that bright objects sent out beams or particles that would rebound off objects and enter the eye. It became accepted over the tactile theory by the eleventh century. The Corpuscular & Wave Theory This was put forward by Isaac Newton in 1666. ...read more.

Middle

Huygens suggested that shadows are a result of light bending round corners. Thus, he proposed that light was a wave. But this could not explain the photoelectric effect. However, there was a problem with the theory, as other waves e.g. water and sound waves needed a medium to travel. Yet, light could travel through space to reach the earth. Hooke developed a theory that space was not empty, but could not prove it. Particles do not need a medium in which to propagate, thus Newton's particle theory continued to reign until 1850. Newton explained that when light enters water from air, the velocity of the particle will increase in the water. ...read more.

Conclusion

The wave theory thus became an accepted theory of light. However, although it provided an explanation of phenomena such as interference and diffraction, it fails to explain situations like the photoelectric effect, which is the emission of electrons from the surface of solids when irradiated. The Quantum Theory Finally in 1905, Einstein explained that the energy of a light beam is not spread evenly, but concentrated in certain regions which propagate like particles. These he called 'photons'. Light apparently has a dual nature. The particle and wave theories are not conflicting but rather they are complementary. In cases involving the exchange of energy, the particle nature of light dominates the wave nature, whereas for experiments involving interference and diffraction, where light interacts with light, the wave nature dominates. Today, the quantum theory dominates the explanation of the theory of light. ...read more.

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