2015 Oct

Introduction to Light

October 25, 2015

Physics Tuition for Light

Light like many other forms of radiation is electromagnetic wave that are a product of an electromagnetic phenomenon. Visible light is one fraction of the wide range of electromagnetic waves that surround us. It is the limitation or the design of the eye that chooses what range of this spectrum it is capable of seeing. Electromagnetic waves can better be understood after an introduction to electricity and magnetism but will be briefly discussed here. Electromagnetic waves are simultaneously oscillating electric and magnetic fields, perpendicular to each other and travelling in the direction of the propagation of the wave. The phenomenon of light propagation can be explained using two popular theories called the ‘Corpuscular Theory of Light’ which states that light consists of particles called ‘corpuscles’ which in a more informed modern terminology can be called as photons (as taught in our A Level Physics tuition classes) and the second being the theory of wave propagation where light is considered as a wave. The property is called ‘Rectilinear Propagation of Light’. The two most important phenomenon of light namely refraction and reflection can be explained using either of these theories.

Reflection: Reflection of light occurs when light strikes a surface and bounces back. The nature in which the light bounces back speaks volumes about the nature of the surface it has struck. In the case of an ideal smooth surface, the whole beam of light bounces back at the same angle as it strikes the surface. In the case of a rough surface, the individual light rays reflect independently still adhering to what is called the law of reflection according to which the light ray reflects at the same angle as it has struck the infinitesimally small portion of the rough surface which can be approximated as a smooth portion. Reflection of light enables us to capture beautiful pictures of nature where the concept of symmetry can be observed. The idea of reflection can also be toyed around to make interesting mirrors that can create optical illusions. The eyes perceive the objects around as the light that is reflected off their surface falls on it.

Refraction: The second interesting phenomenon of light that needs some discussion is refraction of light where, light goes from one medium to another medium. One can look for “Fermat’s principle of least time’ which will be discussed in another article which explains why light travels how it travels when it is going from one medium to another. The phenomenon of refraction is used widely in correcting the vision of the eyes and in several other fields including acoustics. It is one basic principle without which half of what light does can still remain a mystery. Like any other wave light wave is also characterized by its frequency and wavelength, the number of oscillations the wave makes in one second and the length of each wave.During refraction, the frequency of the wave remains constant while the wavelength and the speed of the wave changes according to the medium in which the light wave is travelling. It would be an interesting thought experiment for the reader to wonder why it is so?

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