People began to think of light nature already in the very ancient time. Gradually through many centuries of separate observations there was a harmonious theory. At the present historical situation basic laws by which the person is guided in the activity are formulated.
Historical digression
Today each child of the advanced school age showing interest in surrounding reality knows what is light and what nature it has. Schools and colleges of laboratory are equipped with the equipment allowing to see confirmation to those laws which are formulated in textbooks. To reach such level of understanding and representation, the mankind had to pass a long and difficult way of knowledge. To break through through dogmatism and obscurantism.
Ancient Egypt considered that people around of people objects let out own image. Getting into eyes of people, radiation forms at them the corresponding image. The Ancient Greek scientist Aristotle represented a world picture differently. This is the person, his eye is a source of beams which he "feels" a subject. Today judgments of this sort raises an indulgent smile. Fundamental studying the physical nature of light began within the general development of science.
By the beginning of the eighteenth century the science accumulated the sufficient volume of knowledge and observations to formulate the basic concepts about what nature light has. The point of view of Christiaan Huygens was that radiation extends in space wavy. Famous and dear Isaac Newton came to a conclusion that light is not a wave, but a stream of the smallest particles. He called these particles corpuscles. At that time the scientific community accepted the corpuscular theory about light.
On the basis of this postulate it is easy to present what light consists of. Scientists and experimenters studied nearly two hundred years properties of light in a visible part of a range. To the middle of the 19th century in physics as to science, other ideas of what is light appeared. The law of the electromagnetic field which was formulated by the Scottish scientist James Maxwell harmoniously connected Huygens and Newton's ideas. In fact light is a wave and a particle at the same time. Took quantum of electromagnetic radiation for unit of measure of a light stream or other word – a photon.
Laws of classical optics
Basic researches of light in the nature allowed to accumulate sufficient information and to formulate basic laws which explain properties of a light stream. Among them the following phenomena appear:
- Rectilinear distribution of a beam in a homogeneous environment;
- Reflection of a beam from an opaque surface;
- Refraction of a stream on border of two non-uniform environments.
In the doctrine about light Newton explained existence of multi-colored beams with presence at them of the corresponding particles.
Effect of the law of refraction can be observed in living conditions. For this purpose the special equipment is not required. It is enough to deliver on sunny day to the sun the glass glass filled with water and to place in it a tea spoon. Upon transition from one environment to another, more dense, particles change a trajectory of the movement. As a result of change of a trajectory, the spoon in a glass is represented bent. So Isaac Newton explains this phenomenon.
Within the quantum theory this effect is explained by change of wavelength. When the ray of light gets to more dense environment, the speed of its distribution decreases. It occurs when the light stream passes from air into water. To the contrary, flow rate increases upon transition from water to air. This fundamental law is used in devices which are used to determination of density of technical liquids.
In the nature everyone can see effect of refraction of a light stream in the summer after a rain. The seven-color rainbow over the horizon results from sunlight refraction. Light passes through dense layers of the atmosphere in which collect fine water vapor. From a school course of optics it is known that white light is divided into seven components. It is easy to remember these colors – red, orange, yellow, green, blue, blue, violet.
The law of reflection is formulated still by ancient thinkers. Using several formulas, the observer can define change of the direction of a light stream after the meeting with the reflecting surface. The falling and reflected light stream are in one plane. The hade of a beam is equal to the angle of reflection. These properties of light are used in microscopes and mirror cameras.
The law of rectilinear distribution says that in a homogeneous environment visible light spreads in a straight line. Air, water, oil can be an example of homogeneous environments. If on the line of distribution of a beam to place a subject, then there will be a shadow from this subject. In the non-uniform environment the flow direction of photons changes. A part is absorbed Wednesday, a part changes a vector of the movement.
Light sources
Throughout all history of the development the mankind uses natural and artificial light sources. Natural it is accepted to carry the following sources to number:
- Sun;
- Moon and stars;
- Some representatives of flora and fauna.
Some experts refer to this category fire which is present at a fire, the furnace, a fireplace. The northern lights which are observed in the Arctic latitudes are included into the list too.
It is important to note that light nature at the listed "stars" different. When the electron in structure of atom, passes from a high orbit to low, in surrounding space the photon is allocated. This mechanism is the cornerstone of sunlight emergence. In the Sun the long time remains temperature over six thousand degrees. The stream of photons "comes off" the atoms and directs in space. About 35% of this stream get to Earth.
The moon does not let out photons. This celestial body only reflects light which got on a surface. Therefore lunar lighting does not bring heat as solar. The property of some living organisms and plants to let out quanta of light is acquired by them owing to long evolution. The firefly in darkness of night attracts to himself insects to livelihood. The person has no such abilities and for increase in comfort uses artificial lighting.
Hundred fifty years ago candles, lamps, a splinter and torches had big distribution. The population of the earth, in the majority, used one light source – naked flame. Properties of light interested engineers and scientists. Studying the wave nature of light led to important inventions. In use electric glow lamps appeared. In recent years lighting fixtures on the basis of light-emitting diodes are presented at the market.
Important properties of light
Light wave in the optical range is perceived by eyes of the person. Range of perception is small, from 370 to 790 nanometers. If the frequency of fluctuation is lower than this indicator, then ultra-violet radiation "settles" on skin in the form of suntan. Short-wave emitters are used in a sunbed for skin care during the winter period. Infrared radiation which frequency outside the upper bound, is felt as warmly. Practice of the last years confirmed advantages of infrared heaters before electric.
The person perceives the world around thanks to ability of the eyes to perceive electromagnetic waves. The retina of an eye has ability to catch photons and to betray the obtained information for processing to certain sites of a brain. This fact demonstrates that people are a part of the surrounding nature.