Výuková centra Projekt č. CZ.1.07/1.1.03/

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1 Výuková centra Projekt č. CZ.1.07/1.1.03/01.0057
© Letohradské soukromé gymnázium o.p.s.

2 Elektromagnetizmus Elektromagnet
Magnetické vlastnosti elektrického proudu Magnetické pole kolem vodiče s elektrickým proudem Magnetické pole cívky Magnetické pole cívky a směr el.proudu v cívce Homogenní magnetické pole Působení magnetického pole na vodič Vzájemné působení vodičů Stejnosměrný elektromotor Střídavý elektromotor

3 Elektromagnet cívka s proudem + jádro z měkké ocele = elektromagnet
How can electricity be used to make a magnet? In this experiment you used electricity to make a temporary magnet, called an electromagnet. As long as the electric current was on, the iron crane was a magnet and could pick up ferromagnetic objects. When the electricity was turned off, the magnetizing cause was no longer present, so the object was not attracted to the iron crane. So, let's see how electricity is able to make a magnet. cívka s proudem + jádro z měkké ocele = elektromagnet princip – když cívkou teče el.proud, chová se jako magnet a jádro zesiluje jeho magnetické účinky

4 Magnetické vlastnosti elektrického proudu
Discuss what happens to a compass when a wire with electrical current is near. Describe the relationship between electricity and magnetism Why does the compass respond when it is near an electrical wire with current flowing through it? We can conclude from this experiment that an electric current causes a magnetic field around it just like a magnet causes a magnetic field. When you moved the compass near a bar magnet, the needle pointed toward the magnet's magnetic field and not toward the north. When you put the compass near the electrical wire with current flowing through it, the compass did not point north; instead, the compass needle pointed in the direction of the current's magnetic field. What would happen if we put a ferromagnetic object into the magnetic field? Now we have established that a conductive wire with a current flowing through it has a magnetic field. If we put a ferromagnetic object in this magnetic field, the object will concentrate the strength of the field and cause the object to become magnetic. Once the current flow in the line stops, the magnetic field disappears and the object stops acting like a magnet. However, the magnetic field of one wire is small and does not have much strength, so it can only make temporary magnets from small objects. But, let’s say that we take a wire and coil it several times to form a long coiled piece of electrical wire, and then we turn on the current. We would have a magnetic field much bigger and stronger than we would without the coiled piece of wire, and we could magnetize even larger objects. An iron bar placed through the center of the coiled wire would become a temporary magnet, called an electromagnet, as long as the electric current is flowing through the wire. Whenever current travels through a conductor, a magnetic field is generated, a fact famously stumbled upon by Hans Christian Ørsted around Depending on the shape of the conductor, the contour of the magnetic field will vary. If the conductor is a wire, however, the magnetic field always takes the form of concentric circles arranged at right angles to the wire. The magnetic field is strongest in the area closest to the wire, and its direction depends upon the direction of the current that produces the field, as illustrated in this applet. vodič, jímž prochází proud, vytváří kolem sebe magnetické pole

5 Magnetické pole kolem vodiče s elektrickým proudem
směr magnetické síly v  poli kolem vodiče znázorňují magnetické indukční čáry magnetické indukční čáry mají tvar soustředných kružnic ležících v rovinách kolmých na vodič orientace magn. ind. čar závisí na směru proudu Discuss what happens to a compass when a wire with electrical current is near. Describe the relationship between electricity and magnetism Why does the compass respond when it is near an electrical wire with current flowing through it? We can conclude from this experiment that an electric current causes a magnetic field around it just like a magnet causes a magnetic field. When you moved the compass near a bar magnet, the needle pointed toward the magnet's magnetic field and not toward the north. When you put the compass near the electrical wire with current flowing through it, the compass did not point north; instead, the compass needle pointed in the direction of the current's magnetic field. What would happen if we put a ferromagnetic object into the magnetic field? Now we have established that a conductive wire with a current flowing through it has a magnetic field. If we put a ferromagnetic object in this magnetic field, the object will concentrate the strength of the field and cause the object to become magnetic. Once the current flow in the line stops, the magnetic field disappears and the object stops acting like a magnet. However, the magnetic field of one wire is small and does not have much strength, so it can only make temporary magnets from small objects. But, let’s say that we take a wire and coil it several times to form a long coiled piece of electrical wire, and then we turn on the current. We would have a magnetic field much bigger and stronger than we would without the coiled piece of wire, and we could magnetize even larger objects. An iron bar placed through the center of the coiled wire would become a temporary magnet, called an electromagnet, as long as the electric current is flowing through the wire. Whenever current travels through a conductor, a magnetic field is generated, a fact famously stumbled upon by Hans Christian Ørsted around Depending on the shape of the conductor, the contour of the magnetic field will vary. If the conductor is a wire, however, the magnetic field always takes the form of concentric circles arranged at right angles to the wire. The magnetic field is strongest in the area closest to the wire, and its direction depends upon the direction of the current that produces the field, as illustrated in this applet.

6 Magnetické pole kolem vodiče s elektrickým proudem
Ampérovo pravidlo pravé ruky nám pomůže určit orientaci pole: uchopíme-li vodič do pravé ruky tak, aby palec ukazoval směr proudu ve vodiči, pokrčené prsty ukazují pak směr indukčních čar palec ukazující směr proudu ve vodiči The Right Hand Rule, illustrated below, simply shows how a current-carrying wire generates a magnetic field. If you point your thumb in the direction of the current, as shown, and let your fingers assume a curved position, the magnetic field circling around those wires flows in the direction in which your four fingers point. prsty ukazující orientaci indukčních čar vodič s proudem

7 Magnetické pole cívky magnetické pole cívky je podobné magnetickému poli tyčového magnetu. Ampérovo pravidlo pravé ruky nám pomůže určit orientaci magn. pole: pravou ruku po- ložíme na cívku (závit) tak, aby pokrčené prsty ukazovaly směr proudu v cívce, pak palec ukazuje směr ind. čar v dutině cívky

8 Magnetické pole cívky a směr proudu v cívce
když změníme směr proudu procházející cívkou na opačný, změní se i orientace magnetického pole cívky na opačnou

9 Homogenní magnetické pole
mezi dvěma póly podkovovitého magnetu a uvnitř cívky (v jeho střední části) jsou magnetické indukční čáry navzájem rovnoběžné a stejně vzdálené - je zde tedy homogenní magnetické pole

10 Působení magn.pole na vodič
na vodič s proudem působí v magn.poli magnetická síla směr síly závisí na poloze magnetu vůči vodiči a na směru proudu procházejícího vodičem

11 Působení magn.pole na vodič
na vodič s proudem působí v magn.poli magnetická síla směr síly závisí na poloze magnetu vůči vodiči a na směru proudu procházejícího vodičem

12 Působení magn.pole na vodič
na vodič s proudem působí v magn.poli magnetická síla směr síly závisí na poloze magnetu vůči vodiči a na směru proudu procházejícího vodičem

13 Působení magn.pole na vodič
směr magnetické síly směr ind. čar směr proudu The Left Hand Rule shows what happens when charged particles (such as electrons in a current) enter a magnetic field. You need to contort your hand in an unnatural position for this rule, illustrated below. As you can see, if your index finger points in the direction of a magnetic field, and your middle finger, at a 90 degree angle to your index, points in the direction of the charged particle (as in an electrical current), then your extended thumb (forming an L with your index) points in the direction of the force exerted upon that particle. This rule is also called Fleming's Left Hand Rule, after English electronics pioneer John Ambrose Fleming, who came up with it. Flemingovo pravidlo levé ruky nám pomůže určit směr síly, kterou pole působí na vodič: položíme-li otevřenou levou ruku k vodiči tak, aby prsty ukazovaly směr proudu a indukční čáry vstupovaly do dlaně, odtažený palec nám ukazuje směr magnetické síly působící na vodič

14 Vzájemné působení vodičů
Proud protéká ve vodičích stejným směrem : v opačných směrech : dva rovnoběžné vodiče, jimiž protéká proud, na sebe působí magnetickou silou přitahují se, teče-li proud v obou vodičích stejným směrem, a odpuzují se, teče-li proud ve vodičích v navzájem opačných směrech

15 Stejnosměrný elektromotor
funkce elektromotoru : přeměňuje elektrickou energii na pohybovou (otáčivý pohyb) princip : cívka s proudem se chová jak magnet a nachází se v magn. poli trvalého magnetu, co vyvolá její otočení o 180° proud teče z + pólu baterie přes kartáč do komutátoru a do cívky díky odděleným půlkám komutátoru se směr proudu , který teče cívkou, mění po každé půl-otáčce na opačný a to se stále opakuje popis : stator (nepohyblivá část, trvalý magnet tvaru podkovy) rotor (otáčející se část, cívka s proudem, ozn.také jako kotva) komutátor (kruhová část s dvěma oddělenými půlkruhy - modrým a červeným, je zapojený do elektrického obvodu přes 2 kartáče, mění směr proudu v cívce rotoru) Popis elektromotoru: stator, rotor(tady baterie+ cívka=elektromagnet), komutátor The motor features a permanent horseshoe magnet (called the stator because it’s fixed in place) and an turning coil of wire called an armature (or rotor, because it rotates). The armature, carrying current provided by the battery, is an electromagnet, because a current-carrying wire generates a magnetic field; invisible magnetic field lines are circulating all around the wire of the armature. The key to producing motion is positioning the electromagnet within the magnetic field of the permanent magnet (its field runs from its north to south poles). The armature experiences a force described by the left hand rule. This interplay of magnetic fields and moving charged particles (the electrons in the current) results in the torque (depicted by the green arrows) that makes the armature spin. Use the Flip Battery button to see what happens when the flow of current is reversed. Take advantage of the Applet Speed slider and Pause button to visualize these forces better. A single, 180-degree turn is all you would get out of this motor if it weren't for the split-ring commutator — the circular metal device split into halves (shown here in red and blue) that connects the armature to the circuit. Electricity flows from the positive terminal of the battery through the circuit, passes through a copper brush to the commutator, then to the armature. But this flow is reversed midway through every full rotation, thanks to the two gaps in the commutator. This is a clever trick: For the first half of every rotation, current flows into the armature via the blue portion of the commutator, causing current to flow in a specific direction (indicated by the black arrows). For the second half of the rotation, though, electricity enters through the red half of the commutator, causing current to flow into and through the armature in the opposite direction. This constant reversal essentially turns the battery's DC power supply into alternating current, allowing the armature to experience torque in the right direction at the right time to keep it spinning.

16 Střídavý elektromotor
funkce elektromotoru : přeměňuje elektrickou energii na pohybovou From what you have observed in this experiment here, can you explain how an electric motor works? Why is important that alternating current is supplied to our houses? How does magnetism make an electric motor operate? An electric motor converts electric energy into mechanical energy that can be used to do work. In the experiment we first use DC current to flow through the wire. Remember that DC current flows in only one direction unless there is a switch to reverse its direction. When the current is first turned on, the like magnetic poles are near each other. Recall from past experiments that like magnetic poles repel each other, and they are forced to move away from each other. Since the electromagnet is free to move, its south pole moves away from the south pole of the fixed magnet. However, as it rotates it moves closer to the north pole of the fixed magnet and is pulled toward it by an attracting force because unlike magnetic poles attract each other. When we reverse the direction of the current flow, the location of the poles change places, and again, you have two like poles near each other. This arrangement causes the electromagnet to rotate again as the like poles are forced away from each other and the unlike poles attract each other. Then, again, the movement stops until the current is reversed and the magnetic poles in the electromagnet change places another time. We can conclude that each time the current flow is reversed in the wire, the electromagnet moves in response to the repelling force of like poles and the attracting force of unlike poles. This movement of the electromagnet, in turn, rotates the shaft to which it is connected-and mechanical energy is created. The rotating shaft can be connected to various other components to create moving parts that can do work. AC current, by nature, is constantly changing the direction of flow and does not need a reversing switch. So, when AC current is run through the wire, the electromagnet continues to rotate without stopping. This happens because the locations of the magnetic poles are continually changing places and attracting or repelling the magnetic poles of the fixed permanent magnet. neobsahuje komutátor a rotor není tvořen trvalým magnetem neustálou změnu směru proudu zabezpečuje elektromagnet, který tvoří stator elektromotoru používá se ve vysavačích, k pohonu tramvají,, lokomotiv apod.

17 Výuková centra Projekt č. CZ.1.07/1.1.03/01.0057
© Letohradské soukromé gymnázium o.p.s.