What is light? This question has interested mankind in all ages, but only in the 20th century AD, much was clarified regarding the nature of this phenomenon. This article will focus on the corpuscular theory of light, its advantages and disadvantages.
From ancient philosophers to Christian Huygens and Isaac Newton
Some evidence that has survived to our time says that people began to be interested in the nature of light in ancient Egypt and ancient Greece. At first it was believed that objects emit images of themselves. The latter, getting into the human eye, create the impression of the visibility of objects.
Then, during the formation of philosophical thought in Greece, a new theory of Aristotle appeared, who believed that each person emits some rays from the eyes, thanks to which he can "feel" objects.
The Middle Ages did not bring any clarity to the issue under consideration, new achievements came only with the Renaissance and the revolution in science. In particular, in the second half of the 17th century, two completely opposite theories appeared, which sought toexplain the phenomena associated with light. We are talking about the wave theory of Christian Huygens and the corpuscular theory of Isaac Newton.
Despite some successes of the wave theory, it still had a number of important shortcomings:
- believed that light propagated in the ether, which was never discovered by anyone;
- the transverse nature of the waves meant that the ether had to be a solid medium.
Taking into account these shortcomings, and also given the huge authority of Newton at that time, the theory of particles-corpuscles was accepted unanimously in the circle of scientists.
The essence of the corpuscular theory of light
Newton's idea is as simple as possible: if all the bodies and processes around us are described by the laws of classical mechanics, in which bodies of finite mass participate, then light is also small particles or corpuscles. They move in space at a certain speed, if they meet an obstacle, they are reflected from it. The latter, for example, explains the existence of a shadow on an object. These ideas about light lasted until the beginning of the 19th century, that is, about 150 years.
It is interesting to note that Lomonosov used the Newtonian corpuscular theory in the middle of the 18th century to explain the behavior of gases, which is described in his work "Elements of Mathematical Chemistry". Lomonosov considered gas to be composed of corpuscle particles.
What did Newtonian theory explain?
The outlined ideas about light madea huge step in understanding its nature. Newton's theory of corpuscles was able to explain the following phenomena:
- Rectilinear propagation of light in a homogeneous medium. Indeed, if no external forces act on a moving corpuscle of light, then its state is successfully described by the first Newtonian law of classical mechanics.
- The phenomenon of reflection. Hitting the interface between two media, the corpuscle experiences an absolutely elastic collision, as a result of which its modulus of momentum is preserved, and it itself is reflected at an angle equal to the angle of incidence.
- The phenomenon of refraction. Newton believed that penetrating into a denser medium from a less dense one (for example, from air into water), the corpuscle accelerates due to the attraction of the molecules of the dense medium. This acceleration leads to a change in its trajectory closer to the normal, that is, a refraction effect is observed.
- The existence of flowers. The creator of the theory believed that each observed color corresponds to its own "color" corpuscle.
Problems of the stated theory and return to Huygens' idea
They began to emerge when new light-related effects were discovered. The main ones are diffraction (deviation from the rectilinear propagation of light when a beam passes through a slit) and interference (the phenomenon of Newton's rings). With the discovery of these properties of light, physicists in the 19th century began to recall the work of Huygens.
In the same 19th century, Faraday and Lenz investigated the properties of alternating electric (magnetic) fields, andMaxwell carried out the corresponding calculations. As a result, it was proved that light is an electromagnetic transverse wave, which does not require ether for its existence, since the fields that form it generate each other in the process of propagation.
New discoveries related to light and the idea of Max Planck
It would seem that Newton's corpuscular theory has already been completely buried, but at the beginning of the 20th century new results appear: it turns out that light can "pull out" electrons from matter and exert pressure on bodies when it falls on them. These phenomena, to which an incomprehensible spectrum of a blackbody was added, the wave theory turned out to be powerless to explain.
The solution was found by Max Planck. He suggested that light interacts with the atoms of matter in the form of small portions, which he called photons. The energy of a photon can be determined by the formula:
E=hv.
Where v - photon frequency, h - Planck's constant. Max Planck, thanks to this idea of light, laid the foundation for the development of quantum mechanics.
Using Planck's idea, Albert Einstein explains the phenomenon of the photoelectric effect in 1905, Niels Bohr - in 1912 gives a rationale for atomic emission and absorption spectra, and Compton - in 1922 discovers the effect that now bears his name. In addition, the theory of relativity developed by Einstein explained the role of gravity in the deviation from the linear propagation of a beam of light.
Thus, the work of these scientists of the early 20th century revived Newton's ideas aboutlight in the 17th century.
Corpuscular-wave theory of light
What is light? Is it a particle or a wave? During its propagation, whether in a medium or in airless space, light exhibits the properties of a wave. When its interactions with matter are considered, it behaves like a material particle. Therefore, at present, with respect to light, it is customary to talk about the dualism of its properties, which are described within the framework of the corpuscular-wave theory.
A particle of light - a photon has neither charge nor mass at rest. Its main characteristic is energy (or frequency, which is the same thing, if you pay attention to the expression above). A photon is a quantum mechanical object, like any elementary particle (electron, proton, neutron), therefore it has a momentum, as if it were a particle, but it cannot be localized (determine the exact coordinates), as if it were a wave.
