Light is ... The nature of light. Laws of light

Any kind of optical radiation is considered light. In other words, these are electromagnetic waves, the length of which is in the range of units of nanometers.

General Definitions

From the point of view of optics, light is electromagnetic radiation, which is perceived by the eye of a person. For the unit of change, it is customary to take the site in a vacuum of 750 THz. This is the short-wave boundary of the spectrum. Its length is 400 nm. As for the wide-wave boundary, a unit of measurement is taken at 760 nm, that is, 390 THz.

In physics, light is viewed as a set of directed particles called photons. The speed of distribution of waves in a vacuum is constant. Photons have a certain momentum, energy, zero mass. In a broader sense, light is visible ultraviolet radiation. Also, waves can be infrared. From the point of view of ontology, light is the beginning of being. This is confirmed by philosophers and religious scholars. In geography, this term is commonly used to refer to individual areas of the planet. Light itself is a social concept. Nevertheless, in science it has specific properties, features and laws.

Nature and light sources

Electromagnetic radiation is created during the interaction of charged particles. The optimum condition for this is heat, which has a continuous spectrum. The maximum radiation depends on the temperature of the source. An excellent example of the process is the Sun. Its radiation is close to those of an absolutely black body. The nature of light on the Sun is determined by the temperature of heating up to 6000 K. At the same time about 40% of the radiation is within sight. The maximum of the power spectrum is located near 550 nm.

Light sources can also be:

1. Electronic shells of molecules and atoms during the transition from one level to another. Such processes allow us to achieve a linear spectrum. An example are LEDs and gas-discharge lamps.
2. Cherenkov radiation, which is formed by the motion of charged particles with a phase velocity of light.
3. Photon deceleration processes. As a result, synchrotron or cyclotron radiation is produced.

The nature of light can also be associated with luminescence. This applies to both artificial sources and organic ones. Example: chemiluminescence, scintillation, phosphorescence, etc.

In turn, the light sources are divided into groups with respect to temperature indicators: A, B, C, D65. The most complex spectrum is observed in an absolutely black body.

Characteristics of light

The human eye subjectively perceives electromagnetic radiation as a color. So, the light can give out white, yellow, red, green overflows. This is only a visual sensation, which is related to the frequency of radiation, whether it is spectral or monochromatic in composition. It is proved that photons can propagate even in a vacuum. In the absence of matter, the flow velocity is 300,000 km / s. This discovery was made back in the early 1970s.

At the boundary of the medium, the stream of light undergoes either reflection or refraction. During the spread, it dissipates through the substance. It can be said that the optical indices of the medium are characterized by a refractive index equal to the ratio of the velocities in vacuum and absorption. In isotropic substances, the propagation of the stream does not depend on the direction. Here the refractive index is represented by a scalar quantity determined by the coordinates and time. In an anisotropic medium, the photon is manifested in the form of a tensor.

In addition, the light is polarized and not. In the first case, the main value of the definition is the wave vector. If the stream is not polarized, then it consists of a set of particles directed to random sides.

The most important characteristic of light is its intensity. It is determined by such photometric quantities as power and energy.

Basic properties of light

Photons can not only interact with each other, but also have a direction. As a result of contact with an extraneous medium, the stream experiences reflection and refraction. These are the two fundamental properties of light. With reflection, everything is more or less clear: it depends on the density of matter and the angle of incidence of the rays. However, with refraction the situation is much more complicated.

To begin with, you can consider a simple example: if you drop a straw into the water, then from the side it appears curved and shortened. This is the refraction of light, which occurs at the boundary of the liquid medium and air. This process is determined by the direction of the distribution of the rays during the passage through the boundary of matter. When the light flux touches the boundary between media, the wavelength of its wave changes significantly. Nevertheless, the propagation frequency remains the same. If the ray is not orthogonal with respect to the boundary, then the wavelength and its direction will undergo a change.

Artificial refraction of light is often used for research purposes (microscopes, lenses, magnifiers). These sources of change in wave characteristics include glasses.

Classification of light

At present, artificial and natural light are distinguished. Each of these species is determined by the characteristic source of radiation.

Natural light is a collection of charged particles with a chaotic and rapidly changing direction. Such an electromagnetic field is caused by variable oscillation of the stresses. The natural sources include hot bodies, the sun, polarized gases.

Artificial light can be of the following types:

1. Local. It is used in the workplace, on the kitchen area, walls, etc. Such lighting plays an important role in interior design.
2. Common. This uniform illumination of the whole area. The sources are chandeliers, floor lamps.
3. Combined. Mixture of the first and second species to achieve an ideal room illumination.
4. Emergency. It is extremely useful when you turn off the lights. Power is most often from batteries.

sunlight

Today it is the main source of energy on Earth. It is no exaggeration to say that sunlight affects all important matters. This is a quantitative constant, which determines the energy.

In the upper layers of the earth's atmosphere, about 50% of infrared radiation and 10% of ultraviolet radiation are contained. Therefore, the quantitative component of visible light is only 40%.

Solar energy is used in synthetic and natural processes. This is photosynthesis, and the conversion of chemical forms, and heating, and much more. Thanks to the sun, mankind can use electricity. In turn, streams of light can be direct and scattered if they pass through clouds.

The Three Main Laws

Since ancient times, scientists have been studying geometric optics. To date, the following laws of light are fundamental:

1. Law of distribution. It says that in a homogeneous optical medium, light will be distributed rectilinearly.
2. The law of refraction. A ray of light incident on the boundary of two media, and its projection from the point of intersection lie on one plane. This also applies to the perpendicular dropped to the point of contact. In this case, the ratio of the sines of the angles of incidence and refraction will be constant.
3. Law of reflection. The ray of light that falls on the boundary of the medium and its projection lie on the same plane. The angles of reflection and fall are equal.

Perception of light

The world around a person is visible due to the ability of his eyes to interact with electromagnetic radiation. Light is perceived by retinal receptors, which can be captured and reacted to the spectral range of charged particles.

A person has 2 types of sensitive eye cells: cones and rods. The first cause the mechanism of vision in the daytime with a high level of illumination. The rods are more sensitive to radiation. They allow a person to see at night.

The visual shades of light are determined by the wavelength and its direction.