2Magnetismus Magnety a jejich vlastnosti Působení magnetu na tělesa z různých látekFeromagnetizmus, magnety trvalé a dočasnéMagnetické domény a magnetováníMagnetické pole a magnetické indukční čáryMagnetické pole Země, kompas
3Magnety a jejich vlastnosti dva magnety se můžou navzájem :přitahovat ( opačnými póly)odpuzovat ( souhlasnými póly)popis magnetu :S a J pól ( na opačných koncích)netečné pásmo ( uprostřed )
7Působení magnetu na tělesa z různých látek A magnet is any piece of iron, steel, or magnetite that has the property of attracting iron or steel..magnetem označujeme těleso z ocele, ze železa, příp.magnetovce, niklu a kobaltu, které dokáže přitahovat jiné magnety
8Feromagnetizmus, magnety trvalé a dočasné přírodní magnety a materiály, které se dají zmagnetovat ozn.jako feromagnetické materiálydělíme je na trvalé a dočasné, po zmagnetovánítrvalý magnet si dlouhodobě udrží magnetické vlastnosti (např.železo, tvrdá ocel)dočasný magnet bez přítomnosti magnetizujícího tělesa magnetické vlastnosti rychle ztratí (např.měkká ocel)
9Magnetické domény a magnetování magnetické domény jsou malé, asi 1 mm 3 oblastimagnetu, projevující se jako elementární magnetyMagnetism may be naturally present in a material or the material may be artificially magnetized by various methodsPermanent magnets are usually more difficult to magnetize, but they remain magnetized. Materials which can be magnetized are called ferromagnetic materials.A magnetic domain is region in which the magnetic fields of atoms are grouped together and aligned. In the experiment below, the magnetic domains are indicated by the arrows in the metal material. You can think of magnetic domains as miniature magnets within a material. In an unmagnetized object, like the initial piece of metal in our experiment, all the magnetic domains are pointing in different directions. But, when the metal became magnetized, which is what happens when it is rubbed with a strong magnet, all like magnetic poles lined up and pointed in the same direction. The metal became a magnet. It would quickly become unmagnetized when its magnetic domains returned to a random order. The metal in our experiment is a soft ferromagnetic material, which means that it is easily magnetized but may not retain its magnetism very long.What happened to the piece of metal when you rubbed a strong magnet across it the first time? The second time? What do the arrows in the material represent? Why do they become lined up when the magnet is brought in contact with the metal? If you wanted to turn a paper clip into a magnet, how do you think you could do it? What is different about ferromagnetic materials that make them strongly magnetic?In ferromagnetic materials, the magnetic moments of a relatively large number of atoms are aligned parallel to each other to create areas of strong magnetization within the material. These areas, which are approximately a millimeter in size, contain billions of aligned atoms and are called magnetic domains. Magnetic domains are always present in ferromagnetic materials due to the way the atoms bond to form the material. However, when a ferromagnetic material is in the unmagnetized condition, the magnetic domains are randomly oriented so that the magnetic field strength in the piece of material is zero.za běžných okolností jsou magnetické domény náhodně uspořádanémagnetováním se všechny magnetické domény pod vlivem vnějšího magnetu uspořádají stejně
10Magnetické pole a magnetické indukční čáry The magnetic field of a bar magnet can be investigated with a compass needle. The magnetic poles of both bar magnet and compass needle are symbolized by the following colours:north poleredsouth polegreenIf you move the magnetic needle with pressed mouse button, the magnetic field line through the center of the compass needle will be drawn with blue colour. The blue arrows mark the direction of the magnetic field which is defined as the direction indicated by the north pole of the compass needle. If you turn the magnet by using the red button, the direction of the field lines will reverse. The left button makes it possible to clear all field lines.
11Magnetické pole a indukční čáry magn.pole – je prostor kolem magnetu, ve kterém magnet působímagn. indukční čáry- myšlené čáry, které zviditelňují magnet.polesměr šípky – udává směr orientace magnetky v magn.poliorientace magn. indukční čar - je vždy od S pólu magnetu k J pólu magnetu
12Magnetické pole a indukční čáry oblasti nejsilnějšího magnetického pole – u pólůoblasti slabého magnetického pole – v oblasti netečného pásma, daleko od zdrojehustota mag. indukčních čar –udává sílu mag.poleThe lines that we have mapped out around the magnet, called the magnetic lines of force, indicate the region in which the force of the magnet can be detected. This region is called the magnetic field. If an iron object is near a magnet, but is not within the magnetic field, the object will not be attracted to the magnet. When the object enters the magnetic field, the force of the magnet acts, and the object is attracted. The pattern of these lines of force tells us something about the characteristics of the forces caused by the magnet. The magnetic lines of force, or flux, leave the north pole and enter the south pole.
13Magnetické pole a indukční čáry Magnets are surrounded by magnetic fields. A magnetic field can be thought of as consisting of lines of force. The forces of magnetic attraction and repulsion move along the lines of force. The magnet below is being placed on a surface containing iron filings.The iron filings line up along the magnetic field lines of the magnet. Note the circular pattern of the field lines. By convention, we say that the field lines emanate from the north pole of the magnet and re-enter the magnet through the south pole. Note also that the field lines are closer together at the poles than at the center of the magnet. More iron filings are attracted to the poles because the strength of the magnetic field is greater at the poles.The forces of magnetic attraction and repulsion move along the lines of force. The magnets below are on a virtual surface containing iron filings.The iron filings line up along the magnetic field lines of the magnets. Note the pattern of the field lines when unlike poles are placed opposite each other. Unlike poles attract each other. Note the difference in the pattern of field lines when like poles are placed opposite each other. Like poles repel each other.What is happening when iron particles are sprinkled over and around the magnets?Do you see any differences in the patterns in each of the three situations? If so, what differences do you see?What do the patterns indicate in each situation? Can you tell by these patterns where the magnetic forces might be the strongest? The weakest? Can you tell by these patterns where the magnetic forces are attracting? Repelling?What does the pattern made by the iron particles indicate?You learned in a previous experiment that no matter how many pieces you cut a magnet into, each piece is still a magnet. Even if you shred a magnet into particles the size of sand, each tiny grain is a magnet with a north pole and a south pole. When these magnetized particles are sprinkled over the magnet in Box A, the resulting pattern shows the magnetic field around a single magnet. We can see that the force of the magnet is the strongest at the two ends because more iron particles are concentrated in these areas. The magnetic lines of flux flow from one end to the other.How do you explain what is occurring?To understand what is happening, recall from a previous experiment that a magnet allowed to stand freely, like a compass needle, will point to the north in response to the earth’s magnetic field unless it is near a strong magnetic. If the compass is near a strong bar magnet, the opposite poles of the magnets are attracted to each other. We can use this knowledge to identify the magnetic field of a magnet by placing a compass at various locations around the bar magnet and observing where the compass needle points. If the compass is far away from the bar magnet the compass will always point north because it is not in the bar magnet’s magnetic field. As it gets closer to the magnet, the compass begins to point more and more toward the magnet as a result of the force, or the magnetic field, of the magnet. The compass needle aligns itself with the magnetic flux lines of the magnet.What if...Let's say that instead of using one compass to move around the bar magnet, we place thousands of tiny compass needles all around the bar magnet and watch which direction they point and what pattern they make. That is what is happening in our experiment with the iron filings. Each tiny magnetic iron filing is a tiny magnet with a north and south pole, just like a tiny compass. When the iron filings are sprinkled, those very close to the magnet, where the magnetic force is the strongest, will cling to the magnet.Those filings a little farther away, where the magnetic force is less strong, will align themselves with the magnetic flux lines, but they will not be drawn to cling to the magnet. Those filings even farther away, outside the magnetic force, will point north in response to the earth’s magnetic field. These patterns formed by the direction of the tiny compasses can tell us something about where the magnetic force is the strongest, where it is an attracting force, and where it is a repelling force. In Box B, this pattern indicates a repelling force because the tiny magnets are moving away from the ends of the larger bar magnets. Looking at the pattern in Box C, you see that the two ends of these magnets are attracted because the tiny magnets appear to be lined end to end, attracting to one another and also attracting to the ends of the larger bar magnets.
14Magnetické pole Země, kompas síla působící na magnetku kompasu má původ v magnetickém poli Zeměmagnetické pole Země je způsobeno pohybem horké a tekuté vrstvy vnějšího jádra Země, která obsahuje roztavené železomagnetické pole Země nás chrání před proudem nebezpečných částic ze Slunce tzv. slunečním větremseverní magnetický pól odpovídá jižnímu zeměpisnému póluThe invention of the magnetic compass, thought to have been independently developed in China and Europe during the 11th or 12th century, made navigation both by sea and land safer and much more accurate.What happened to the blue pole of the compass arrow when it was brought close to the north pole of the magnet? What happened to the blue pole of the compass arrow when it was brought close to the south pole of the magnet? What is a compass and what direction does it always point? What would you expect to happen if a magnet is suspended by a string and allowed to hang freely? From your observations, what can you conclude about the earth's magnetic properties?The needle of a compass is itself a magnet, and thus the north pole of the magnet always points north, except when it is near a strong magnet. In Experiment 1, when you bring the compass near a strong bar magnet, the needle of the compass points in the direction of the south pole of the bar magnet. When you take the compass away from the bar magnet, it again points north. So, we can conclude that the north end of a compass is attracted to the south end of a magnet.This can be a little confusing since it would seem that what we call the North Pole of the Earth is actually its magnetically south pole. Remember that a compass is a magnet and the north pole of a magnet is attracted to the south pole of a magnet.when you move the south pole of a magnet toward the south pole of another magnet, the two magnets repel each other and you cannot move them together. The rule for magnetic poles is that like poles repel each other and unlike poles attract each other.Since the north seeking pole of the compass needle is always attracted to the north, then the earth must be like a huge magnet with a magnetic pole at each end. This is exactly the case but magnetic north is slightly different from the north axis of rotation of the earth. Scientists believe that the movement of the Earth's liquid iron core and other things are responsible for the magnetic field around the earth.