Do electrons and light move at the same speed?

Light is an electromagnetic wave, and visible light is an electromagnetic wave with a wavelength of 400-700 nanometers. Electromagnetic waves less than 400 nanometers are ultraviolet rays, such as x-rays; Electromagnetic waves greater than 700 nanometers are infrared rays, such as microwaves and broadcast radio waves. The wavelength unit is nanometer,

What is light?

We have been arguing whether "light" belongs to waves or particles, and even Newton, who is famous for classical mechanics, has discussed this issue. Since then, physics has developed into quantum theory (1900) and quantum mechanics, and then Einstein published the phase theory in 1904, giving a new explanation to the definition of light: light is both a wave and a particle. In other words, there is nothing wrong with both sides who have been arguing endlessly.

Light is an electromagnetic wave and a manifestation of energy. It travels at a speed of 300,000 kilometers per second in a vacuum, and nothing can travel faster than light-some people say it can't be absolute. In black and white photography, we usually use red or green filters. Its principle is to use the filter to absorb light with different colors from its own, and convert the absorbed light energy into heat energy and release it. It is for this reason that you often feel that the filter screen is heating when you use it. For electromagnetic waves, what the human eye can recognize is called visible light, which is what we usually call "light". Light itself is invisible, and we can only feel it by looking at the light source and relying on the reflector. Some insects use ultraviolet light to identify objects, vipers use infrared light to identify objects, while dogs, cows, cats and horses can't identify colors.

Types of lamps

Light sources can be divided into three types.

The first is the light produced by thermal effect. Sunlight is a good example. Besides, candles and other items are the same. This light will change color with the change of temperature.

The second is atomic luminescence. The fluorescent substance coated on the inner wall of fluorescent tube is excited by electromagnetic wave energy to produce light, and the principle of neon lamp is the same. Atomic luminescence has its own basic color, so we need to make corresponding corrections when shooting colors.

Third, the synchrotron emits light and carries powerful energy. This is the kind of light emitted by an atomic furnace, which we hardly touch in our daily life. It is enough to remember the first two.

Impression of light

Light travels in a straight line. When it touches something, it will reflect. If it is a transparent object, it will pass through. Depending on the density of matter, there will be twists and turns. This is the principle of the lens. In addition, light still scatters when it meets translucent substances (such as soft light plates), that is, it loses parallelism and scatters in any direction. Therefore, the intensity of light will decrease in the process of propagation. On the contrary, if light is not divided, it can travel far. We know that lasers have such characteristics, and the most common example around us is searchlights, which will be discussed later. Specific shooting uses astigmatism, direct light or a mixture of the two. Knowing these differences will be of great help to taking a photo.

Direct light and reflected light

Astigmatism refers to scattered light. Think about the sunshine that shines indoors through the curtains in the afternoon, and you will have a general impression. Astigmatism can be divided into two types, one is formed by transmitted light, and the other is formed by reflected light (in actual shooting, we use a soft light plate to get astigmatism, and the reflected light is reflected by a mirror).

If the sunlight passes through the soft light board, the light will be scattered around by the soft light paper. At this time, the light in the dark part of the nearby subject is strengthened, while the light in the high place is weakened, and the photos taken will appear very soft. At this time, the main light source is the soft light board-to be exact, it should be the part of the soft light board that is irradiated by sunlight. If the whole soft light board is a square with a side length of 10 m and the illuminated part is a square with a side length of 1 m, then the size of the main light source should be within the range of 1 m.

When the model is close to the soft light board, the main light source becomes larger and the astigmatism effect will be brighter than before. In addition, the effect of using white paper and white cloth is the same. Astigmatism is a way to disturb the parallelism of light, so it is difficult to have obvious shadow parts in the astigmatism environment, and the outline of the shadow will be blurred or even invisible. However, direct light is usually used to obtain clear shadow edges.

Let's start with direct light. You can imagine that the sun shines directly on a person's face. Compared with the reflected light around, the sunshine at this time is very strong, and the difference between light and shade is quite large, giving people a clear contrast impression. Let's start with the complex object shadow and draw a straight line to the opposite point of the object that causes the shadow. After the straight line is extended, it will intersect at one place, and the light source exists at the intersection. The number of intersection points and the number of light sources should be equal. The light of the sun and the moon are parallel (it is difficult for us to prove that they are not parallel by physical means), so there will be no intersection. This phenomenon can be proved by geometry.

contrast

Contrast refers to the difference between light and dark, which is simply the difference in the amount of light between highlights and shadows. When we say that the contrast is strong, we mean that the amount of light entering the highlights and shadows is very different; Small contrast is just the opposite.

Therefore, we can know that the contrast of photos taken with astigmatism should be relatively low under the same other conditions-giving people the impression that the light is very smooth and soft, setting off a luxurious atmosphere. However, due to the lack of contrast, this photo may not appear clear enough. On the other hand, the advantage of small brightness difference is that it is helpful for color film to reproduce various colors.

Contrary to astigmatism, images taken in direct light give people a distinct feeling, and if the ratio of light to dark is moderate, it can also play a role in emphasizing the three-dimensional sense of the subject. At the same time, the edge of the image in the photo looks clearer. This kind of light is difficult to correctly show the color of the subject.

Astigmatism is more suitable for Japanese painting, especially for paintings that emphasize subtle chromatic aberration, emotion and subjectivity. Direct light is suitable for western painting, or when you want to give people an objective impression. In printing, direct light is suitable for black and white, and astigmatism is suitable for color. We will continue to launch it in the future.

The combination of telescope head and astigmatism is more suitable for Japanese painting and decorative shooting; The combination of direct light and telescope head is suitable for shooting powerful images, such as moving scenes. The combination of wide-angle lens and direct light is very objective, giving people the impression of the west; The combination of astigmatism and wide-angle lens is in the middle and the most difficult to control. There is no concept of light and shadow in oriental painting techniques.

Sometimes when you encounter physical terms, you can look them up in Modern Chinese Dictionary. If you don't understand them at all, you can look at the literal explanation first. (See page 468 of the revised edition)

Light: usually refers to the substance that shines on an object so that people can see it, such as sunlight, light, moonlight, etc. Visible light is an electromagnetic wave with a wavelength of 0.77-0.39 micron. In addition, it also includes invisible infrared light and ultraviolet light. Because light is a kind of electromagnetic wave, it is also called light wave. Generally speaking, light travels in a straight line, so it is also called light.

Knowledge of light

In a narrow sense, optics is a science about light and vision. In the early days, the word optics was only used for things related to eyes and vision. Today, optics is in a broad sense. It studies the generation, propagation, reception and display of electromagnetic radiation and its interaction with matter in a wide wavelength range from microwave, infrared, visible light, ultraviolet to X-ray.

the development history of optics

Optics is a discipline with a long history, which can be traced back to more than 2000 years ago.

At first, human beings mainly tried to answer the question "how can people see the objects around them?" Questions like this. About 400 BC (pre-Qin), China recorded the earliest optical knowledge in the world in Mo Jing. It has eight optical records, describes the definition and generation of shadow, linear propagation of light and pinhole imaging in rigorous words, and discusses the object-image relationship in plane mirror, concave spherical mirror and convex spherical mirror.

Since the Mohist Scripture, 1 1 Ibn, an Arab in the century? Hessel invented the lens; From 1590 to1early 7th century, Zhan Sen and Lipski independently invented the microscope at the same time. It was not until the first half of17th century that Snell and Descartes attributed the observation results of light reflection and refraction to the reflection law and refraction law which are widely used today.

1665, Newton experimented with sunlight and decomposed it into simple components, which formed a light distribution with colors arranged in a certain order-spectrum. It makes people come into contact with the objective and quantitative characteristics of light for the first time, and the spatial separation of monochromatic light is determined by the properties of light.

Newton also found that when a convex lens with a large radius of curvature is placed on an optical flat glass, a group of colored concentric annular stripes appear at the contact between the lens and the glass plate when it is irradiated with white light; When irradiated with a monochromatic light, a group of concentric annular stripes alternating light and dark appear, which is called Newton's ring by later generations. With this phenomenon, the corresponding monochromatic light can be quantitatively characterized by the air gap thickness of the first dark ring.

When Newton discovered these important phenomena, according to the linear propagation of light, he thought that light was a particle flow. Particles fly out of the light source and move in a uniform straight line according to the laws of mechanics. Newton used this view to explain refraction and reflection.

Huygens is an opponent of the particle theory of light, and he founded the wave theory of light. It is put forward that "light, like simultaneous light, propagates through spherical wavefront". It is also pointed out that every point reached by light vibration can be regarded as the vibration center of the secondary wave, and the envelope surface of the secondary wave is the wavefront of the propagating wave. In the whole18th century, the particle flow theory of light and the wave theory of light have been put forward, but they are not complete.

/kloc-at the beginning of the 0/9th century, wave optics was initially formed, among which Thomas? Yang satisfactorily explained the phenomenon of "film color" and double-slit interference. Fresnel supplemented Huygens' principle with Young's interference principle in 18 18, thus forming Huygens-Fresnel principle which is widely known today. It can be used to satisfactorily explain the interference and diffraction of light and the straight-line propagation of light.

In the further study, the polarization of light and the interference of polarized light are observed. In order to explain these phenomena, Fresnel assumes that light is a shear wave propagating in a continuous medium (ether). In order to explain the difference of light speed in different media, it must be assumed that the characteristics of ether in different substances are different; More complex assumptions are needed in anisotropic media. In addition, it must be given more special properties to explain that light is not longitudinal wave. Ether of this nature is unimaginable.

1846, Faraday discovered that the vibration plane of light rotates in a magnetic field; 1856, Weber found that the speed of light in vacuum is equal to the ratio of electromagnetic unit to electrostatic unit of current intensity. Their findings show that there is a certain internal relationship between optical phenomena and magnetic and electrical phenomena.

1860 or so, Maxwell pointed out that the change of electric field and magnetic field cannot be confined to a certain part of space, but propagates at a speed equal to the ratio of electromagnetic unit to electrostatic unit of current, and light is such a electromagnetic phenomena. This conclusion was confirmed by Hertz experiment in 1888.

However, this theory can't explain the essence of the electric oscillator that can produce such a high frequency of light, and it can't explain the dispersion phenomenon of light. It was not until 1896 that Lorenz founded the electronic theory that he explained the phenomena of light emission and absorption by matter and the various characteristics of light propagation in matter, including the explanation of dispersion. In Lorenz's theory, ether is an infinite and immovable medium, and its only feature is that the vibration of light has a certain propagation speed in this medium.

Lorenz theory can not give a satisfactory explanation for such an important problem as the distribution of energy by wavelength in hot blackbody radiation. Moreover, if Lorenz's concept of ether is correct, we can choose a fixed ether as the frame of reference, so that people can distinguish absolute motion. In fact, in 1887, Michelson measured the "etheric wind" with an interferometer and got a negative result, which shows that people still have a lot of one-sided understanding of the nature of light during Lorenz's electronic theory period.

1900, Planck borrowed the concept of discontinuity from the molecular structure theory of matter and put forward the quantum theory of radiation. He believes that electromagnetic waves of various frequencies, including light, can only be emitted from the vibrator with the energy of its own determined composition. This kind of energy particle is called quantum, and the quantum of light is called photon.

Quantum theory not only naturally explains the law of radiation energy distribution according to wavelength, but also puts forward the whole problem of interaction between light and matter in a brand-new way. Quantum theory not only provides a new concept to optics, but also to the whole physics, so its birth is usually regarded as the starting point of modern physics.

1905, Einstein explained the photoelectric effect with quantum theory. He made a very clear statement about photons, especially pointing out that when light interacts with matter, light also takes photons as the smallest unit.

1905 In September, the German Yearbook of Physics published Einstein's article "Electrodynamics of Moving Media". The basic principle of special relativity was put forward for the first time. It is pointed out that the application scope of classical physics, which has been dominant since Galileo and Newton's time, is limited to the case that the speed is much less than the speed of light, and his new theory can explain the characteristics of processes related to high-speed motion, completely giving up the concept of ether and satisfactorily explaining the optical phenomenon of moving objects.

In this way, at the beginning of the 20th century, on the one hand, the interference, diffraction and polarization of light and the optical phenomena of moving objects confirmed that light is electromagnetic wave; On the other hand, the quantum nature of light-particle nature, has been undoubtedly proved from the aspects of thermal radiation, photoelectric effect, light pressure and chemical action of light.

The Compton effect discovered in 1922, the Raman effect discovered in 1928, and the ultra-fine structure of atomic spectrum obtained by experiments at that time all indicate that the development of optics is closely related to quantum physics. The development history of optics shows that the two most important basic theories in modern physics, quantum mechanics and special relativity, were born and developed in the study of light.

Since then, optics has entered a new era, making it an important part of the frontier of modern physics and modern science and technology. One of the most important achievements is the discovery of atomic and molecular stimulated radiation predicted by Einstein in 19 16, and the creation of many specific technologies to produce stimulated radiation.

When studying radiation, Einstein pointed out that under certain conditions, if stimulated radiation can continue to excite other particles, causing a chain reaction and obtaining an avalanche-like amplification effect, it will eventually obtain monochromatic radiation, that is, laser. 1960, Mayman made the first visible laser from ruby; In the same year, he-ne laser was manufactured; 1962 produced a semiconductor laser; 1963 produced a tunable dye laser. Laser has been rapidly developed and widely used since its discovery in 1958 because of its good monochromaticity, high brightness and good directivity, which has caused great changes in science and technology.

Another important branch of optics is imaging optics, holography and optical information processing. This branch can be traced back to the microscopic imaging theory put forward by Abbe in 1873 and the experimental verification completed by Porter in 1906. 1935, Zelnik put forward the phase contrast observation method, and made a phase contrast microscope by Zeiss factory, for which he won the 1953 Nobel Prize in physics. 1948, dennis gabor put forward the principle of wavefront reconstruction, the predecessor of modern holography, for which dennis gabor won the 197 1 Nobel Prize in physics.

Since 1950s, people began to combine mathematics, electronic technology and communication theory with optics, and introduced the concepts of spectrum, spatial filtering, carrier wave, linear transformation and related operations into optics, which updated the classical imaging optics and formed the so-called "Brillouin optics". Coupled with the coherent light provided by laser and the holography improved by Liz and Pattner, a new subject field-optical information processing is formed. Optical fiber communication is an important achievement based on this theory, which provides a brand-new technology for information transmission and processing.

In modern optics, people pay more and more attention to the nonlinear optical phenomenon produced by intense laser. Laser spectroscopy, including laser Raman spectroscopy, high-resolution spectroscopy and picosecond ultrashort pulses, and the emergence of tunable laser technology have greatly changed the traditional spectroscopy and become an important means to deeply study the microstructure, motion law and energy conversion mechanism of substances. It provides an unprecedented technology for the study of dynamic processes in condensed matter physics, molecular biology and chemistry.

Research content of optics

We usually divide optics into geometric optics, physical optics and quantum optics.

Geometric optics is a subject that studies the propagation of light from several basic principles obtained from experiments. It uses the concept of light and the law of refraction and reflection to describe the propagation mode of light in various media, and the result is usually the approximation or limit of wave optics under certain conditions.

Physical optics is a subject that studies the phenomenon of light in the process of propagation from the fluctuation of light, so it is also called wave optics. It can conveniently study the interference, diffraction and polarization of light and the phenomenon of light propagation in anisotropic media.

Wave optics is based on Maxwell equations of classical electrodynamics. Wave optics does not discuss the relationship between dielectric constant and permeability and material structure, but focuses on explaining the performance law of light waves. Wave optics can explain the phenomenon of light propagation in scattering media and anisotropic media, and the performance of light near the interface of media; It can also explain the dispersion phenomenon and the influence of pressure, temperature, sound field, electric field and magnetic field in various media on the phenomenon of light.

quantum optics

1900, when Planck studied blackbody radiation, he boldly put forward the hypothesis that "the energy of the oscillators that make up a blackbody can't change continuously, but can only take discrete values one by one", so as to derive an empirical formula that is in line with reality.

1905, Einstein popularized Planck's quantum theory when studying photoelectric effect, and then put forward the concept of photon. He believes that light energy is not distributed on the wavefront as described by electromagnetic wave theory, but concentrated on so-called photon particles. In the photoelectric effect, when photons irradiate the metal surface, all electrons in the metal are absorbed at one time, instead of having time to accumulate energy as predicted by electromagnetic theory. Electrons use this energy to overcome the attraction of the metal surface, that is, to do work, and the rest becomes the kinetic energy after the electrons leave the metal surface.

This subject that studies the interaction between light and matter from the nature of photons is quantum optics. Its foundation is mainly quantum mechanics and quantum electrodynamics.

This phenomenon of light, both as fluctuation and particle, is the wave-particle duality of light. Later research proved irrefutably in theory and experiment that not only light has this duality, but all substances in the world, including electrons, protons, neutrons and atoms, as well as all macroscopic things, also have fluctuation characteristics related to their own mass and speed.

applied optics

Optics is composed of many branches closely related to physics; Because of its wide application, a series of branches with strong application background also belong to the optical field. For example, photometry and radiometry related to the measurement of physical quantities of electromagnetic radiation; Taking normal human eyes as receivers, this paper studies the color perception caused by electromagnetic radiation and the chromaticity measured by psychological physical quantities. And many technical optics: optical system design and optical instrument theory, optical manufacturing and optical testing, interferometry, thin film optics, fiber optics, integrated optics; There are also branches that intersect with other disciplines, such as astronomical optics, ocean optics, remote sensing optics, atmospheric optics, physiological optics, weapon optics and so on.