HUYGENS WAVE THEORY OF LIGHT - PHYSICAL - 2024

The wave theory of light Huygens defined light as a wave, similar to the sound or mechanical waves produced in the water. On the other hand, Newton claimed that light was made up of material particles which he called corpuscles.

Light has always aroused human interest and curiosity. In this way, since its inception one of the fundamental problems of physics has been to unveil the mysteries of light.

Christiaan huygens

For these reasons, throughout the history of science there have been different theories that tried to explain its true nature.

However, it was not until the late seventeenth and early eighteenth centuries, with the theories of Isaac Newton and Christiaan Huygens, that the foundations for a deeper understanding of light began to be laid.

Principles of Huygens wave theory of light

In 1678, Christiaan Huygens formulated his wave theory of light, which he later published in 1690 in his Treatise on light.

The Dutch physicist proposed that light was emitted in all directions as a set of waves that traveled through a medium that he called ether. Since waves are not affected by gravity, he assumed the speed of the waves would decrease when they entered a denser medium.

His model was particularly helpful in explaining the Snell-Descartes law of reflection and refraction. It also satisfactorily explained the phenomenon of diffraction.

His theory was fundamentally based on two concepts:

a) Light sources emit spherical-shaped waves, similar to the waves that occur on the surface of water. In this way, the light rays 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 emitting center for secondary waves, which are emitted with the same frequency and speed that characterized the primary waves. The infinity of secondary waves is not perceived, so the wave resulting from these secondary waves is their envelope.

However, Huygens' wave theory was not accepted by scientists of his time, with few exceptions such as Robert Hooke's.

The enormous prestige of Newton and the great success that his mechanics achieved, together with the problems to understand the concept of the ether, made most of the contemporary scientists to both opt for the corpuscular theory of the English physicist.

Reflection

Reflection is an optical phenomenon that takes place when a wave is obliquely incident on a separation surface 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 as follows:

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.

Huygens' principle allows us to demonstrate the laws of reflection. It is found that when a wave reaches the separation of the media, each point becomes a new emitter focus emitting secondary waves. The reflected wavefront 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 takes place when a wave obliquely impinges on a gap between two media, which have different refractive indexes.

When this happens, the wave penetrates and is transmitted for a half second along with part of the energy of the movement. Refraction occurs as a consequence of the different speed with which the waves propagate in the different media.

A typical example of the phenomenon of refraction can be observed when an object (for example, a pencil or a ballpoint pen) is partially inserted into a glass of water.

Huygens' principle provided a compelling explanation for refraction. The points on the wave front 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 characteristic physical phenomenon of waves (it occurs in all types of waves) that consists of the deflection of waves when they encounter an obstacle in their path or pass 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.

Huygens' theory explains that when light falls on a slit, all the points in its plane become secondary sources of waves, emitting, as previously explained, new waves, which in this case are called diffracted waves.

The unanswered questions of Huygens theory

Huygens's principle left a series of questions unanswered. His claim that each point on a wavefront was in turn a source of a new wave failed to explain why light propagates both backward and forward.

Likewise, the explanation of the concept of ether was not entirely satisfactory and was one of the reasons why his theory was not initially accepted.

Recovery of the wave model

It was not until the 19th century that the wave model was recovered. It was mainly thanks to the contributions of Thomas Young who managed to explain all the phenomena of light on the basis that light is a longitudinal wave.

Specifically, in 1801 he carried out his famous double slit experiment. With this experiment, Young verified an interference pattern in light from a distant light source when it diffracted after passing through two slits.

In the same way, Young also explained by means of 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 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 corpuscle wave duality of light, a fundamental characteristic of quantum mechanics.

References

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2. "Christiaan Huygens." Encyclopedia of World Biography. 2004. Encyclopedia.com. (December 14, 2012).
3. Tipler, Paul Allen (1994). Physical. 3rd Edition. Barcelona: I reversed.
4. David AB Miller Huygens's wave propagation principle corrected, Optics Letters 16, pp. 1370-2 (1991)
5. Huygens – Fresnel principle (nd). In Wikipedia. Retrieved on April 1, 2018, from en.wikipedia.org.
6. Light (nd). In Wikipedia. Retrieved on April 1, 2018, from en.wikipedia.org.

Young's experiment (nd). On Wikipedia. Retrieved on April 1, 2018, from es.wikipedia.org.