The transverse nature of light waves. Transverse waves

And O. Frenel knew that light waves are longitudinal, that is, they are similar to the waves sound. At that time, light waves were perceived as elastic waves on the air, which fill out all the space and penetrate the inside of each body. It seemed that the waves could not be called transverse.

But nevertheless, gradually gained more and more experimental evidence and facts that could not be explained, assuming that light waves are longitudinal. After all transverse wavescould exist solely in solid bodies. But how can the body move in solid air without resistance? Ether should not slow down the movement of tel. After all, otherwise it would not be carried out.

One simple and useful experiment with a tourmaline crystal can be considered. It is transparent and has a green color.

The tourmaline crystal has this crystal to be counted for uniaxial crystals. A rectangular plate of tourmaline is taken, it is cut off so that one face is in parallel to the axis of the crystal itself. If the bunch of electrical or sunlight Direct normally on this plate, the rotation of the plate around it will not cause changes in the intensity of light, which passes through it. There is a feeling that the passing light in the tourmaline absorbed partially and acquired a light green color. Nothing more happens. But it is mistaken. A wave of light acquires new properties.

They can be detected if the beam of light will pass through the same second crystal of the tourmaline, which is located in parallel. With the same direction of the axes of two crystals, nothing curious happens, only the light beam is increasingly weakened due to the absorption, passing through the second crystal. But when the second crystal is rotated, if the first to leave motionless, an interesting phenomenon be discovered under the name "Warming of Light". In the process of increasing the angle between two data axes, the saturation of the beam of the passing light is reduced. When two axes are perpendicular to one to the other, the light cannot pass at all. It will be completely absorbed by the second crystal. How is this explained?

Crossing light waves

From the description of the facts shown earlier, it follows:

1. First, the light wave, which comes from the light source, is absolutely symmetrical in relation to the direction by which distribution occurs. At the turnover of this crystal around the passing beam of light, its intensity has not changed during the first experiment.

2. Secondly, the wave comes from the first crystal will not have axial symmetry. The intensity of passing light through another crystal depends on its turn.

Longitudinal waves are distinguished by complete symmetry relative to the direction of distribution. The fluctuations of the longitudinal waves occur along such a direction, it is oscillation and is waves. That is why explaining the experience with the rotation of the second crystal, considering the wave of the light of the longitudinal, is not possible: it is transverse waves.

You can fully explain the experience, making two assumptions:

The assumption number one refers directly to the light: light waves - transverse waves. But in falling from the light source, the beam of light waves are fluctuations in different directions, which are perpendicular to the direction by which such a wave is distributed. IN this case, considering such an assumption, we can conclude that the wave of light has at the same time being transverse. For example, waves on the aqueous surface of such symmetry do not have, because the oscillations of water particles occur exclusively in the vertical plane.

Waves of light with oscillations in various directions, which are perpendicular to the directions of distribution, are called natural. This name is justified, because in standard conditions, such waves create different sources of lighting. This assumption is explained by the results of the first experience. The rotation of the turmoline crystal does not change the saturation of the passing beam of light, because this incident wave has an axial symmetry, even though it is a transverse wave.

The second assumption refers to the crystal itself. Tourmaline has a property to skip the wave of light with oscillations that occur in a certain plane. This light is called polarized (or flat-polarized). It is different from the natural, unpolarized.

This assumption is explained by the second experience. From the first crystal of the tourmaline, a flat-polarized light (wave) is published. When crossing crystals at the angle of ninety degrees, the wave cannot pass through the second of them. If the crossing angle is another, then there will be an equal to the projection of the wave amplitude passed through the first plate in the direction of the second axis. This is what is proof of the theory that light waves are transverse waves.

Diffraction and interference of light confirms the wave nature of light. But the waves can be longitudinal and transverse. Consider the following experience.

Polarization of light

We skip the beam of light through the rectangular plate of tourmaline, one of the faces of which is parallel to the axis of the crystal. No visible changes happened. The light was only partially redeemed in the plate and acquired a greenish color.

picture

Now after put another plate after the first. If the axes of both plates are coated, nothing happens. But if the second crystal start rotating, the light will quit. When the axes are perpendicular to, there will be no light at all. It fully absorbs the second plate.

picture

We will make two outputs:

1. The wave of light is symmetrical relative to the direction of distribution.

2. After passing the first crystal, the wave ceases to have axial symmetry.

From the point of view of longitudinal waves, it will not be possible to explain it. Consequently, the light is a transverse wave. The tourmaline crystal is polaroid. It misses light waves, whose oscillations occur in the same plane. This property is well illustrated in the following figure.

picture

Crossing light waves and electromagnetic light theory

The light that is obtained after passing the polaroid is called flat-polarized light. In polarized light, oscillations occur only in the same transverse direction.

Electromagnetic theory of light originates in the works of Maxwell. In the second half of the 19th century, Maxwell proved the theoretically existence of electromagnetic waves that can be distributed even in vacuum.

And he suggested that the light is also an electromagnetic wave. The electromagnetic theory of light is based on the fact that the speed of light and the speed of propagation of electromagnetic waves coincide.

By the end of the 19th century it was finally established that light waves occur due to the movement of charged particles in atoms. With the recognition of this theory disappeared the need for a light-base ether in which light waves apply. Light waves - These are not mechanical, and electromagnetic waves.

Light wave oscillations consist of fluctuations in two vectors: vector tension and magnetic induction vector. For the direction of oscillations in light waves, it is considered to refer to the direction of fluctuations in the vector of electric field strength.

Today at the lesson we will get acquainted with the polarization of light. We study the properties of polarized light. We will get acquainted with experimental proof of movability of light waves.

The interference and diffraction phenomena leave no doubt that the propagating light has the properties of the waves. But what waves - longitudinal or transverse?

For a long time, the founders of the Sung and Frenel wave optics considered light waves longitudinal, i.e. like sound waves. At that time, light waves were considered as elastic waves on the air, filling the space and penetrating the inside of all bodies. Such waves seemed to could not be transverse, since transverse waves could only exist in a solid body. But how can the bodies move in solid ether, not meeting resistance? After all, the ether should not prevent the movement of tel. Otherwise, the law of inertia would be carried out.

However, more and more experimental facts were gradually gained, which could not be interpreted, considering light waves longitudinal.

Experiments with tourmaline

And now, consider in detail only one of the experiments, very simple and exceptionally spectacular. This experience with tourmaline crystals (transparent green color crystals).

If you send normally to such a plate a beam of light from the electrical lamp or the sun, then the rotation of the plate around the beam no change in the intensity of the light passed through it will not cause (Fig. 1.). You might think that the light was only partially absorbed in the tourmaline and acquired a greenish color. Nothing happened more. But it is not. The light wave has acquired new properties.

These new properties are detected if the beam is forced to go through the second exact same crystal of the tourmaline (Fig. 2 (a)) parallel to the first. With the same directional axes of crystals, nothing interesting is happening: just the light beam is even more weakened due to the absorption in the second crystal. But if the second crystal rotate, leaving the first fixed, then an amazing phenomenon will be discovered - the arrangement of light. As the angle increases between the axes, the light intensity decreases. And when the axes are perpendicular to each other, the light does not pass at all. It is completely absorbed by the second crystal.

Light wave with oscillations in all directions perpendicular to the direction of distribution, called natural.

The light in which the direction of the oscillations of the light vector is somehow ordered, called polarized.

Polarization of light - This is one of the fundamental properties of optical radiation (light), consisting in the inequality of various directions in the plane perpendicular to the light beam (the direction of the spread of the light wave).

Polarizers- devices allowing the opportunity to obtain polarized light.

Analyzers- Devices with which you can analyze whether the light is polarized or not.

Scheme of the polarizer and analyzer

Crossing light waves

Of the experiments described above, two facts follow:

firstlythat the light wave coming from the light source is completely symmetric about the direction of propagation (when the crystal is rotated around the beam in the first experiment, the intensity has not changed).

secondlythat the wave released from the first crystal does not have axial symmetry (depending on the rotation of the second crystal relative to the beam, the one or another intensity of the last light is obtained).

The intensity of the light, published from the first polarizer:

The intensity of the light of the last polarizer:

The intensity of the light passed through two polarizers:

Take a conclusion: 1. Light is a transverse wave. But in the incidental source, the beam of the waves is fluctuations in all sorts of areas perpendicular to the direction of wave propagation.

2. The tourmaline crystal has the ability to skip light waves with fluctuations lying in one specific plane.

Model Polarization Model Light Wave

Polaroids

Not only tourmaline crystals are able to polarize light. In the same property, for example, have so-called polaroids. Polaroidit is a thin (0.1 mm) film of herarapite crystals applied to a celluloid or glass plate. With Polaroid, you can do the same experiments as with a tourmaline crystal. The advantage of polaroids is that you can create large surfaces, polarizing lights.

The disadvantages of polaroids refers purple tintwhich they give the white light.

New concepts arose in connection with the study of electrical phenomena, but it is easier to introduce them for the first time through the mechanics. We know that two particles attract each other and that their attraction force decreases with a square of the distance. We can portray this fact in one way that we will do, although it is difficult to understand the advantages of a new method. Small circle in fig. 49 represents an attractive body, say the sun. In fact, our picture should be represented as a model in space, and not as a drawing on the plane. Then a small circle would be in the sphere of sphere representing the sun. The body we will call trial body, posted somewhere next to the sun, will be attracted to the Sun, and the force of attraction will be directed along the line connecting the centers of both bodies. Thus, the lines in our figure indicate the direction of the strength of the attraction of the Sun for various positions of the test body. The arrows on each line show that the force is directed to the Sun; This means that this force is the force of attraction. it power line fields.While it is only a name, and there is no reason to stop on it. Our drawing has one characteristic feature that we will look at later. The power lines are built in space where there is no substance. While all the power lines, in short, fieldShow only how the test body will behave, placed near the spherical body for which the field is built.

The lines in our spatial model are always perpendicular to the surface of the sphere. Since they diverge from one point, they are more densely located near the sphere and more and more disagree from each other as they remove from it. If we increase the distance from the sphere of two or three times, the density of the lines in the spatial model (but not on our figure!) Will be four or nine times less. Thus, the lines serve two goals. On the one hand, they show the direction of forces acting on the body, placed next door to the sphere of the Sun; On the other hand, the location density silest lines Shows how power changes with distance. The image of the field in the figure, correctly interpreted, characterizes the direction of force and its dependence on the distance. Of this pattern, the law of gravity can be read as well as from the description of its action with the words or as an exact and stubborn language of mathematics. it presentation of the fieldAs we call it, it may seem clear and interesting, but there is no reason to think that the introduction of it means any real progress. It would be difficult to prove its utility in the event of a burden. Maybe someone will find it useful to consider these lines not just a pattern, but something b aboutlies, and will present the real actions of the forces passing along the lines. This can be done, but then the speed of action along the power lines should be considered infinitely large. The force acting between the two bodies according to the law of Newton depends only on the distance; time is not included in consideration. For the transfer of power from one body to another no time required. But since the movement with infinite speed does not say anything to any reasonable person, inspiring an attempt to make our drawing anything b aboutriby than the model, nothing leads to anything. But we do not intend to discuss now the problem of grave. She served us only by the introduction that simplifies the explanation of similar methods of reasoning in the theory of electricity.

We will start with the discussion of the experiment, which led to serious difficulties in mechanistic views. Let we have a current current by conductor having a circle shape. In the center of this turn is a magnetic arrow. At the time of the current appears new strengthacting on the magnetic pole and perpendicular to the line connecting the wire and pole. This force caused by a charge moving around the circumference depends, as shown by the ROUland experience, from the charge rate. These experimental facts contradict habitual lookAccording to which all the forces must act through the line connecting particles, and may depend on the distance only.

The exact expression for the strength with which the current acts on the magnetic pole is very difficult; In fact, it is much more difficult to express the forces of gravity. But we can try to present her actions as clearly as we did in case of force. Our question is: what force acts on the magnetic pole, placed somewhere near the conductor, through which the current goes? It would be quite difficult to describe this force with the words. Even mathematical formula would be difficult and uncomfortable. It is much better to imagine everything we know about the action of forces, using a picture or, rather, using a spatial model with power lines. Some difficulties are caused by the fact that the magnetic pole exists only in connection with another magnetic pole, forming a dipole. However, we can always imagine yourself a magnetic dipole of such a length that it will be possible to take into account the strength acting only on the pole, which is placed near the current. The other Pole can be considered so remote that the force acting on it can not be taken into account. For definiteness, we will assume that the magnetic pole, placed near the wire, on which the current flows is positive.

The nature of the force acting on the positive magnetic pole can be seen from fig. 50. The arrows near the wire show the direction of the current from the highest potential to the lower.

All other lines - the power lines of the field of this current lying in a certain plane. If the drawing is properly made, these lines can give us an idea of \u200b\u200bboth the direction of the vector, which characterizes the effect of the current to the positive magnetic pole and the length of this vector. The power, as we know, is a vector, and to determine it, we need to know the direction of the vector and its length. We are interested in mainly the question of the direction of force acting on the pole. Our question is: how can we find on the basis of the picture, the direction of force at any point of space?

The rule of determining the direction of force for such a model is not as simple as in the previous example, where the lines of the forces were straight. To facilitate reasoning, in the following figure (Fig. 51), only one power line is drawn. The power vector lies on the tangent of the power line, as indicated in the figure. The arrow of the power vector coincides in the direction of the arrow on the power lines. Consequently, this direction in which force acts on the magnetic pole at this point is. Good drawing or or rather good model Something also tells us about the length of the power vector anywhere. This vector should be longer where the lines are arranged more densely, i.e. near the conductor, and shorter where the lines are located less tight, i.e. away from the conductor.

In this way, the power lines or, in other words, the field allows us to determine the forces acting on the magnetic pole at any point of space. While this is the only justification for careful field construction. Knowing, what aboutexpresses the field, we will consider with a deeper interest power lines related to current. These lines are the essence of the circle; They surround the conductor and lie in the plane perpendicular to the plane in which the loop is located with a current. Considering the nature of the force in the figure, we once again come to the conclusion that the force acts in the direction perpendicular to any line connecting the conductor and the pole, for the tangent of the circle is always perpendicular to its radius. All our knowledge of the action of forces we can summarize in the construction of the field. We introduce the concept of the field along with the concepts of the current and the magnetic pole in order to simply submit the current forces.

Any current is associated with magnetic field; In other words, on the magnetic pole, placed near the conductor, according to which the current flows, some strength always acts. Note in passing that this current property allows us to build a sensitive device for detecting current. Having learned once to recognize the character of the magnetic forces from the model of the field associated with the current, we will always draw the field surrounding the conductor through which the current flows to present the action of magnetic forces at any point of space. As the first example, we consider the so-called solenoid. It is a wire spiral, as shown in Fig. 52. Our task is to study with the help of experience everything you can know about the magnetic field associated with the current current by the solenoid, and combine these knowledge in the field construction. The drawing represents us the result. Curved power lines are closed; They surround the solenoid, characterizing the magnetic field of the current.

The field formed by the magnetic rod can be represented as the same path as the current field. Fig. 53 shows it. The power lines are directed from the positive pole to the negative. The power vector always lies on the tangent of the power line and is the largest near the pole, because the power lines are located the most thickly in these places. The strength vector expresses the action of a magnet on a positive magnetic pole. In this case, the magnet, and not the current is the "source" of the field.

You should carefully compare the last two pictures. In the first case, we have a magnetic field of current flowing by solenoid, in the second - the field of the magnetic rod. We will not pay attention to the solenoid and the rod, and consider only the external fields, they are created. We immediately notice that they are completely the same; In both cases, the power lines go from one end - a solenoid or rod - to another.

The idea of \u200b\u200bthe field brings its first fruit! It would be very difficult to see any pronounced similarity between the current current by the solenoid, and the magnetic rod, if it were not found in the structure of the field.

The concept of the field can now be subjected to a much more serious test. Soon we will see whether it is more than a new presentation of the current forces. We could say: let's say a minute that the field, and only it characterizes the same way all the actions determined by its source. This is only an assumption. It would mean that if the solenoid and magnet have the same field, then all their actions should also be the same. It would mean that two solenoids for which flows electricity, behave like two magnetic rods; What they attract or repel each other depending on their mutual position is completely the same as it takes place in the case of magnetic rods. It would also mean that the solenoid and the rod attract and repel each other in the same way as two rods. In short, it would mean that all the actions of the solenoid, according to which the current flows, and the actions of the corresponding magnetic rod are the same, since the field is essential, and the field in both cases has the same character. The experiment fully confirms our assumption!

How hard it would be to foresee these facts without the concept of the field! The expression for the force acting between the conductor through which the current flows and the magnetic pole is very difficult. In the case of two solenoids, we would have to explore the forces with which both currents act on each other. But if we do it with the help of the field, we immediately determine the nature of all these actions, as soon as the similarity between the solenoid field and the magnetic rod field is detected.

We have the right to believe that the field is something much more than we thought at first. The properties of the field itself are essential for the description of the phenomenon. The difference in the sources of the field is insignificant. The value of the concept of the field is found in that it leads to new experimental facts.

The field turns out to be a very useful concept. It originated as something placed between the source and the magnetic arrow in order to describe the current force. They thought about it as a "agent" of the current through which all the actions of the current were carried out. But now the agent acts both as a translator, translating laws on a simple, clear, easily understood language.

The first success of the description using the field showed that it can be convenient for consideration of all actions of currents, magnets and charges, i.e. reviewing not directly, but using the field as a translator. The field can be viewed as something always associated with the current. It exists, even if there is no magnetic pole, with which you can detect its presence. We will try to consistently follow this new guide thread.

The field of the charged conductor can be entered in almost the same way as the field or a current or magnet field. Take the simplest example again. To draw a field of positively charged sphere, we must ask a question: what kind of force act on a small positively charged trial body, placed near the source of the field, i.e. near the charged sphere? The fact that we take positively, and not a negatively charged trial body, is a simple agreement that determines how the strength lines arrows should be drawn in. This model (Fig. 54) is similar to the field of the field of gravity due to the similarity of the laws of Coulomb and Newton. The only difference between both models is that the arrows are located in opposite directions. In fact, two positive charge are repelled, and two masses are attracted. However, the field of spheres with a negative charge (Fig. 55) will be identical to the field of gravity, since a small positive test charge will attract the source of the field.

If the electrical charge, and the magnetic pole is alone, then there is no interaction between them - neither attraction, no repulsion. Expressing such a fact in the field language, we can say: the electrostatic field does not affect the magnetostatic, and vice versa. The words "static field" mean that we are talking about a field that does not change over time. Magnets and charges could always remain each other if no external force violates their condition. Electrostatic, magnetostatic and gravitational fields are different in nature. They do not mix: each retains its individuality regardless of others.

Let's return to the electrical sphere, which has so far been alone, and suppose she came into motion due to the action of some external force. The charged sphere is moving. In the field language, this expression means: field electric charge varies with time. But the movement of this charged sphere is equivalent to the current, as we already know this from the experience of Rowland. Next, each current is accompanied by a magnetic field. Thus, the chain of our conclusions is:

Charge traffic → Electrical change

Current → Magnetic field associated with current.

Therefore, we conclude:

The change in the electric field produced by the charge movement is always accompanied by a magnetic field.

Our conclusion is based on Ersted's experience, but it contains something more. It contains recognition that the connection of an electric field varying with time, with a magnetic field is very significant for our further conclusions.

Since the charge remains alone, there is only an electrostatic field. But as soon as the charge comes into motion, the magnetic field occurs. We can say more. The magnetic field caused by the traffic movement will be the stronger than the charge and the faster it moves. This is also a conclusion from Rowland's experience. Using the back of the field, we can say: the faster the electric field changes, the stronger the magnetic field accompanying it.

We will try to translate well-known facts to us from the language of the liquid theory, developed according to the old mechanistic views, to the new field of the field. Later we will see how clear our new language is instructive and comprehensively.

Relativity and mechanics

The theory of relativity with necessity arises from serious and deep contradictions in the old theory, of which it seemed there was no exit. The strength of the new theory is consistent with the simplicity with which it allows all these difficulties using only a few very convincing assumptions.

Although the theory originated from the field problem, it should cover all physical laws. The difficulty seems to appear here. The laws of the field, on the one hand, and the laws of mechanics - on the other, have a completely different character. The electromagnetic field equations are invariant with respect to Lorentz transformations, and the mechanics equations are invariant with respect to classical transformations. But the theory of relativity requires that all the laws of nature are invariant with respect to Lorentz, and not classical transformations. The latter are only a special, limit case of Lorentz transformations, when the relative speeds of both coordinate systems are very small. If so, then the classic mechanics should be changed to coordinate it with the requirement of invariance with respect to Lorentz transformations. Or, in other words, classical mechanics cannot be fair if speeds are approaching the speed of light. The transition from one coordinate system to another can be carried out only by the only way - through the transformations of Lorentz.

The classical mechanics was not difficult to change so that it does not contradict the theory of relativity, neither the material obtained by the observation and explained by the classical mechanics. Old mechanics It is valid for low speeds and forms a letter of new mechanics.

It is interesting to consider any example of a change in classical mechanics, which makes the theory of relativity. Perhaps it will lead us to some conclusions that can be confirmed or refuted by the experiment.

Suppose that the body having a certain mass moves along the line and is exposed to external force acting in the direction of movement. The power, as we know is proportional to the change in speed. Or to say clearer, it does not matter whether this body increases its speed in one second from 100 to 101 meters per second, or from 100 kilometers to 100 kilometers and one meter per second, or from 300,000 kilometers to 300,000 kilometers and one meter per second. The force required for communication with this body of any specific speed change is always the same.

Is this the situation in terms of the theory of relativity? In no way! This law is fair only for low speeds. What is the theory of relativity, the law for high speeds approaching the speed of light? If the speed is large, it is necessary to extremely big powerTo increase it. Not the same thing is at all - to increase one meter per second, a speed equal to about 100 m / s, or the speed approaching the light. The closer the speed to the speed of light, the harder it is to increase it. When the speed is equal to the speed of light, it is already impossible to increase it further. Thus, the new, which makes the theory of relativity, is not amazing. The speed of light is the upper limit for all speeds. No ultimate force, as if greater, it was, cannot cause an increase in speed over this limit. On the place of the old the law of mechanicsBinding the strength and change of speed, a more complex law appears. From our new point of view, classical mechanics are easier because almost in all observations we are dealing with speeds, significantly smaller than the speed of light.

The cowing body has a certain mass, the so-called mass of rest.We know from mechanics that every body resists changing his movement; The greater the mass, the stronger resistance, and the less weight, the weaker the resistance. But in the theory of relativity, we have something more. The body resists the change is stronger than not only in the case when there is more rest mass, but also when its speed is greater. Body whose speeds would be approaching the speed of light, would have a very strong resistance to external forces. In classical mechanics, the resistance of this body is always something unchanged, characterized only by its mass. In the theory of relativity, it depends on the mass of rest, and from speed. Resistance becomes infinitely large as the speed approaches the speed of light.

The indicated conclusions just allow us to subject to the theory of experimental verification. Are shells moving with speeds close to the speed of light, resistance to the action of external force as it predicts the theory? Since these positions of the theory of relativity are pronounced in the form of quantitative relations, we could confirm or refute the theory if we had shells moving with speeds close to the speed of light.

We really find in the nature of the shells moving with such speeds. The atoms of the radioactive substance, for example, radium, act like a battery, which shoots projectiles moving with huge speeds. Not entering the details, we can only indicate one of the most important views of modern physics and chemistry. All substance in the world is constructed from elementary particles, the number of varieties of which is small. Like this, in one city of the building is different in size, design and architecture, but on the construction of all of them, from the hut to the skyscraper, bricks are used only by very few varieties, the same in all buildings. So, all the well-known chemical elements of our material world - from the easiest hydrogen to the most severe uranium - are built from the same kind of bricks, i.e. the same kind of elementary particles. The most difficult elements are the most difficult buildings - unstable, and they disintegrate, or, as we say, they are radioactive. Some bricks, i.e., elementary particles from which radioactive atoms consist are sometimes emitted with very large speeds close to the speed of light. An atom of an element, say radium, according to our modern views, confirmed by numerous experiments, has a complex structure, and radioactive decay is one of those phenomena in which the atom is constructed from simpler bricks - elementary particles.

With the help of very witty and complex experiments, we can detect how the particles resist the action of external force. Experiments show that the resistance rendered by these particles depends on the speed, and just as it is predicted by the theory of relativity. In many other cases, where it was possible to detect the dependence of resistance from speed, complete agreement was established between the theory of relativity and the experiment. We once again see essential features. creative work In science: prediction of certain facts theory and confirmation by their experiment.

This result leads to further important generalization. The resting body has a mass, but does not have kinetic energy, i.e. the energy of movement. The moving body has a mass, and kinetic energy. It resists a change in speed stronger than the resting body. It seems that the kinetic energy of a moving body seems to increase its resistance. If two bodies have the same mass of rest, the body with greater kinetic energy resists the action of external strength stronger.

Imagine a box filled with balls; Let the box and balls rest in our coordinate system. To bring it in motion to increase its speed, some strength is required. But will this power produce the same increasing speed in the same period of time if the balls in the box will quickly move in all directions, like molecules in gas, with medium speeds close to the speed of light? Now it will be necessary aboutenergy, since the increased kinetic energy of the balls enhances the drawer resistance. Energy, in any case, kinetic energy, resists movement as well as a weighty mass. Is this true for all types of energy?

The theory of relativity, based on its basic provisions, gives a clear and convincing answer to this question, the answer is again quantitative: any energy resists a change in movement; All energy behaves like a substance; A piece of iron weighs more when he is red for hot, than when it is cold; The radiation emitted by the Sun and passing through the space contains energy and therefore has a mass; The sun and all radiating stars lose weight due to radiation. This conclusion is completely general in nature, is an important achievement of the theory of relativity and meets all the facts that were attracted to check it.

Classical physics allowed two substances - substance and energy. The first weight was weight, and the second was a nausea. In classical physics, we had two conservation laws: one - for a substance, the other - for energy. We have already set the question of whether it preserves modern physics This look at two substances and two conservation laws. The answer is: no. According to the theory of relativity, no significant differences Between mass and energy. Energy has a mass, and the mass is energy. Instead of two conservation laws, we have only one: the law of maintaining mass-energy. This a New Look turned out to be very fruitful in further development Physics.

How did this happen that the fact that the energy has a mass, and the mass is energy, so long remained unknown? Were weighing a piece of heated iron more than a piece of cold? Now we answer "yes", but before they answered "no". Pages lying between these two answers, of course, cannot hide this contradiction.

The difficulties standing here in front of us, the same order that we met and before. The change in the mass predicted by the theory of relativity is immeasurably, it cannot be detected by direct weighing even with very sensitive scales. Proof of what the energy is not a nausea can be obtained by many very convincing, but indirect paths.

The reason for this lack of direct evidence consists in a very small value of the interchange between the substance and energy. The energy in relation to the mass is similar to the impeded currency taken relative to the currency of high value. One example will make it clear. The amount of heat capable of turning 30 thousand tons of water into pairs would weigh about one gram. The energy of such a long considered weightless simply because the mass that answers her was too small.

Old energy-substance is the second victim of the theory of relativity. The first was the medium in which light waves spread.

The effect of relativity theory goes far beyond the problems of which it originated. She removes the difficulties and contradictions of the field theory; It formulates more general mechanical laws; It replaces two conservation laws one; It changes our classic absolute time concept. Its value is not limited to the sphere of physics; It forms a shared exa covering all the phenomena of nature.

Spatio-temporal continuum

"The French Revolution began in Paris on July 14, 1789." This offer has a place and time of events. To the one who hears this statement for the first time and who does not know what Paris means, it would be possible to say: this is a city on our land, located at 2 ° East longitude and 49 ° Northern latitude. Two numbers would be characterized then the place, and on July 14, 1789 - the time in which the event occurred. In physics, the exact characteristic when and where the event occurred is extremely important, much more important than in history, since these numbers form the basis of the quantitative description.

For the sake of simplicity, we only considered only the movement along the straight. Our coordinate system was a solid rod with the beginning, but without end. Save this limit. Note on the rod various points; The position of each of them can be characterized by only one number - the coordinate point. Saying that the coordinate of the point is 7.586 m, we mean that its distance from the start of the rod is 7.586 m. On the contrary, if someone sets me any number and unit of measure, I can always find a point on the rod corresponding to this number. We see that each number corresponds to a certain point on the rod, and each point corresponds to a certain number. This fact is expressed by mathematicians in the following sentence:

All points of the rod form a one-dimensional continuum.

Then there is a point, how much is close to this point of the rod. We can associate two remote points on the rod near the segments located one by one, each of which is small. Thus, the fact that these segments that bind distant points can be taken as small as small, is the characteristic of the continuum.

Take another example. Let we have a plane or if you prefer anything more specific, the surface of the rectangular table (Fig. 66). The position of the point on this table can be characterized by two numbers, and not one, as before. Two numbers essence of the distance from two perpendicular edges of the table. Not one number, and the pair of numbers corresponds to each point of the plane; Each pair of numbers corresponds to a certain point. In other words, plane is a two-dimensional continuum.Then there are points, arbitrarily close to this point of the plane. Two remote points can be bound by a curve divided into segments, arbitrarily small. Thus, the arbitrary smallness of segments sequentially stacked on a curve connecting two remote points, each of which can be determined by two numbers, again is a characteristic of a two-dimensional continuum.

One more example. Imagine that you want as a coordinate system to consider your room. This means that you want any body position to determine relative to the walls of the room. The position of the center of the lamp, if it can be described in three numbers: two of them determine the distance from two perpendicular walls, and the third is the distance from the floor or the ceiling. Each point of space corresponds three specific numbers; Each three numbers corresponds to a certain point in space (Fig. 67). This is expressed by the offer:

Our space is a three-dimensional continuum.

There are points that are very close to each specifier. And again, the arbitrary smallness of the line segments connecting remote points, each of which is represented by three numbers, there is a characteristic of a three-dimensional continuum.

But all this is hardly referred to physics. To return to physics, you need to consider the movement of material particles. To explore and predict phenomena in nature, it is necessary to consider not only the place, but also the time of physical events. Take a simple example again.

Little pebbles that take a particle falling from the tower. Suppose that the height of the tower is equal to 80 m. Since the time of Galilean, we are able to predict the coordinates of the stone during an arbitrary moment of time after the start of its fall. Below is a "schedule", approximately describing the position of the stone after 1, 2, 3 and 4 seconds.

In our "schedule" five events are registered, each of which is represented by two numbers - the time and the spatial coordinate of each event. The first event is the beginning of the movement of the stone from a height of 80 m from the ground at the time of time equal to zero. The second event is a coincidence of a stone with a marker on a rod at an altitude of 75 m from the ground. This will be marked after one second. The last event is a blow to the stone of the Earth.

Then draw two perpendicular lines; one of them, let's say horizontal, call the time abouty axis, vertical - spatial axis. We immediately see that our "schedule" can be represented by five points in Spatio-time aboutth plane (Fig. 69).

The distances of the points from the spatial axis are the coordinates of the time specified in the first column of the "schedule", and the distance from the time aboutthe axis is their spatial coordinates.

The same connection is expressed in two ways - using the "schedule" and points on the plane. One can be built from the other. The choice between these two ideas is only a taste, for in reality they are both equivalent.

We now take another step. Imagine an improved "schedule", the provisions not for each second, but, let's say, for each cell or a thousandth fraction of a second. Then we will have many points in our spatial-time aboutth plane. Finally, if the position is given for each moment or, as mathematics say, if the spatial coordinate is given as a function of time, the combination of points becomes continuous line. Therefore, our next drawing (Fig. 70) gives not fragmentary information, as before, and the complete picture of the movement of the stone.

Movement along the solid rod (tower), i.e., movement in the one-dimensional space is presented here in the form of a curve in a two-dimensional space-time aboutm continuum. Every point in our spatial-time aboutm continuum corresponds to a pair of numbers, one of which celebrates time w.yu, and another - the spatial coordinate. On the contrary, a certain point in our spatial-time aboutm continuum corresponds to some pair of numbers characterizing the event. Two neighboring points are two events that occurred in places close to each other, and at the time of time, directly next friend after another.

You could argue against our presentation method as follows: little meaning is to represent the time of segments and mechanically connect it with space, forming a two-dimensional continuum of two one-dimensional continuum. But then you would have to be as seriously protest against all charts representing, for example, a change in temperature in New York during the last summer, or against the graphs depicting a change in the cost of life over the past few years, since each of these cases is used The same method. In temperature charts, one-dimensional temperature continuum connects with one-dimensional time sm continuum in two-dimensional temperature and temporary continuum.

Let's go back to the particle falling from the 80-meter tower. Our graphic pattern of movement is a useful agreement, as it allows us to characterize the position of the particle in any arbitrary moment of time. Knowing how the particle moves, we would like to portray her movement again. You can do this in two ways.

Recall the image of particles that change their position with time in one-dimensional space. We depict movement as a number of events in a one-dimensional spatial continuum. We do not mix the time and space by applying dynamicpicture in which provisions changewith time.

But you can depict the same movement by another. We can form staticpicture, considering the curve in two-dimensional space-time aboutm continuum. Now the movement is seen as something specified, existing in two-dimensional space-time aboutm continuum, and not as something, changing in a one-dimensional spatial continuum.

Both of these pictures are completely equal, and the preference of one of them before the other there is only a matter of agreement and taste.

The fact that it is said about two pictures of movement is not related to the theory of relativity. Both representations can be used with the same right, although the classical theory rather preferred a dynamic picture of the description of the movement as what happens in space, a static picture describing it in space-time. But the theory of relativity changed this look. She clearly chose a static picture and found in this representation of the movement as it exists in space-time, a more convenient and more objective picture of reality. We must still answer the question why these two paintings are equivalent from the point of view of classical physics and are not equivalent in terms of the theory of relativity. The answer will be clear if we again consider the two coordinate systems moving straight and evenly relative to each other.

According to classical physics, observers in both systems moving straight and evenly relative to each other will find various spatial coordinates for the same event, but the same time w.by coordinate. Thus, in our example, the strike of the land of the Earth is characterized in our choice of the time coordinate system aboutth coordinate 4 and spatial coordinate 0. According to classical mechanics, observers moving straight and evenly relative to the selected coordinate system, they will detect that the stone will reach the Earth later after four seconds after the start of the fall. But each of the observers relates the distance to its coordinate system, and they will, generally speaking, bind various spatial coordinates with the event of collision, although time buti will coordinate the same for all other observers moving straight and evenly relative to each other. Classical physics knows only the "absolute" time, current equally for all observers. For each coordinate system, the two-dimensional continuum can be broken into two one-dimensional continuum - time and space. Thanks to the "absolute" character of the time, the transition from "Static" to the "dynamic" picture of the movement has an objective meaning in classical physics.

But we have already made sure that classical transformations cannot be applied in physics in the general case. From a practical point of view, they are still suitable for low speeds, but are not suitable for the substantiation of fundamental physical issues.

According to the theory of relativity, the moment of collision of stone with the ground will not be the same for all observers. And time buti, and the spatial coordinate will be different in two different coordinate systems, and the change of time aboutthe coordinates will be very noticeable if the relative speed of the systems is approaching the speed of light. Two-dimensional continuum cannot be broken into two one-dimensional continuum, as in classical physics. We cannot consider space and time separately when defining spatial-time sx coordinates in another coordinate system. The separation of a two-dimensional continuum into two one-dimensional is in terms of the theory of relativity by an arbitrary process that does not have an objective meaning.

All that we just said is not difficult to summarize for the case of movement, not limited to the straight line. In fact, to describe events in nature, do not apply not two, but four numbers. The physical space, comprehended through objects and their movements, has three dimensions, and the positions of objects are characterized by three numbers. The moment of events is the fourth. Each event corresponds to four specific numbers; In some four numbers, a specific event corresponds to a certain event. Therefore, the world of events forms four-dimensional continuum.There is nothing mystical, and the last sentence is equally fair both for classical physics, and for the theory of relativity. And again the difference is detected only when two coordinate systems are treated, moving relative to each other. Let the room move, and the observers inside and outside it determine the spatial-time se coordinates of the same events. Supporter of classical physics breaks four-dimensional continuum on three-dimensional space and one-dimensional time aboutin continuum. The old physicist cares only about the transformation of space, as the time for it is absolutely. It finds the splitting of the four-dimensional global continuum into space and time natural and comfortable. But from the point of view of the theory of relativity, the time, as well as the space, changes during the transition from one coordinate system to another; In this case, Lorentz transformations express the transformation properties of four-dimensional spatial-time aboutcontinuum - our four-dimensional world of events.

The world of events can be described dynamically using a picture varying in time and sketched against the background of three-dimensional space. But it can also be described by a static picture pounced on the background of four-dimensional space-time aboutcontinuum. From the point of view of classical physics, both paintings, dynamic and static, equivalent. But from the point of view of the theory of relativity, the static picture is more convenient and more objective.

Even in the theory of relativity, we can still use a dynamic picture, if we prefer it. But we must remember that this division for a while and space does not have an objective point, as time is no longer "absolute". Then we will still use the "dynamic", and not the "static" language, but we will always take into account its limitations.

General theory of relativity

It remains to find out another moment. Not yet resolved one of the most fundamental questions: is there an inertial system? We learned something about the laws of nature, their invariance towards Lorentz transformations and their justice in all inertial systems moving straight and evenly relative to each other. We have laws, but do not know that the "body of reference" to which they should be attributed.

In order to know more about these difficulties, talk to the physicist standing in the position of classical physics, and ask him some simple questions.

What is an inertial system?

This is a coordinate system in which the laws of mechanics are just. The body that external forces does not act, moves in such a system straight and evenly. This property allows us to consequently distinguish an inertial coordinate system from any other.

But what does that do not work on the body external power?

It simply means that the body moves straight and evenly in the inertial coordinate system.

Here you could once again put the question: "What is an inertial coordinate system?" But because there is little hope of getting an answer other than the above, we will try to achieve specific information by changing the question.

Is the system that is rigidly associated with land, inertial?

No, because the laws of mechanics are not strictly fair on Earth due to its rotation. The coordinate system is rigidly associated with the Sun, can be considered inertial when solving many problems, but when we are talking about rotation of the Sun.We conclude again that the coordinate system is not considered strictly inertial.

Then exactly is your inertial coordinate system and how should I choose the state of its movement?

This is only a useful fiction, and I have no idea how to implement it. If only I could isolate from all material bodies and free from all external influences, then my coordinate system would be inertial.

But what do you mean by speaking about the coordinate system free from all external influences?

I mean that the coordinate system is inertial. We returned to our initial question! Our conversation reveals serious difficulty in classical physics. We have laws, but do not know what the point of reference, to which they should be attributed, and all our physical construction turns out to be erected in the sand.

We can approach the same difficulty from another point of view. We will try to imagine that in the whole universe there is only one body that makes our coordinate system. This body begins to rotate. According to classical mechanics, physical laws for the rotating body are different from laws for the infrared body. If the Inertia principle is fair in one case, it is not fair. But all this sounds very doubtful. Is it possible to consider the movement of only one body in the whole universe? Under the movement of the body, we always understand the change in its position relative to another body. Therefore, to talk about the movement of a single body - it means to contradict common sense. Classical mechanics And common sense will differ greatly at this point. Newton's recipe is such: if the inertia principle is valid, the coordinate system is either resting or moving straight and evenly. If the principle of inertia does not have strength, the body is not in a straight and uniform movement. Thus, our conclusion about the movement or rest depends on whether or not all physical laws on this coordinate system are applicable.

Take two bodies, such as the Sun and Earth. The movement we observe again relative.It can be described using the coordinate system related either with the Earth or with the Sun. From this point of view, the great achievement of Copernicus is to transfer the coordinate system from the ground in the sun. But since the movement relative and you can apply any reference body, it turns out that there is no reason to prefer one coordinate system different.

Physics interferes again and changes our generally accepted point of view. The coordinate system associated with the Sun has a greater similarity with an inertial system than the system associated with the Earth. Physical laws are preferable to apply in the Copernicus system than in the Ptolemy system. The greatness of the opening of the Copernicus can be highly appreciated only from a physical point of view. Physics shows that in order to describe the movement of the planets, the coordinate system, rigidly associated with the Sun, has huge benefits.

There is no absolute rectilinear and uniform movement in classical physics. If two coordinate systems move straight and evenly relative to each other, then there is no reason to say: "This system is resting, and the other moves." But if both coordinate systems are in an indiscriminate and uneven movement relative to each other, then there is a complete reason to say: "This body moves, and the other is resting (or moving straight and evenly)." The absolute movement has a completely definite meaning here. In this place between common sense and classical physics there is a wide abyss. Mentioned difficulties relating to the inertial system, as well as difficulties relating to the absolute movement, are closely related. The absolute movement becomes possible only due to the idea of \u200b\u200ban inertial system for which the laws of nature are just.

It may seem that there would be no way out of these difficulties, in which no physical theory can avoid them. The source lies in the fact that the laws of nature are valid only for a special class of coordinate systems, namely for inertial. The ability to resolve these difficulties depends on the answer to the next question. Can we formulate physical laws in such a way that they are valid for all coordinate systems, not only for systems moving straight and evenly, but also for systems moving completely arbitrarily in relation to each other? If this can be done, then our difficulties will be resolved. Then we will be able to apply the laws of nature in any coordinate system. The struggle between the views of Ptolemy and Copernicus, so cruel in early days Science would have become completely meaningless. Any coordinate system could be applied with the same basis. Two sentences - "The Sun is resting, and the Earth moves" and "The Sun is moving, and the Earth rests" - they would simply mean two different agreements on two different coordinate systems.

Could we build real relativistic physics, fair in all coordinate systems, physics in which there would be no absolute, but only a relative movement? It really turns out to be possible!

We have at least one, although very weak, indicating how to build new physics. Indeed, relativistic physics should be used in all coordinate systems, and therefore, in a special case - in the inertial system. We already know the laws for this inertial coordinate system. New general laws, fair for all coordinate systems, should in a special case of an inertial system to come down to old, well-known laws.

The problem of formulating physical laws for any coordinate system was allowed so-called common theory of relativity; Previous theory applied only to inertial systems is called special theory of relativity.These two theories cannot, of course, contradict each other, as we should always include the laws of the special theory of relativity established earlier in general laws for the non-inertial system. But if earlier an inertial coordinate system was the only one for which physical laws were formulated, now it will represent a special limit, since any coordinate systems moving arbitrarily relative to each other.

Such is the program of the general theory of relativity. But, outlining the way as it was created, we must be even less specific than it has so far. New difficulties arising in the process of developing science are forced our theory becoming more and more abstract. We are waiting for another number of surprises. But our constant ultimate goal is all the best and better understanding of reality. New links are added to the logical chain that connects the theory and observation. To clear the path leading from the theory to the experiment, from unnecessary and artificial assumptions to cover an increasingly extensive area of \u200b\u200bfacts, we must make the chain and longer and longer. The easier and fundamentally our assumptions become, the more difficult the mathematical instrument of our reasoning; The path from the theory to observation becomes longer, thinner and more difficult. Although it sounds paradoxically, but we can say: modern physics is easier than old physics, and therefore it seems more difficult and confusing. The simplest our picture of the outside world and the more facts it covers, the stronger it reflects in our minds the harmony of the universe.

Our new idea is simple: to build physics, just for all coordinate systems. The implementation of this idea brings a formal complication and forces us to use mathematical methodsother than those still used in physics. We will show here only the relationship between the implementation of this program and two fundamental problems - and geometry.

Interrupt continuity

We are revealed by the map of the city of New York and the surrounding area. We ask: what points on this map can be achieved by train? After reviewing these items in the railway schedule, we celebrate them on the map. Then we change the question and ask: what items can be achieved by car? If we draw on a line map, representing all the roads starting in New York, then any item lying on these roads can practically be achieved by car. In both cases, we have a number of points. In the first case, they are distant from each other and are different railway stations, and in the second they are the essence of the point along the highways. The next our question is about the distance to each of these points from New York or, for greater accuracy, from a certain place in this city. In the first case, certain numbers correspond to the points on the map. These numbers change irregularly, but always to the final magnitude, jump. We say: distances from New York to seats, which can be achieved by train, change only differently.However, the distance to the places that can be achieved by car, they can change as much as you can change, they can change continuously.Distance changes can be made arbitrarily small in case of traveling by car, not by train.

Products of coalfish can be changed in a continuous manner. The amount of coal produced can be increased or reduced arbitrarily small portions. But the number of working chickens can only be changed. It would be a pure nonsense to say: "Since yesterday, the number of employees has increased by 3.783."

The man whom was asked about the number of money in his pocket, can not be called any, how much is a small amount, but only a value containing only two decimal signs. The amount of money may vary only by jumps, intermittently. In America, the least possible change, or, as we call it, the "elementary quantum" of American money, there is one cent. An elementary quantum of English money is one farthing, standing only half of the American elementary quantum. Here we have an example of two elementary quanta, whose value can be compared with each other. The ratio of their magnitudes has a certain meaning, since the cost of one of them is twice the cost of another.

We can say: some quantities can change continuously, others can change only completely, portions that can no longer be reduced. These indivisible portions are called elementary quantamithese values.

We can weigh huge quantities Sand and consider it a lot of continuous, although his grainy structure is obvious. But if the sand became very precious, and the used scales are very sensitive, we would have to recognize the fact that the sand mass always varies on the magnitude of the multiple mass of one the smallest particles. The mass of this smallest particle would be our elementary quantum. From this example, we see how the discontinuous nature of the value, until then, considered continuous, is found due to an increase in the accuracy of our measurements.

If we had to characterize the basic ideas of quantum theory in one phrase, we could say: it should be assumed that some physical quantities previously considered continuous consist of elementary quanta.

The area of \u200b\u200bfacts covered by quantum theory is extremely large. These facts are open due to the high development of the technique of the modern experiment. Since we can not show either to describe even the main experiments, we will often have to give them the results of dogmatically. Our goal is to explain only the fundamental, basic ideas.

Elementary quanta substance and electricity

In the painting of the structure of a substance drawn by kinetic theory, all elements are built of molecules. Take the simplest example The easiest chemical element - hydrogen. We have seen how the study of the Brownian movement led to the determination of the mass of the hydrogen molecule. It is equal

0,000,000,000,000,000,000,000 003 3 g

This means that the mass is interrupted. The mass of any portion of hydrogen may vary only by an integer number of smallest portions, each of which corresponds to the mass of one hydrogen molecule. But chemical processes showed that hydrogen molecule can be broken into two parts or, in other words, that the hydrogen molecule consists of two atoms. In the chemical process, the role of elementary quantum plays an atom, not a molecule. Making the above number two, we find a mass of the hydrogen atom; It is equal to approximately

0,000,000,000,000,000,000,000 001 7

Mass is the magnitude of the intermittent. But, of course, we should not worry about it with the usual definition of body weight. Even the most sensitive scales are far from achieving such a degree of accuracy that would detect a terminating change in body weight.

Terminology of wave theory

Uniform light has a certain wavelength. The wavelength of the red end of the spectrum is twice as much wavelength of purple end.

Terminology of quantum theory

Uniform light consists of photons of certain energy. Photon energy for the red end of the spectrum twice the energy of a photon of purple end.

Litetura

Mala Gіrnich Encyclopedia. In 3 tons / ab. V. S. Bіletsky. - Donetsk: Donbas, 2004. - ISBN 966-7804-14-3..

http://znaimo.com.ua.

Casatkin A. S. Bases of Elektrotechniki. M: Visitor School, 1986.

Beltsonov L. A. Theoretical bases of the electroplating. Elektrichni Cola. M: Vice school, 1978.

slovari.yandex.ru/dict/BSE/article/00061/97100.htm.

Sivukhin D.V. Fili course Fіziki - M. T. III. Elektrick

The evolution of physics. Development of ideas from initial concepts to the theory of relativity and quanta

Albert Einstein, Leopold Infeld ( per. from English S. G. Suvorov)

The purpose of the lesson

Form the concept of "natural and polarized light" from schoolchildren; become acquainted with experimental proof of transverse light waves; explore the properties of polarized light, show analogy between the polarization of mechanical, electromagnetic and light waves; Report examples of using polaroids.

The lesson on the polarization of light is the final in the topic "Wave Optics". In this regard, the lesson using computer simulation can be constructed as a generalizing repetition lesson or part of the lesson to decide for solving problems on the topics of the Light Interference, "Light Diffraction". We offer a lesson model, which is studied new Material on the topic "Polarization of Light", and then consolidation of the studied material on computer model. At this lesson, it is easy to combine a real demonstration with computer simulation, as polaroids can be given to children in the hands and show the arrangement of light when you turn one of the polaroids.

Homework: § 74, Task No. 1104, 1105.

Explanation of the new material

The interference and diffraction phenomena leave no doubt that the propagating light has the properties of the waves. But what waves - longitudinal or transverse?

For a long time, the founders of the Sung and Fresnel wave optics considered light waves longitudinal, that is, similar sound waves. At that time, light waves were considered as elastic waves on the air, filling the space and penetrating the inside of all bodies. Such waves seemed to could not be transverse, since transverse waves could only exist in a solid body. But how can the bodies move in solid ether, not meeting resistance? After all, the ether should not prevent the movement of tel. Otherwise, the law of inertia would be carried out.

However, more and more experimental facts were gradually gained, which could not be interpreted, considering light waves longitudinal.

Experiments with tourmaline

Consider in detail only one of the experiments, very simple and spectacular. This experience with tourmaline crystals (transparent green color crystals).

Demonstrate the student to clean the light when turning two polaroids. The tourmaline crystal has a symmetry axis and belongs to the number of so-called uniaxial crystals. Take the rectangular plate of the tourmaline carved in such a way that one of its faces is parallel to the axis of the crystal. If you send normally to such a plate a beam of light from the electrical lamp or the sun, then the rotation of the plate around the beam no change in the intensity of the light passed through it will not cause (see Fig.). You might think that the light was only partially absorbed in the tourmaline and acquired a greenish color. Nothing happened more. But it is not. The light wave has acquired new properties.

These new properties are detected if the beam is forced to go through the second exact same crystal of the tourmaline (see Fig. A), parallel to the first. With the same directional axes of crystals, nothing interesting is happening: just the light beam is even more weakened due to the absorption in the second crystal. But if the second crystal is rotated, leaving the first fixed (Fig. B), then an amazing phenomenon will be discovered - the arrangement of light. As the angle increases between the axes, the light intensity decreases. And when the axes are perpendicular to each other, the light does not pass at all (Fig. B). It is completely absorbed by the second crystal. How can this be explained?

Crossing light waves

From the experiments described above, two fact follows: firstly, the light wave coming from the light source is completely symmetric about the direction of propagation (when the crystal is rotated around the beam in the first experiment, the intensity has not changed) and, secondly, that the wave released from The first crystal does not have axial symmetry (depending on the rotation of the second crystal relative to the ray, one or another intensity of the last light is obtained).

Longitudinal waves have full symmetry in relation to the direction of distribution (oscillations occur along this direction, and it is the axis of wave symmetry). Therefore, to explain the experience with the rotation of the second plate, considering the light wave of the longitudinal, is impossible.

A complete explanation of experience can be obtained by making two assumptions.

The first assumption refers to the very light. Light is a transverse wave. But in an incidental source, the beam of waves is fluctuations in all sorts of areas perpendicular to the direction of propagation of waves (see Fig.).

Demonstrate that natural light contains oscillations in all planes.

According to this assumption, the light wave has axial symmetry, being in the same time transverse. Waves, for example, do not possess such symmetry on the surface of water, since the oscillations of water particles occur only in the vertical plane.

Light wave with oscillations in all directions perpendicular to the direction of propagation is called natural. This name is justified, since in conventional conditions Sources of light create just such a wave. This assumption explains the result of the first experience. The rotation of the tourmaline crystal does not change the intensity of the last light, since the incident wave has axial symmetry (despite the fact that it is transverse).

The second assumption that needs to be done belongs to the crystal. The tourmaline crystal has the ability to skip light waves with oscillations lying in one specific plane (P flare in the figure).

On the computer model "Law of Malyus"

Demonstrate that the tourmaline crystal allocates only one plane of light oscillations. Turning the polarizer, and then the analyzer, it can be shown that the intensity of the passing light changes from the maximum value to zero. To clean the light, the angle between the axes of polaroids should be 90 °. If the axis of polaroids is parallel, then the second polaroid passes the entire light that has passed through the first.

This light is called polarized, or, more precisely, flat-polarized, unlike natural light that can also be called unpolarized. This assumption fully explains the results of the second experience. From the first crystal there is a plane-liarized wave. With crossed crystals (angle between the axes of 90 °), it does not pass through the second crystal. If the axis of the crystals make up a certain angle, different from 90 °, then fluctuations are undergoing, the amplitude of which is equal to the projection of the wave amplitude passed through the first crystal to the direction of the axis of the second crystal.

So, the turmaline crystal converts natural light into a flat-polarized.

Mechanical model of experiments with turmaline

It is easy to build a simple visual mechanical model of the phenomenon under consideration. You can create a transverse wave in the rubber cord so that the oscillations quickly change their direction in space. This is an analogue of a natural light wave. Miss now cord through narrow wooden drawer (See Fig.). From the oscillations of all kinds of areas, the box "highlights" the oscillations in one specific plane. Therefore, a polarized wave comes from the box.

If there is still exactly the same box on its path, but turned relative to the first 90 °, then the oscillations are not passing through it. The wave is fully quenched.

If there is a mechanical polarization model in the office, it is possible to demonstrate it. If there is no such model, you can illustrate this model by fragments of the videos of the polarization.

Polaroids

Not only tourmaline crystals are able to polarize light. In the same property, for example, have so-called polaroids. Polaroid is a thin (0.1 mm) herarapite crystal film applied to a celluloid or glass plate. With Polaroid, you can do the same experiments as with a tourmaline crystal. The advantage of polaroids is that you can create large surfaces, polarizing lights. The lack of polaroids includes a purple shade, which they give the white light.

Direct experiments have proven that the light wave is transverse. In the polarized light wave of oscillations occur in a strictly defined direction.

In conclusion, it is possible to consider the use of polarization in the technique and illustrate this material by fragments of the videofilm "Polarization".