The wave theory of light It is a theory that seeks to explain the nature of light and considers this an electromagnetic wave. It was formulated in 1678 by the Dutch physicist Christian Huygens, although at the time it had little acceptance by other scientists.
Throughout its history, humanity has always had a keen interest in understanding light, and in each age, scientists and thinkers developed various theories. However, the wave theory is the one that most accurately explains the phenomena of light, such as interference, which consists of the superposition of two or more waves in a place in space..
Interference is a phenomenon that only occurs in waves, not in particles (at the macroscopic level).
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Scientific discoveries in the 19th century provided strong evidence to support the wave theory. One of them was the pattern of light and dark bands that the English physicist Thomas Young found in his famous double slit experiment. Only waves are capable of such behavior (see figure 7).
But before that light was also considered as a stream of particles that emanated from objects: it is the corpuscular theory of light proposed by Isaac Newton (1642-1727), of whom Huygens was more or less contemporary..
With his corpuscular theory, Newton was also able to satisfactorily explain everyday phenomena such as refraction and reflection. And at the beginning of the 20th century, new findings emerged in favor of this theory..
Then it is worth asking: what is finally light? The answer is in a dual nature: when propagating, light exhibits wave behavior and when interacting with matter, it does so as a particle: the photon.
Reflection and refraction of light are behaviors that light has when it passes from one medium to another. Thanks to reflection we see our reflection on polished metal surfaces and mirrors.
Refraction is observed when a pencil or a rod seems to divide in two when partially submerged in water or we simply see them through the glass of the glass.
On the other hand, light travels in a straight line, something that Christian Huygens had also observed and to explain. Huygens proposed the following:
-Light consists of a flat wave front that propagates along a straight line.
-Both reflection and refraction occur because each wavefront is equivalent to one ray of light..
-A material medium called ether is required for light to propagate, just as sound needs air to be transmitted.
Huygens believed that light was a longitudinal wave, like sound, whose behavior was much better known for the time thanks to the experiments of Robert Boyle (1627-1691). This is how he left it embodied in his work entitled Treatise of light.
Many scientists busily searched for the ether proposed by Huygens, but never found it.
And because Newton's corpuscular theory also explained reflection and refraction, it prevailed until the early 19th century, when Thomas Young carried out his famous experiment..
To explain the reflection and refraction of light, Huygens developed a geometric construction called Huygens principle:
Any point on a wavefront is, in turn, a point source that also produces secondary spherical waves.
These are spherical waves, because we assume that the medium in which they travel is homogeneous, so a light source emits rays that propagate in all directions equally. On wave fronts or surfaces, all points are in the same state of vibration.
But when the source is far enough away, an observer perceives that the light travels in a direction perpendicular to the wavefront, which is perceived as a plane because of the distance, and also travels in a straight line..
This is the case with rays from a relatively distant source, such as the Sun..
This is a prediction of the equations formulated by James Clerk Maxwell (1831-1879) during the 19th century. When the electric and magnetic fields depend on time, they are linked in such a way that one of them generates the other.
Coupled, the fields travel as an electromagnetic wave capable of propagating even in vacuum.
The electric and magnetic fields are perpendicular to each other and to the direction of propagation of the wave. Light is not a longitudinal wave, as Huygens believed, but a transverse wave.
When atoms and molecules rearrange their constituent electrons, they emit light, so it happens in our Sun. From there, light travels in the vacuum of space at a constant speed, reaches Earth and continues on its way through material media, such as air and Water.
Visible light occupies a small band of frequencies in the electromagnetic spectrum, since we only see those to which the eye is sensitive.
The wave nature of light and its rectilinear propagation are shown in:
-The phenomena of all kinds of waves, which light is equally capable of experiencing, such as polarization, interference, diffraction, reflection and refraction.
-The iridescent colors that form on thin films of soap.
-Young's experiment, in which a wave front falls on the two slits, giving rise to new wave fronts that combine (interfere) on the opposite screen. There a characteristic pattern of bright bands is formed alternating with dark bands..
-The formation of shadows, the dark areas that appear when an object comes between the light and our eyes. If the light did not propagate in a rectilinear way, it would be possible to see through opaque objects.
By possessing wave qualities, light has a myriad of applications:
The destructive interference of light in thin films - such as the aforementioned soap bubbles - is applied to make anti-reflective coatings for glasses.
It is an intense and coherent source of light, which was possible to build once the wave-particle nature of light was understood..
It is a technique in which the interference pattern of a three-dimensional object is recorded on a flat photographic plate.
Then, by lighting the plate with the appropriate light source (usually laser), the three-dimensional image of the object is reconstructed..
It is a technique that makes use of the polarization of light, a phenomenon that arises when the electromagnetic field always oscillates in the same direction..
Polarimetry is applied industrially to know the areas where the pieces experience greater mechanical stress. In this way, the design and construction materials are optimized..
Interferometry is a technique that uses the phenomenon of light interference. It is used in astronomy by combining the light from several telescopes to form a network with higher resolution.
It is applied both in radio frequency (another region of the electromagnetic spectrum that is not visible), as well as in the optical range. Another application of interferometry is in the detection of cracks and flaws in manufactured parts..
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