Second Isaac Newton (1643-1727), light was composed of corpuscular particles, small spheres that collided with surfaces and suffered reflection and refraction. Years later with the studies of electromagnetism and the contributions of James Maxwell (1831-1879), light was defined as a electromagnetic wave, that is, a combination of electric fields and magnetic variables that propagate in space.
When a quantity is found only in integer multiples of an elementary quantity (called quantum), it is said to be quantized. In the 20th century, Albert Einstein (1879-1955) proposed that electromagnetic radiation should be quantized and the elementary quantity that defined light was the photon.
Wave or particle?
Anyway, is light a type of wave or a tangle of particles that propagate in space? The answer to that question is intriguing. Light is both a wave and a particle. THE wave-particle duality of light shows us this double behavior.
Light undergoes phenomena such as refraction, dispersal and polarization
, characteristic of the waves. However, to understand the photoelectric effect, for example, it must be considered that it is composed of particles called photons.photons
You photons are the particles that make up light and can be defined as small “packets” that carry the energy contained in electromagnetic radiation. According to Einstein, a photon must have a fixed amount of energy, defined by the following equation:
In this equation, AND is the energy belonging to the photon, f is the frequency of electromagnetic radiation (Hz) and H and the Planck's constant, which has a value of 6.63 x 10 – 34J.s or 4.14 x 10 – 15 eV.s.
According to this definition, the minimum amount of energy that an electromagnetic wave must have corresponds to the product h.f, and any energy value for an electromagnetic radiation must be an integer multiple of that product.
photon mass
According to Einstein, the energy of an object depends on a relationship between its mass and its speed.
In the equation above, AND is the energy accumulated by a body, m is the mass of the element and ç is the speed of light. By equating this equation to the one that defines the energy of a photon, we can define its mass. This element has no mass at rest, that is, it will not have mass if it is at rest.
Photons have momentum
When a photon interacts with matter, energy transfer occurs, so it can be defined that this element has linear motion (p), also called amount of movement.
In the equation above, P is the amount of movement of the photon, H is Planck's constant (6.63 x 10 – 34J.s or 4.14 x 10 – 15 eV.s) and λ is the wavelength of electromagnetic radiation.
Photons in everyday life
Some everyday technologies work from interaction with photons. At lamps that light up on their own are connected to a device called a photovoltaic cell. This equipment releases electrons when receiving the photons that make up sunlight. That electric current, when passing through a coil, it generates a magnetic field that maintains the circuit open. During the night, with the lack of sunlight, the flow of electrons is interrupted, causing the circuit to close and turn on the lamp.
Another application is the device called a photometer. Widely used by photographers, this equipment is a light meter that determines the intensity of a light source through photon reception.
By Joab Silas
Graduated in Physics
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/fisica/o-que-sao-fotons.htm
