The wave theory of light Huygens defined light as a wave, similar to sound or mechanical waves that occur in water. On the other hand, Newton affirmed that the light was formed by material particles to which it denominated corpuscles.
Light has always aroused the interest and curiosity of the human being. In this way, since its inception one of the fundamental problems of physical It has been unveiling the mysteries of light.
Christiaan Huygens
For these reasons, throughout the history of science there have been different theories that purport to explain their true nature.
However, it was not until the end of the 17th century and the beginning of the 18th century, with the theories of Isaac Newton and Christiaan Huygens, when they began to lay the foundations for a deeper knowledge of light.
Principles of Huygens' wave theory of light
In 1678, Christiaan Huygens formulated his wave theory of light, which later, in 1690, he published in his work Treatise on light.
The Dutch physicist proposed that light was emitted in all directions as a set of waves that moved through a medium he called ether. Since the waves are not affected by gravity, it assumed the speed of the waves was reduced when they entered a denser medium.
His model proved particularly useful in explaining Snell-Descartes' law of reflection and refraction. He also satisfactorily explained the phenomenon of diffraction.
His theory was based fundamentally on two concepts:
a) The light sources emit spherical waves, similar to the waves that occur on the surface of the water. In this way, the rays of light are defined by lines whose direction is perpendicular to the surface of the wave.
b) Each point of a wave is in turn a new emitter center of secondary waves, which are emitted with the same frequency and speed that characterized the primary waves. The infinity of the secondary waves is not perceived, so that the wave resulting from these secondary waves is their envelope.
However, Huygens' wave theory was not accepted by the scientists of his time, except for a few exceptions such as Robert hooke .
The enormous prestige of Newton and the great success that reached its mechanics along with the problems to understand the concept of the ether, made that most contemporary scientists to both opted for the corpuscular theory of the English physicist.
Reflection
The reflection is an optical phenomenon that takes place when a wave strikes obliquely on a surface of separation between two media and undergoes a change of direction, being returned to the first medium together with part of the energy of the movement.
The laws of reflection are the following:
First law
The reflected ray, the incident and the normal (or perpendicular), are located in the same plane.
Second law
The value of the angle of incidence is exactly the same as that of the angle of reflection.
The principle of Huygens allows to demonstrate the laws of reflection. It is verified that when a wave reaches the separation of the media, each point becomes a new emitting source emitting secondary waves. The reflected wave front is the envelope of the secondary waves. The angle of this reflected secondary wave front is exactly the same as the incident angle.
Refraction
However, refraction is the phenomenon that occurs when a wave strikes obliquely over a gap between two media, which have a different refractive index.
When this happens, the wave penetrates and is transmitted by the second of medium together with part of the energy of the movement. The refraction happens as a consequence of the different speed with which the waves propagate in the different media.
The Huygens principle provided a convincing explanation of refraction. The points on the wavefront located at the boundary between the two media act as new sources of light propagation and thus the direction of propagation changes.
Diffraction
Diffraction is a physical phenomenon characteristic of waves (it occurs in all types of waves) that consists of the deviation of the waves when they find an obstacle in their path or go through a slit.
It should be borne in mind that diffraction occurs only when the wave is distorted by an obstacle whose dimensions are comparable to its wavelength.
The theory of Huygens explains that when the light falls on a slit all the points of its plane become secondary sources of waves emitting, as already explained previously, new waves that in this case receive the name of diffracted waves.
The unanswered questions of Huygens theory
The Huygens principle left a series of questions unanswered. His claim that each point of a wavefront was in turn a source of a new wave, did not explain why light propagates both backwards and forwards.
Equally the explanation of the concept of ether was not entirely satisfactory and was one of the reasons why his theory was initially not accepted.
Recovery of the wave model
It was not until the 19th century when the wave model was recovered. It was mainly thanks to the contributions of Thomas Young who succeeded in explaining all the phenomena of light on the basis that light is a longitudinal wave.
In particular, in 1801 he made his famous double-slit experiment. With this experiment Young tested a pattern of interference in light from a distant light source when it diffracted after passing through two slits.
Similarly, Young also explained through the wave model the scattering of white light in the different colors of the rainbow. He showed that in each medium each of the colors that make up the light has a characteristic frequency and wavelength.
In this way, thanks to this experiment he demonstrated the wave nature of light.
Interestingly, over time this experiment proved key to demonstrating the duality corpuscle wave of light, a fundamental feature of quantum mechanics.
References
- Burke, John Robert (1999). Physics: the nature of things . Mexico City: International Thomson Editors.
- "Christiaan Huygens." Encyclopedia of World Biography . 2004. Encyclopedia.com. (14 December 2012).
- Tipler, Paul Allen (1994). Physical. 3rd Edition . Barcelona: Reverté.
- David A. B. Miller Huygens's wave propagation principle corrected, Optics Letters 16, pp. 1370-2 (1991)
- Huygens-Fresnel principle (n.d.). In Wikipedia. Retrieved on April 1, 2018, from en.wikipedia.org.
- Light (n.d.). In Wikipedia. Retrieved on April 1, 2018, from en.wikipedia.org.
Young's experiment (n.d.). In Wikipedia. Retrieved on April 1, 2018, from es.wikipedia.org.