The nature of the reflection of light depends on the direction in which the surface on which it falls is curved. For example, the concave surface of a spoon produces inverted images, while its back side reflects images correctly. The determining factor in the orientation of the reflected image is the shape of the reflector.
Concave surfaces, such as the inside of a hollow sphere or the face of a spoon, usually produce inverted images. Convex surfaces, such as the outside of a sphere or the back of a spoon, maintain the correct image orientation.
Concave mirrors reflect parallel rays of light inward, directing them to a single point called the focus or focal point. At the point where the image is formed, the light rays intersect. If the object reflected by a concave mirror is located closer to the mirror than the focal point, the resulting image will be oriented correctly. If an object is behind the focal point, its reflection will be upside down. As for reflections created by convex surfaces, they are always oriented correctly, since such surfaces cause light rays to diverge. As a result, the reflected rays never cross each other and therefore do not form an inverted image.
Enlarged image The panda (P") (picture above) appears in a spherical concave mirror when the panda (P) is between the mirror and the focal point (F). The image is formed at the intersection of the reflected rays.
When parallel rays reflected from the concave surface of a spherical mirror, they converge at a focal point.
The image remains upside down and appears normal in size when the panda is in the center of a spherical mirror.
Inverted image decreases as the panda moves away from the center of the spherical mirror.
Inverted, but the still magnified image appears when the panda is between the focal point and the center of the sphere.
Images in a convex mirror
The image reflected by a convex mirror is always reduced and oriented correctly, no matter how far away the object is. Because convex mirrors provide a wider field of view (picture on the right) than flat mirrors, they are convenient for use as rear-view mirrors in cars.
Faces in a spoon
The inner and outer surfaces of the spoon act similarly to the concave and convex surfaces of a spherical mirror. Since the focal point of the inner surface of the spoon is a short distance from it, the reflection of the face will always be upside down. The convex back of the spoon always produces a reduced image with the correct orientation.
REFLECTION IN A SPOON
Mirrors in the funhouse create very funny reflections. This effect is created using curved mirrors.
Take a metal spoon, polished to a shine, in your hand. The spoon has two sides - convex and concave. Hold the spoon vertically straight in front of you and look at the convex part of the spoon. What does your image look like? Do you see yourself upright or upside down? Is the reflection stretched? If so, what do you look like - taller or fatter?
Now turn the spoon horizontally. How did this change the image?
Again, hold the spoon vertically, but turn it over so that you are facing the concave side of the spoon. What does your reflection look like now? Is it upside down? Have your features changed?
Now turn the spoon horizontally again. How did this affect the image? Slowly bring the spoon closer to your eyes. Has the image been turned upside down, or is everything still the same?
Reflection distortion is caused by the fact that the mirror surface is curved.
When parallel rays hit a curved surface, they are reflected at slightly different angles. This divergence and convergence of the rays is what makes the reflection look so funny.
CROVE MIRROR FROM WRAP
These days, wrappers are increasingly made from thin plastic film. Some of them, especially gift ones, have a silver-plated reflective surface. You've probably received a gift wrapped in such packaging film. If so, I wonder what you did with the mirror wrap? We hope you saved it for your next experience.
Cut out a rectangle from the silver-plated film the same size as the card. Using a glue stick, carefully glue the film to the card: first fold them and slowly, from the middle to the edges, smooth the film to get rid of air bubbles. Wait until the glue dries.
Now look at the silver plated card. Do you see your reflection in it? Did you get a good mirror?
Now try to bend the “mirror”. Holding the card by the edges, bend it so that it forms a convex mirror. In this case, the central part of the card should look at you. Now move this fold closer to the edge of the card. How did your reflection change? What happens if you change the bending angle of the “mirror”?
Now make a concave mirror out of the card. Can you determine the distance at which your reflection turns upside down?
A good mirror usually has a very smooth silvered surface. For example, the back side of the glass is coated with silver paint (more precisely, mercury paint, the so-called amalgam). The packaging film is, of course, not such a good mirror. Even though it is coated with silver paint, it is not that smooth. Small convexities and concavities in the film greatly impair its reflective properties.
TRANSPARENT MIRROR
Turn on the lights in your room brighter. Take the silver wrapping film in your hands and pull it tight. Hold it at arm's length and look at your image.
Now bring the film closer to your face so that it touches your nose. Can you see through it what is in the room?
Now ask a friend to look at your face behind the film. Make funny faces and ask your friend to guess what you are doing. Even though your friend won't see what's going on, you can see everything! Of course, the image will be blurry, but still visible!
This wrapping film is a good one-way mirror. This property is created by a very thin layer of silver paint. Just like on a one-way mirror, the layer of paint is not so thick as to block all the light, some of the light still passes in.
In order to increase the effect of one-way transmission of light, the object on one side of the glass should be brightly illuminated, and on the other side there should be much less light.
Municipal educational institution
middle School of General education
Novaya Bekshanka village, municipal district "Baryshsky district"
Ulyanovsk region
Research project
on the topic of:
Completed : Okolnov Victor and
Okolnov Dmitry,
3rd grade students.
Managers : Elizarova Olga Nikolaevna,
Ilyichev Alexander Nikolaevich
2013/2014 academic year
Content.
1 . Abstract to the project
2.Introduction. The mystery of the tablespoon.
2. Reflection in a spoon.
3.Optical experiments.
4.Note. From the history of a spoon.
5.Using a spoon.
6. Conclusion.
7. List of references.
annotation
to a research project
“What is the mystery of the spoon?”
3rd grade students
Municipal educational institution secondary school in the village of Novaya Bekshanka
Okolnov Victor and Okolnov Dmitry .
This work tells in an interesting way about the amazing property of one of the most necessary household items, the secret of the spoon.
The fact is that the polished surface of the spoon reflects light and creates images, like a mirror. The only difference is that the mirror we are used to is flat, and the spoon is convex-concave. On the inside, the spoon is a concave mirror, which, in most cases, reverses the image, and on the outside, it is a convex mirror, forming only direct and reduced images. Therefore, in the convex part we are reflected directly, and in the concave part we are reflected upside down. To understand why a concave mirror inverts the image, but a convex mirror does not, the guys developed a plan to find the answer to this question and thought through the plan for their project.
Under the guidance of a physics teacher, students conducted several experiments in which they clearly demonstrated the properties of concave and convex mirrors and lenses.
Students conducted a painstaking study of concave and convex mirrors in an accessible and understandable manner; the areas of application of convex and concave surfaces were considered. The objectives and goals of the study have been achieved.
A colorful presentation is the completion of a research project and is accompanied by large photo and video materials.
This research project and presentation can be used by primary school teachers both in environmental lessons and in extracurricular activities.
Work leaders: /Elizarova O.N./
_________________ / Ilyichev A.N./
1. Introduction.
The topic of our work is “What is the mystery of the spoon?” We took this topic because the spoon is an integral part of our everyday life.
« A spoon is dear to dinner,” says a Russian proverb. And it’s not for nothing that this proverb mentions a spoon, because a spoon is the most practical item of all cutlery. Despite the fact that the spoon is designed to carry liquid or semi-liquid food, it can be used as a fork, as a knife, and as a ladle. Some spoons are successfully used for decorationpremises. Or you can use it as a mirror.
One day, while having lunch after school, my brother and I noticed an unusual picture: one side of the spoon magnified our reflection, and the other side turned it over. Why is this happening?
Object of study : tablespoon
Subject of study : learning the secrets of light and reflection
Problem : Why is a person reflected upside down on one side of the spoon, but normally on the other?
Research hypothesis : Let's assume that this is such an unusual mirror.
The goal is practical : find the answer to the question, learn about the properties of reflection and distortion of light, prepare a presentation and tell your classmates about it.
Research objectives :
Search for information in books and the Internet on the research problem.
Learn the secrets of light and reflection.
Find applications of concave and convex mirrors
Research methods : analysis, generalization, .
Practical significance : developing interesting material for classmates, creating a booklet, designing a presentation.
2.History of the tablespoon
“A spoon is dear to dinner,” says a Russian proverb. And it’s not for nothing that this proverb mentions a spoon, because a spoon is the most practical item of all cutlery. Despite the fact that the spoon is designed to carry liquid or semi-liquid food, it can be used as a fork, as a knife, and as a ladle. Some spoons are successfully used to decorate a room. Particularly suitable for this purpose wooden spoons with painting, they are not only very beautiful, but also functional.
The first spoons were not made of stone, as one might assume, but of baked clay, since they did not require strength, because soft food was then eaten with spoons. It was a hemisphere with a handle. Later, people began to use various materials to make spoons. In the 15th century, spoons made of brass and copper became popular. Aristocrats and kings used spoons made of silver and gold. The shape of the spoon was constantly changing until in 1760 it became oval and easy to use. Nowadays a huge number of different spoons are made - different colors, sizes, shapes, from different materials.
3.Reflections in a tablespoon
The fact is that the polished surface of the spoon reflects light and creates images, like a mirror. The only difference is that the mirror we are used to is flat, and the spoon is convex-concave. On the inside, the spoon is a concave mirror, which, in most cases, reverses the image, and on the outside, it is a convex mirror, forming only direct and reduced images. Therefore, in the convex part we are reflected directly, and in the concave part we are reflected upside down. To understand why a concave mirror reverses the image, but a convex mirror does not, let us remember what an image is in general. These are rays of light entering our eyes. An inverted image is when the head is below and the legs are above, that is, when the upper ray has become the lower and vice versa. In order to get an inverted image, you need to send rays of light so that they change places. This is exactly what a concave mirror does. It collects the light falling on it “in a heap” (i.e., it focuses the light), and then the rays simply fly in a straight line. A convex mirror does not focus the rays, but rather scatters them in all directions. But the top ray remains the top ray, and the image does not flip.
4.Optical experiments
Physics laboratory
We work with optics equipment
We build an inverted image.
We study the properties of convex and concave lenses.
Entertaining optical experiments
at home
CROVE MIRROR FROM WRAP
These days, wrappers are increasingly made from thin plastic film. Some of them, especially gift ones, have a silver-plated reflective surface. You've probably received a gift wrapped in such packaging film. If so, I wonder what you did with the mirror wrap?
Cut out a rectangle from the silver-plated film the same size as the card. Using a glue stick, carefully glue the film to the card: first fold them and slowly, from the middle to the edges, smooth the film to get rid of air bubbles. Wait until the glue dries.
Now look at the silver plated card. Do you see your reflection in it? Did you get a good mirror?
Now try to bend the “mirror”. Holding the card by the edges, bend it so that it forms a convex mirror. In this case, the central part of the card should look at you. Now move this fold closer to the edge of the card. Now look and smile!
MIRROR ROOM
Devices and materials
: three small rectangular mirrors, plasticine, a small bead or toy, rubber rings, tape.
Progress
Use tape and rubber bands to secure the three mirrors to form a triangle. Place a bead or toy in the center of this little “mirror room.” Look carefully in the middle. What do you see? (You will see multiple reflections)
KALEIDOSCOPE
Devices and materials
: three small rectangular mirrors, plasticine, colored transparent beads or small toys, adhesive tape, tracing paper.
Progress
Using plasticine, attach three mirrors to form a triangle. Use tracing paper and tape to cover one of the holes. Place the beads and look into the free end of the tube. What do you see? Shake the pipe, what do you see now?
(You will see multiple reflections of the beads. However, the figure formed by three mirrors limits the number of reflections. Each image appears connected to its two neighbors.)
5.Application of convex and concave mirrors Concave mirrors .
Nowadays, concave mirrors are more often used for lighting. IN pocket electric flashlightthere is a tiny light bulb only a few candles long. If it sent its rays in all directions, then such a flashlight would be of little use: its light would not penetrate further than one or two meters. But behind the light bulb there is a small concave mirror. Therefore, the beam of light from a flashlight cuts through the darkness ten meters ahead. However, the lantern also has a small lens in front of the light bulb. The mirror and lens help each other create a directed beam of light.
Car headlights and spotlights, the reflector of a blue medical lamp, a ship's lantern on the top of a mast and a lighthouse lantern are also arranged in the same way. In the spotlight a powerful arc lamp shines. But if the concave mirror were taken out of the spotlight, the light of the lamp would aimlessly spread out in all directions; it would shine not over seventy kilometers, but only one or two...
Particularly complex lighthouse lantern. In ancient times, the most powerful lighthouse was the Alexandria Lighthouse - the last of the wonders of the world associated with the name of Alexander the Great
English scientist Isaac Newton used a concave mirror in a telescope. And modern telescopes also use concave mirrors.
But the concave ones radio telescope antennasvery large diameter from many individual metal mirrors.
Convex mirrors.
So convex and unbreakable mirrors can often be seen on city streets and in public places.
Installation of road mirrors on roads with limited visibility allows you to protect vehicles and people. These mirrors are equipped with reflective elements along the contour and glow in the dark, reflecting the light of car headlights.
Dome mirrorsfor indoors they are a mirror hemisphere, with a viewing angle reaching 360 degrees. In this case, the mirror is mounted mainly on the ceiling.
Review mirrorsused both on streets and indoors. So, for example, in a store, an overview shows the staff who is doing what in the aisles between the shelves, and in a difficult part of the parking lot it allows car owners to perform maneuvers without collisions.
In medicine, the most common mirror is the frontal reflector - a concave mirror with a hole in the middle, designed to direct a narrow beam of light into the eye, ear, nose, pharynx and larynx. Mirrors of various designs and shapes are also used for research in dentistry and surgery. 5 . Photographic materials.
Surely you have at least once looked into a spoon as if into a mirror. If not, find the nearest spoon and look at its concave surface. Your reflection will be upside down! In this article we will try to figure out why this happens. By and large, a spoon is a curved mirror, so we need to learn to explain what we see in mirrors, including mirrors of complex shapes.
Zero mirrors. Let's start with the simplest thing: let's try to understand how we see objects. Simple - said loudly: various details and features of our vision can be discussed endlessly. We will only need to know that a ray of light, reflected from an object, hits our eye - that’s why we see this object. This is shown schematically in Figure 1.
One mirror. However, the beam can enter our eye not directly, but by being reflected along the way from the mirror. The following law holds true: the angle of incidence is equal to the angle of reflection. This means that the angles marked in Figure 2 are equal.
For our purposes, it will be more convenient to think of this whole process a little differently. Let's mentally place on the other side of the mirror a whole behind-the-mirror world, symmetrical to the ordinary one. Then the mirror will become a window into this looking glass. Indeed, let's look at Figure 3: since the angle of incidence is equal to the angle of reflection, Quantik, looking into the mirror along the beam AX, will see a flower into which the reflected ray rests XB. But if the beam AX passed through the mirror as if through a window (that is, it would go further along the beam XB′), he would have run into a symmetrical mirror flower, that is, Quantik would have seen the same thing.
One tilted mirror. What happens if you tilt the mirror, for example, towards yourself? Where then will Quantik’s mirror double be (let’s call him Kitnavk - this is the word Quantik read backwards)? Let's use a trick: let's turn not the mirror, but Quantik. After all, all that is important to us is the relative position of Quantik and the mirror. You see what happens in Fig. 4, A. Now let’s rotate the whole picture, putting Quantik in place (Fig. 4, b). As a result, Quantik will see the legs in front of him, and not the face of Kitnavka.
This result is easy to check: looking in the mirror, tilt it towards yourself - the reflection will rise, tilt it away from you - the reflection will fall.
Lots of mirrors. Now let's place many small mirrors along an arc of a circle. Already resembles a big spoon, doesn’t it? First, let's place Quantik in the center of this circle. Then Quantik will see his face in the center of each mirror. After all, no matter what mirror he looks at, the “ray of his sight” will be perpendicular to the mirror, and the mirror will not be tilted relative to this “ray of sight”.
If now Quantik moves away, then relative to the new “rays of sight” the upper mirrors will be tilted towards Quantik, and the lower ones - away from him (see Fig. 5). Therefore, in the center of the upper mirror, Quantik will see the legs of the upper Kitnavka, and in the center of the lower mirror - the top of the lower Kitnavka’s head. In total, in the mirrors, from top to bottom, individual parts of Kitnavka are visible, not yet inverted, but in order from bottom to top.
Let's glue together the reflections. It’s not so easy to imagine what Quantik will eventually see. Let's do an experiment with something simpler, like a triangle. First, cut it into four parts, and then fold these parts in the reverse order (Fig. 6). The result will be something awkward. But if you make at least eight parts, the result will already resemble an inverted triangle. And the more parts into which we cut the triangle, the less noticeable the roughness in the image assembled backwards.
The same will happen with Kitnavk. Quantik will essentially look into many narrow slits, in each of which a piece of Kitnavka is visible. Together they will assemble into a rough inverted Kitnavka, just as we had an inverted triangle before.
One curved mirror. All you have to do is imagine that the spoon consists of very small flat mirrors. So small that from our point of view they merge into a continuous curved surface, and the individual reflections in each of them form a continuous inverted image.
Now try to answer a couple of questions yourself: |
Artist Sergey Chub
In the section on the question Why is the reflection in the spoon upside down? given by the author Partition the best answer is The fact is that the polished surface of the spoon reflects light and creates images, like a mirror. The only difference is that the mirror we are used to is flat, and the spoon is convex-concave.
On the inside, the spoon is a concave mirror, which, in most cases, reverses the image, and on the outside, it is a convex mirror, forming only direct and reduced images. Therefore, in the convex part we are reflected directly, and in the concave part we are reflected upside down.
To understand why a concave mirror inverts the image, but a convex mirror does not, let us remember what an image is in general. These are rays of light entering our eyes. An inverted image is when the head is below and the legs are above, that is, when the upper ray has become the lower and vice versa. In order to get an inverted image, you need to send rays of light so that they change places. This is exactly what a concave mirror does. It collects the light falling on it “in a heap” (i.e., it focuses the light), and then the rays simply fly in a straight line.
A convex mirror does not focus the rays, but rather scatters them in all directions. But the top ray remains the top ray, and the image does not flip.
