Experiments in optics experiments and experiments in physics on the topic. Experiments in physics

Russian light

In 1876 in London at the exhibition of precise physical instrumentsditch Russian inventor Pavel Nikolaevich I blochkov demonstrated to the visitors an extraordinary electricity a candle. Similar in shape to the usual stearic, NS that candle burned with a blinding light. In the same year, "Yablochkov's candles" appeared on the streets of Paris. Placed in white matte balls, they gave a bright pleasant light. Va short time a wonderful candle of Russian inventors forfought universal recognition. "Yablochkov's candles" were illuminated the best hotels, streets and parks of the largest cities in Europe, Accustomed to the dim light of candles and kerosene llamas people of the last century admired "Yablochkov's candles". New light was called "Russian light", "northern light". Newspapers forWestern European countries wrote: “Light comes to us from the north - from Russia ”,“ Russia is the birthplace of light ”.

Didactic material

Spreading light

As we know, one of the types of heat transfer is radiation. With radiation, the transfer of energy from one body to another can be carried out even in a vacuum. There are several types of radiation, one of which is visible light.

The illuminated bodies gradually heat up. This means that light is really radiation.

Light phenomena are studied by a branch of physics called optics. The word "optics" in Greek means "visible", because light is a visible form of radiation.

The study of light phenomena is extremely important for humans. After all, more than ninety percent of information we receive thanks to vision, that is, the ability to perceive light sensations.

Bodies that emit light are called light sources - natural or artificial.

Examples of natural light sources are the sun and other stars, lightning, and glowing insects and plants. Artificial light sources are a candle, a lamp, a burner and many others.

Any light source consumes energy when emitting.

The sun emits light thanks to the energy from the nuclear reactions taking place in its depths.

A kerosene lamp converts the energy released during the combustion of kerosene into light.

Light reflection

A person sees a light source when a beam emanating from this source hits the eye. If the body is not a source, then the eye can perceive rays from any source reflected by this body, that is, falling on the surface of this body and changing the direction of further propagation. A body that reflects rays becomes a source of reflected light.

The rays falling on the surface of the body change the direction of further propagation. When reflected, light returns to the same medium from which it fell onto the surface of the body. A body that reflects rays becomes a source of reflected light.

When we hear this word "reflection", first of all, we are reminded of a mirror. In everyday life, flat mirrors are most often used. Using a flat mirror, a simple experiment can be carried out to establish the law by which light is reflected. We place the illuminator on a sheet of paper lying on the table so that a thin beam of light lies in the plane of the table. In this case, the light beam will slide over the surface of the sheet of paper, and we will be able to see it.

Place a flat mirror vertically in the path of a thin light beam. A beam of light will bounce off it. You can make sure that the reflected beam, like the one falling on the mirror, slides along the paper in the plane of the table. Mark with a pencil on a sheet of paper the relative position of both light beams and the mirror. As a result, we will obtain a scheme of the experiment carried out. The angle between the incident beam and the perpendicular restored to the reflecting surface at the point of incidence is commonly called the angle of incidence in optics. The angle between the same perpendicular and the reflected beam is the angle of reflection. The results of the experiment are as follows:

1. The incident beam, the reflected beam and the perpendicular to the reflecting surface, reconstructed at the point of incidence, lie in the same plane.
2. The angle of incidence is equal to the angle of reflection. These two conclusions represent the law of reflection.

Looking at a flat mirror, we see images of objects that are located in front of it. These images exactly repeat the appearance of objects. It seems that these twin objects are located behind the surface of the mirror.

Consider an image of a point source in a flat mirror. To do this, we will randomly draw several rays from the source, construct the corresponding reflected rays and then complete the extensions of the reflected rays beyond the plane of the mirror. All the extensions of the rays will intersect behind the plane of the mirror at one point: this point is the image of the source.

Since in the image it is not the rays themselves that converge, but only their extensions, in reality there is no image at this point: it only seems to us that rays emanate from this point. Such an image is usually called imaginary.

Refraction of light

When the light reaches the separation of two media, part of it is reflected, while the other part passes through the border, refracting at the same time, that is, changing the direction of further propagation.

A coin immersed in water seems to us to be larger than when it is just lying on the table. A pencil or a spoon, placed in a glass of water, seems to us broken: the part in the water seems to be raised and slightly enlarged. These and many other optical phenomena are explained by the refraction of light.

Refraction of light is due to the fact that in different media, light propagates at different speeds.

The speed of propagation of light in a given medium characterizes the optical density of a given medium: the higher the speed of light in a given medium, the lower its optical density.

How will the angle of refraction change during the transition of light from air to water and during the transition from water to air? Experiments show that when passing from air to water, the angle of refraction turns out to be less than the angle of incidence. And vice versa: when passing from water to air, the angle of refraction turns out to be greater than the angle of incidence.

From experiments on light refraction, two facts became obvious: 1. The incident ray, the refracted ray and the perpendicular to the interface between the two media, reconstructed at the point of incidence, lie in the same plane.

1. When going from an optically denser medium to an optically less dense medium, the angle of refraction is greater than the angle of incidence.When going from an optically less dense medium to an optically denser one, the angle of refraction is less than the angle of incidence.

An interesting phenomenon can be observed if the angle of incidence is gradually increased as light passes into an optically less dense medium. The angle of refraction in this case is known to be greater than the angle of incidence, and with an increase in the angle of incidence, the angle of refraction will also increase. At a certain value of the angle of incidence, the angle of refraction will be equal to 90 °.

We will gradually increase the angle of incidence as light passes into an optically less dense medium. As the angle of incidence increases, the angle of refraction will also increase. When the angle of refraction becomes equal to ninety degrees, the refracted ray does not pass into the second medium from the first, but slides in the plane of the interface between these two media.

This phenomenon is called total internal reflection, and the angle of incidence at which it occurs is the limiting angle of total internal reflection.

The phenomenon of total internal reflection is widely used in technology. The use of flexible optical fibers is based on this phenomenon, through which light rays pass, being repeatedly reflected from the walls.

The light does not leave the fiber due to total internal reflection. A simpler optical device that uses total internal reflection is a reversible prism: it flips the image by swapping the rays entering it.

Image in lenses

A lens whose thickness is small compared to the radii of the spheres forming the surface of this lens is called thin. In what follows, we will only consider thin lenses. In optical schemes, thin lenses are depicted as segments with arrows at the ends. Depending on the direction of the arrows, the diagrams distinguish between collecting and diffusing lenses.

Consider how a beam of rays parallel to the main optical axis passes through the lens. Coming through

a collecting lens, the rays are collected at one point. Having passed through the scattering lens, the rays diverge in different directions in such a way that all their extensions converge at one point lying in front of the lens.

The point at which, after refraction in a converging lens, beams parallel to the main optical axis are collected, is called the main focus of the lens-F.

In a diffusing lens, rays parallel to its main optical axis are scattered. The point at which the extensions of the refracted rays are collected lies in front of the lens and is called the main focus of the diffusing lens.

The focus of the scattering lens is obtained at the intersection not of the rays themselves, but of their extensions, therefore, it is imaginary, in contrast to the converging lens, in which the focus is real.

The lens has two main focuses. Both of them lie at equal distances from the optical center of the lens on its main optical axis.

The distance from the optical center of the lens to the focus is usually called the focal length of the lens. The more the lens changes the direction of the rays, the shorter its focal length is. Therefore, the optical power of a lens is inversely proportional to its focal length.

Optical power, as a rule, is denoted by the letter "DE", and is measured in diopters. For example, when writing a prescription for glasses, they indicate how many diopters the optical power of the right and left lenses should be.

diopter (diopter) is the optical power of a lens, the focal length of which is 1m. Since the focuses of the collecting lenses are real, and the scattering ones are imaginary, we agreed to consider the optical power of the collecting lenses a positive value, and the optical power of the scattering lenses - negative

Who established the law of light reflection?

For the 16th century, optics was a cutting edge science. From a glass ball filled with water, which was used as a focusing lens, a magnifying glass emerged, and from it a microscope and a telescope. The largest naval power in those days, the Netherlands needed good telescopes in order to consider a dangerous coast ahead of time or to get away from the enemy in time. Optics ensured the success and reliability of navigation. Therefore, it was in the Netherlands that many scientists were engaged in it. The Dutchman Willebrord, Snell van Royen, who called himself Snellius (1580-1626), observed (which, however, many had seen before him), how a thin ray of light was reflected in a mirror. He simply measured the angle of incidence and the angle of reflection of the beam (which no one had done before) and established the law: the angle of incidence is equal to the angle of reflection.

A source. Mirrored world. Gilde V. - M .: Mir, 1982. 24.

Why are diamonds so highly valued?

Obviously, a person especially appreciates everything that does not lend itself or is difficult to change. Including precious metals and stones. The ancient Greeks called the diamond "adamas" - irresistible, which expressed their special attitude to this stone. Of course, in rough stones (diamonds were not cut either), the most obvious properties were hardness and brilliance.

Diamonds have a high refractive index; 2.41 - for red and 2.47 - for violet (for comparison, suffice it to say that the refractive index of water is 1.33, and glass, depending on the type, is from 1.5 to 1.75).

White light is composed of the colors of the spectrum. And when its ray is refracted, each of the constituent colored rays is deflected in a different way, as if it splits into the colors of the rainbow. That is why there is a "play of colors" in the diamond.

The ancient Greeks were undoubtedly fascinated by this too. Not only is the stone exceptional in brilliance and hardness, it also has the shape of one of Plato's "perfect" bodies!

Experiments

EXPERIENCE in optics # 1

Explain the darkening of a block of wood after wetting it.

Equipment: a vessel with water, a wooden block.

Explain the oscillation of the shadow of a stationary object as light passes through the air above a burning candle. Equipment: tripod, ball on a thread, candle, screen, projector.

Stick colored pieces of paper on the fan blades and observe how the colors are added at different rotation modes. Explain the observed phenomenon.

EXPERIENCE # 2

By light interference.

Simple demonstration of light absorption by an aqueous dye solution

Requires for its preparation only a school light, a glass of water and a white screen. Dyes can be very diverse, including fluorescent.

Students observe with great interest the color change of a white light beam as it propagates through the dye. The color of the beam emerging from the solution turns out to be unexpected for them. Since the light is focused by the illuminator lens, the color of the spot on the screen is determined by the distance between the glass of liquid and the screen.

Simple experiments with lenses. (EXPERIENCE # 3)

What happens to the image of an object obtained with the lens if part of the lens is broken and the image is taken with the rest of it?

Answer . The image will turn out in the same place where it was obtained with the whole lens, but its illumination will be less, because the smaller part of the rays coming out of the object will reach its image.

Place a small shiny object, such as a ball from a bearing, or a bolt from a computer, on a table lit by the sun (or a powerful lamp) and look at it through a tiny hole in a piece of foil. Multi-colored rings, or ovals, will be clearly visible. What kind of phenomenon will be observed? Answer. Diffraction.

Simple experiments with colored glasses. (EXPERIMENT # 4)

On a white sheet of paper, write “excellent” with a red felt-tip pen or pencil and “good” with a green felt-tip pen. Take two shards of bottle glass - green and red.

(Attention! Be careful, you can injure yourself on the edges of the debris!)

What glass do you need to look through to see an “Excellent” grade?

Answer . You must look through the green glass. In this case, the inscription will be visible in black on a green background of the paper, since the red light of the inscription “excellent” is not transmitted by the green glass. When viewed through red glass, the red lettering will not be visible on the red background of the paper.

EXPERIENCE # 5: Observing the phenomenon of dispersion

It is known that when a narrow beam of white light is passed through a glass prism, a rainbow strip can be observed on a screen mounted behind the prism, which is called the dispersion (or prismatic) spectrum. This spectrum is also observed when a light source, a prism and a screen are placed in a closed vessel from which air is evacuated.

The results of the last experiment show that there is a dependence of the absolute refractive index of glass on the frequency of light waves. This phenomenon is observed in many substances and is called light dispersion. There are various experiments to illustrate the phenomenon of light dispersion. The figure shows one of the options for its implementation.

The dispersion of light was discovered by Newton and is considered one of his most important discoveries. The tombstone, erected in 1731, depicts the figures of young men holding the emblems of Newton's most important discoveries. In the hands of one of the young men - a prism, and in the inscription on the monument there are the following words: "He investigated the difference between light rays and the various properties of flowers that appear at the same time, which no one previously suspected."

EXPERIENCE # 6: Does a mirror have a memory?

How to put a flat mirror on a drawn rectangle to get an image: a triangle, a quadrangle, a pentagon. Equipment: a flat mirror, a sheet of paper with a square drawn on it.

QUESTIONS

Transparent plexiglass becomes dull when rubbed with sandpaper. The same glass becomes transparent again if you rub it ...How?

On the scale of the lens diaphragm, numbers are applied equal to the ratio of the focal length to the diameter of the hole: 2; 2.8; 4.5; 5; 5.8, etc. How will the exposure time change if the aperture is moved to a larger division of the scale?

Answer. The higher the aperture value indicated on the scale, the lower the illumination of the image, and the longer the shutter speed required when photographing.

Most often, camera lenses consist of several lenses. Light passing through the lens is partially reflected from the lens surfaces. What defects does this lead to when shooting?Answer

When photographing snowy plains and water surfaces on sunny days, it is recommended to use a solar hood, which is a cylindrical or conical tube blackened inside, put on
lens. What is the purpose of the hood?Answer

To prevent light from reflecting inside the lens, a thinnest transparent film of the order of ten thousandths of a millimeter is applied to the surface of the lenses. Such lenses are called coated lenses. What physical phenomenon is lens enlightenment based on? Explain why lenses do not reflect light.Answer.

Question for forum

Why does black velvet seem so much darker than black silk

Why does the white light, passing through the window glass, not decompose into its components?Answer.

Blitz

1. What are the glasses without temples called? (Pince-nez)

2. What gives out an eagle while hunting? (Shadow.)

3. What is the famous artist Quinji for? (Ability to portray the transparency of air and moonlight)

4. What are the names of the lamps that illuminate the stage? (Soffits)

5. Is it a blue or greenish gemstone?(Turquoise)

6. Indicate where the fish is in the water if the fisherman sees it at point A.

Blitz

1. What can't you hide in a chest? (A ray of light)

2. What color is white light? (White light consists of a series of multi-colored rays: red, orange, yellow, green, blue, blue, violet)

3. Which is bigger: a cloud or a shadow from it? (The cloud casts a full shadow cone tapering to the ground, the height of which is large due to the large size of the cloud. Therefore, the cloud shadow differs little in size from the cloud itself)

4. You follow her, she is from you, you are from her, she is after you. What it is? (Shadow)

5. The edge is visible, but you won't get there. What is this? (Horizon)

Optical illusions.

Don't you think that black and white stripes are moving in opposite directions? If you tilt your head - now to the right, then to the left - the direction of rotation also changes.

Endless staircase leading up.

Sun and eye

do not be like the sun of the eyes,

He could not see the Sun ... W. Goethe

The juxtaposition of the eye and the sun is as old as the human race itself. The source of this comparison is not science. And in our time, next to science, simultaneously with the picture of phenomena, revealed and explained by new natural science, the world of ideas of the child and primitive man continues to exist and, intentionally or unintentionally, the world of poets imitating them. It is sometimes worth looking into this world as one of the possible sources of scientific hypotheses. He is amazing and fabulous; in this world, bridges-connections are boldly thrown between the phenomena of nature, which sometimes science does not yet suspect. In some cases, these connections are guessed correctly, sometimes they are fundamentally wrong and simply ridiculous, but they always deserve attention, since these errors often help to understand the truth. Therefore, it is instructive to approach the question of the connection between the eye and the Sun first from the point of view of childhood, primitive and poetic ideas.

Playing hide and seek, a child very often decides to hide in the most unexpected way: he closes his eyes or covers them with his hands, being sure that no one will see him now; for him, vision is identified with light.

Even more surprising, however, is the preservation of the same instinctive confusion of sight and light in adults. Photographers, that is, people somewhat sophisticated in practical optics, often catch themselves closing their eyes when, when charging or developing the plates, one must carefully monitor so that light does not penetrate into a dark room.

If you listen carefully to how we speak, to our own words, then here, too, traces of the same fantastic optics are immediately discovered.

Without noticing this, people say: "the eyes sparkled," "the sun has peeped out," "the stars are watching."

For poets, transferring visual representations to a luminary and, conversely, attributing the properties of light sources to the eyes is the most common, one might say, mandatory technique:

The stars of the night

Like accusatory eyes

They are looking at him mockingly.

His eyes are shining.

A.S. Pushkin.

We looked at the stars with you

They are on us. Fet.

How does a fish see you?

Because of the refraction of light, the fisherman sees the fish not where it really is.

Folk omens

Introduction

1.Literary review

1.1. The history of the development of geometric optics

1.2. Basic concepts and laws of geometric optics

1.3. Prism elements and optical materials

2. Experimental part

2.1 Materials and experimental technique

2.2. Experimental results

2.2.1. Demonstration experiments using a glass prism with a refractive angle of 90º

2.2.2. Demonstration experiments using a glass prism filled with water, with a refractive angle of 90º

2.2.3. Demonstration experiments using a hollow glass prism, and filled with air, with a refractive angle of 74º

2.3. Discussion of experimental results

List of used literature

Introduction

The decisive role of experiment in the study of physics at school corresponds to the main principle of the natural sciences, in accordance with which experiment is the basis for cognition of phenomena. Demonstration experiments contribute to the creation of physical concepts. Among the demonstration experiments, one of the most important places is occupied by experiments in geometric optics, which make it possible to clearly show the physical nature of light and demonstrate the basic laws of light propagation.

In this work, the problem of setting up experiments in geometric optics using a prism in high school is investigated. The most illustrative and interesting experiments in optics were selected using equipment that can be purchased by any school or made independently.

Literature review

1.1 The history of the development of geometric optics.

Optics belongs to such sciences, the initial ideas of which arose in ancient times. Throughout its centuries-old history, it has experienced continuous development, and at present it is one of the fundamental physical sciences, enriching itself with the discoveries of more and more new phenomena and laws.

The most important problem of optics is the question of the nature of light. The first ideas about the nature of light appeared in ancient times. Ancient thinkers tried to understand the essence of light phenomena based on visual sensations. The ancient Hindus thought that the eye was of a "fiery nature." The Greek philosopher and mathematician Pythagoras (582-500 BC) and his school believed that visual sensations arise due to the fact that "hot vapors" emanate from the eyes to objects. In their further development, these views took on a clearer form in the form of the theory of visual rays, which was developed by Euclid (300 BC). According to this theory, vision is due to the fact that "visual rays" emanate from the eyes, which feel with their ends of the body and create visual sensations. Euclid is the founder of the doctrine of the rectilinear propagation of light. Applying mathematics to the study of light, he established the laws of light reflection from mirrors. It should be noted that for the construction of a geometric theory of light reflection from mirrors, the nature of the origin of light does not matter, but only the property of its rectilinear propagation is important. The patterns found by Euclid are preserved in modern geometric optics. The refraction of light was also familiar to Euclid. At a later time, similar views were developed by Ptolemy (70-147 AD). They paid great attention to the study of the phenomena of light refraction; in particular, Ptolemy made many measurements of the angles of incidence and refraction, but he failed to establish the law of refraction. Ptolemy noticed that the position of the luminaries in the sky changes due to the refraction of light in the atmosphere.

In addition to Euclid, other ancient scientists knew the effect of concave mirrors. Archimedes (287-212 BC) is credited with burning the enemy fleet using a system of concave mirrors, which he used to collect the sun's rays and direct it to Roman ships. A certain step forward was made by Empedocles (492-432 BC), who believed that outflows are directed from luminous bodies to the eyes, and outflows emanate from the eyes toward the bodies. When these outflows meet, visual sensations arise. The famous Greek philosopher, founder of atomism, Democritus (460-370 BC) completely rejects the concept of visual rays. According to the views of Democritus, vision is due to the fall on the surface of the eye of small atoms emanating from objects. Epicurus (341-270 BC) later adhered to similar views. The famous Greek philosopher Aristotle (384-322 BC), who believed that the cause of visual sensations lies outside the human eye, was also a decisive opponent of the "theory of visual rays". Aristotle made an attempt to explain colors as a consequence of the mixture of light and darkness.

It should be noted that the views of ancient thinkers were mainly based on the simplest observations of natural phenomena. Ancient physics did not have the necessary foundation in the form of experimental research. Therefore, the teaching of the ancients about the nature of light is speculative. Nevertheless, although these views are for the most part only ingenious guesses, they certainly had a great influence on the further development of optics.

The Arab physicist Algazen (1038) developed a number of problems in optics in his research. He studied the eye, refraction of light, reflection of light in concave mirrors. When studying the refraction of light, Algazey, in contrast to Ptolemy, proved that the angles of incidence and refraction are not proportional, which was the impetus for further research in order to find the law of refraction. Algazen knows the magnifying power of spherical glass segments. On the question of the nature of light, Alhazen takes the right positions, rejecting the theory of visual rays. Algazen proceeds from the idea that rays emanate from each point of a luminous object, which, reaching the eye, cause visual sensations. Alhazen believed that light has a finite speed of propagation, which in itself represents a major step in understanding the nature of light. Alhazen correctly explained that the Sun and Moon appear larger on the horizon than at their zenith; he attributed this to a deception of the senses.

Renaissance. In the field of science, the experimental method of studying nature is gradually winning. During this period, a number of outstanding inventions and discoveries were made in optics. Francis Mavrolik (1494-1575) is credited with a fairly accurate explanation of the glasses. Mavrolik also found that concave lenses do not collect but scatter rays. He found that the lens is the most important part of the eye, and made a conclusion about the causes of hyperopia and myopia as a consequence of the abnormal refraction of light by the lens. Next, we should mention the Italian Port (1538-1615), who in 1589 invented the camera obscura - the prototype of the future camera. A few years later, the main optical instruments were invented - the microscope and the telescope.

The invention of the microscope (1590) is associated with the name of the Dutch master optician Zachary Jansen. Telescopes began to be manufactured at about the same time (1608-1610) by Dutch opticians Zachary Jansen, Jacob Metzius and Hans Lippersgey. The invention of these optical instruments led in the following years to major discoveries in astronomy and biology. The German physicist and astronomer N. Kepler (1571-1630) carried out fundamental works on the theory of optical instruments and physiological optics, the founder of which he can rightfully be called. Kepler worked a lot on the study of light refraction.

Fermat's principle, named after the French scientist Pierre Fermat (1601-1665), who formulated it, was of great importance for geometric optics. This principle established that light between two points spreads along such a path, which takes a minimum of time to travel. It follows from this that Fermat, in contrast to Descartes, considered the speed of propagation of light to be finite. The famous Italian physicist Galilei (1564-1642) did not carry out systematic work devoted to the study of light phenomena. However, in optics, he also owns works that have brought science remarkable results. Galileo improved the telescope and first applied it to astronomy, in which he made outstanding discoveries that contributed to the substantiation of the latest views on the structure of the Universe, based on the Copernican heliocentric system. Galileo managed to create a telescope with a frame magnification of 30, which was many times greater than the magnification of the telescopes of its first inventors. With its help, he discovered mountains and craters on the surface of the Moon, discovered satellites near the planet Jupiter, discovered the stellar structure of the Milky Way, etc. Galileo tried to measure the speed of light in terrestrial conditions, but was unsuccessful due to the weakness of the experimental means available for this purpose ... Hence it follows that Galileo already had the correct idea of ​​the final speed of light propagation. Galileo also observed sunspots. The priority of the discovery of sunspots by Galileo was challenged by the Jesuit scientist Pater Scheiner (1575-1650), who made precise observations of sunspots and solar torches using a telescope arranged according to Kepler's scheme. The remarkable thing about Scheiner's work is that he turned the telescope into a projection device, extending the eyepiece more than was necessary for clear vision with the eye, this made it possible to get an image of the Sun on a screen and demonstrate it at different degrees of magnification to several faces at the same time.

The 17th century is characterized by further progress in various fields of science, technology and production. Mathematics is undergoing significant development. Scientific societies and academies uniting scientists are being created in various European countries. Thanks to this, science becomes the property of wider circles, which contributes to the establishment of international relations in science. In the second half of the 17th century, the experimental method of studying natural phenomena finally won out.

The largest discoveries of this period are associated with the name of the brilliant English physicist and mathematician Isaac Newton / (1643-1727). The most important experimental discovery of Newton in optics is the dispersion of light in a prism (1666). Investigating the passage of a beam of white light through a triangular prism, Newton found that a beam of white light splits into an infinite collection of colored rays that form a continuous spectrum. From these experiments, it was concluded that white light is a complex radiation. Newton also made the opposite experiment, collecting with the help of a lens colored rays formed after a ray of white light passed through a prism. As a result, he again received white light. Finally, Newton conducted an experiment of color mixing using a rotating circle divided into several sectors, painted in the primary colors of the spectrum. When the disc rotated quickly, all the colors merged into one, giving the impression of white.

The results of these fundamental experiments Newton laid the foundation for the theory of colors, which had not been possible before by any of his predecessors. According to the theory of colors, the color of a body is determined by those rays of the spectrum that this body reflects; the body absorbs other rays.

1.2 Basic concepts and laws of geometric optics. The branch of optics, which is based on the concept of light rays as straight lines along which light energy propagates, is called geometric optics. This name was given to it because all the phenomena of the propagation of light here can be investigated by means of geometric constructions of the path of rays, taking into account the law of reflection and refraction of light. This law is the foundation of geometric optics.

However, where we are talking about phenomena, the interaction of light with obstacles, the dimensions of which are small enough, the laws of geometric optics are insufficient and it is necessary to use the laws of wave optics. Geometric optics makes it possible to disassemble the main phenomena associated with the passage of light through lenses and other optical systems, as well as with the reflection of light from mirrors. The concept of a light ray as an infinitely thin beam of light propagating rectilinearly naturally leads to the laws of rectilinear propagation of light and independent propagation of light beams. It is these laws, together with the laws of refraction and reflection of light, that are the basic laws of geometric optics, which not only explain many physical phenomena, but also allow calculations and design of optical devices. All these laws were initially established as empirical, that is, based on experiments, observations.

LIGHT SCATTERING

Particles of a substance that transmits light behave like tiny antennas. These "antennas" receive light electromagnetic waves and transmit them in new directions. This process is called Rayleigh scattering after the English physicist Lord Rayleigh (John William Strett, 1842-1919).

Test 1

Place a sheet of white paper on a table, and next to it a flashlight, so that the light source is in the middle of the long side of the sheet of paper.
Fill two colorless clear plastic glasses with water. Use a marker to mark the glasses with the letters A and B.
Add a drop of milk to glass B and stir
Fold a 15x30 cm sheet of white cardboard together with the short ends and fold it in half to form a hut. It will serve as a screen for you. Place the screen in front of the flashlight, on the opposite side of the sheet of paper.

Darken the room, turn on the flashlight and notice the color of the light spot formed by the flashlight on the screen.
Place glass A in the center of the sheet of paper, in front of the flashlight, and do the following: notice the color of the light spot on the screen, which is formed as a result of the passage of light from the flashlight through the water; take a close look at the water and notice how the color of the water has changed.
Repeat the steps replacing glass A with glass B.

As a result, the color of the light spot formed on the screen by a beam of light from a flashlight, in the path of which there is nothing but air, can be white or slightly yellowish. When a beam of light passes through clear water, the color of the spot on the screen does not change. The color of the water also does not change.
But after passing the beam through water to which milk is added, the light spot on the screen appears yellow or even orange, and the water becomes bluish.

Why?
Light, like electromagnetic radiation in general, has both wave and corpuscular properties. The propagation of light has a wave-like character, and its interaction with matter occurs as if the light radiation consists of individual particles. Light particles - quanta (aka photons), are bunches of energy with different frequencies.

Photons have both particle and wave properties. Since photons experience wave vibrations, the wavelength of light of the corresponding frequency is taken as the size of the photon.
The lantern is a source of white light. This is visible light, consisting of all sorts of shades of colors, i.e. radiation of different wavelengths - from red, with the longest wavelength, to blue and violet, with the shortest wavelengths in the visible range. When light vibrations of different wavelengths are mixed, the eye perceives them and the brain interprets this combination as white, i.e. lack of color. Light passes through clear water without taking on any color.

But when the light passes through the water tinted with milk, we notice that the water has become bluish, and the light spot on the screen is yellow-orange. This happened as a result of scattering (deflection) of part of the light waves. Scattering can be elastic (reflection), in which photons collide with particles and bounce off them, just like two billiard balls bounce off each other. A photon undergoes the greatest scattering when it collides with a particle of about the same size as itself.

Small particles of milk in water scatter best the short wavelengths blue and violet. Thus, when white light passes through water tinted with milk, a pale blue sensation arises from the scattering of short wavelengths. After scattering on milk particles of short wavelengths from the light beam, mainly yellow and orange wavelengths remain in it. They move on to the screen.

If the particle size is greater than the maximum wavelength of visible light, the scattered light will be composed of all wavelengths; this light will be white.

Test 2

How does scattering depend on particle concentration?
Repeat the experiment using different concentrations of milk in water, from 0 to 10 drops. Observe the changes in the colors of the water and the light transmitted by the water.

Test 3

Does the scattering of light in a medium depend on the speed of light in this medium?
The speed of light depends on the density of the substance in which the light travels. The higher the density of the medium, the slower the light propagates in it.

Remember that the scattering of light in different substances can be compared by observing the brightness of these substances. Knowing that the speed of light in air is 3 x 108 m / s, and the speed of light in water is 2.23 x 108 m / s, you can compare, for example, the brightness of wet river sand with the brightness of dry sand. It should be borne in mind that the light falling on the dry sand passes through the air, and the light falling on the wet sand - through the water.

Pour sand into a disposable paper plate. Pour some water over the edge of the plate. Having noted the brightness of different areas of the sand in the plate, draw a conclusion in which sand the dispersion is greater: in dry (in which grains of sand are surrounded by air) or in wet (grains of sand are surrounded by water). You can try other liquids as well, such as vegetable oil.

Most people, remembering their school years, are sure that physics is a very boring subject. The course includes many tasks and formulas that will not be useful to anyone in later life. On the one hand, these statements are true, but like any subject, physics has another side of the coin. Only not everyone discovers it for themselves.

A lot depends on the teacher

Perhaps our education system is to blame for this, or maybe the whole thing is in the teacher, who only thinks about the fact that it is necessary to reprimand the material approved from above, and does not seek to interest his students. Most often it is he who is to blame. However, if the children are lucky, and the lesson is taught by a teacher who loves his subject himself, then he will be able not only to interest the students, but also help them discover something new. As a result, the children will start to attend such classes with pleasure. Of course, formulas are an integral part of this academic subject, there is no getting away from it. But there are also positive aspects. Experiments are of particular interest to schoolchildren. We will talk about this in more detail. Here are some fun physics experiences you can have with your child. It should be interesting not only for him, but also for you. It is likely that with the help of such activities you will instill in your child a genuine interest in learning, and "boring" physics will become his favorite subject. it is not difficult to carry out, this will require very few attributes, the main thing is that there is a desire. And maybe then you can replace your child's school teacher.

Consider some interesting physics experiments for little ones, because you need to start small.

Paper fish

To carry out this experiment, we need to cut out a small fish from thick paper (you can use cardboard), the length of which should be 30-50 mm. We make a round hole in the middle with a diameter of about 10-15 mm. Next, from the side of the tail, cut a narrow channel (3-4 mm wide) to a round hole. Then we pour water into a basin and carefully place our fish there so that one plane lies on the water, and the other remains dry. Now you need to drop oil into the round hole (you can use an oiler from a sewing machine or bicycle). The oil, trying to spill over the surface of the water, will flow along the cut channel, and the fish, under the influence of the oil flowing back, will float forward.

Elephant and Pug

We will continue to carry out entertaining experiments in physics with our child. We invite you to introduce your kid to the concept of a lever and how it helps to facilitate a person's work. For example, share that it can easily lift a heavy cabinet or sofa. And for clarity, show an elementary experiment in physics with the use of a lever. To do this, we need a ruler, a pencil and a couple of small toys, but always of different weights (that's why we called this experiment "The Elephant and the Pug"). We attach our Elephant and Pug to different ends of the ruler using plasticine, or ordinary thread (we just tie toys). Now, if you put the ruler with the middle part on a pencil, then, of course, the elephant will drag, because it is heavier. But if you move the pencil towards the elephant, then the Pug will easily outweigh it. This is the principle of leverage. The ruler (lever) rests on the pencil - this place is the fulcrum. Further, the child should be told that this principle is used everywhere, it is the basis for the operation of a crane, swing and even scissors.

Home experience in physics with inertia

We'll need a jar of water and a utility net. It will not be a secret for anyone that if an open jar is turned over, water will pour out of it. Let's try? Of course, for this it is better to go outside. We put the can in the grid and begin to smoothly swing it, gradually increasing the amplitude, and as a result we make a full revolution - one, second, third, and so on. No water is poured out. Interesting? Now let's make the water pour up. To do this, take a tin can and make a hole in the bottom. We put it in the grid, fill it with water and start rotating. A jet gushes from the hole. When the can is in the lower position, this does not surprise anyone, but when it flies up, the fountain continues to beat in the same direction, and not a drop from the neck. That's it. All this can explain the principle of inertia. When the bank rotates, it tends to fly away straight, and the grid does not let it go and forces it to describe circles. Water also tends to fly by inertia, and in the case when we made a hole in the bottom, nothing prevents it from escaping and moving in a straight line.

Surprise box

Now let's look at experiments in physics with displacement. You need to put a matchbox on the edge of the table and move it slowly. The moment it passes its average mark, a fall will occur. That is, the mass of the part extended beyond the edge of the tabletop will exceed the weight of the remaining one, and the boxes will tip over. Now let's shift the center of mass, for example, put a metal nut inward (as close to the edge as possible). It remains to place the boxes in such a way that a small part of it remains on the table, and a large part hangs in the air. The fall will not happen. The essence of this experiment is that the entire mass is above the fulcrum. This principle is also used throughout. It is thanks to him that furniture, monuments, transport, and much more are in a stable position. By the way, the children's toy Vanka-vstanka is also built on the principle of displacement of the center of mass.

So, we will continue to consider interesting experiments in physics, but we will move on to the next stage - for schoolchildren in the sixth grade.

Water carousel

We need an empty tin can, a hammer, a nail, a rope. We punch a hole in the side wall at the very bottom with a nail and a hammer. Further, without pulling the nail out of the hole, bend it to the side. It is necessary that the hole is oblique. We repeat the procedure on the second side of the can - you need to do it so that the holes turn out opposite each other, but the nails are bent in different directions. In the upper part of the vessel we punch two more holes, through them we pass the ends of a rope or thick thread. We hang the container and fill it with water. Two oblique fountains will begin to beat from the lower holes, and the can will begin to rotate in the opposite direction. Space rockets work on this principle - the flame from the nozzles of the engine beats in one direction, and the rocket flies in the other.

Experiments in physics - grade 7

Let's experiment with mass density and find out how you can make an egg float. Experiments in physics with different densities are best done using the example of fresh and salt water. Take a jar filled with hot water. We put an egg in it, and it will immediately drown. Next, pour table salt into the water and stir. The egg begins to float, and the more salt, the higher it will rise. This is because salt water has a higher density than fresh water. So, everyone knows that in the Dead Sea (its water is the saltiest) it is almost impossible to drown. As you can see, experiments in physics can significantly increase your child's horizons.

and a plastic bottle

Seventh grade students begin to study atmospheric pressure and its effect on the objects around us. To expand on this topic deeper, it is better to conduct appropriate experiments in physics. Atmospheric pressure affects us, although it remains invisible. Let's take an example with a balloon. Each of us can cheat him. Then we place it in a plastic bottle, put the edges on the neck and fix it. Thus, air can only enter the balloon, and the bottle will become an airtight vessel. Now let's try to inflate the balloon. We will not succeed, since the atmospheric pressure in the bottle will not allow us to do this. When we blow, the ball begins to displace the air in the vessel. And since our bottle is airtight, it has nowhere to go, and it begins to shrink, thereby becoming much denser than the air in the ball. Accordingly, the system is leveled and the balloon cannot be inflated. Now let's make a hole in the bottom and try to inflate the balloon. In this case, there is no resistance, the displaced air leaves the bottle - the atmospheric pressure is equalized.

Conclusion

As you can see, experiments in physics are not at all complicated and quite interesting. Try to interest your child - and learning for him will be completely different, he will start to attend classes with pleasure, which in the end will affect his academic performance.