Magnetic Fields

1. Chapter 24 Magnetic Fields

2. Northern Lights Aurora Borealis

3. Magnets has been known for more than 2000 years. Chinese Sailors used magnets as navigational compasses in 1500. Magnets are used in Electric generators, simple electric motors, television, computer screens, and tape recorders depend on the magnetic effects of electric currents.

6. Magnets always orient themselves in a north-south direction, because Earth is a giant magnet. The movement of electrically charged particles in the interior of planets generates the planets electric fields. Permanent magnets Are made of ALNICO V, an iron alloy containing 8% Aluminum, 14% Nickel, and 3% Cobalt. Magnetic forces are described by the existence of magnetic fields around magnets.

8. Magnetic field lines can be visualized as closed loops that leave the north pole of a magnet and enter the south pole.

9. Magnetic materials such as iron, cobalt, or nickel are attracted to a magnet. No magnetic materials such as copper and aluminum are not attracted to a magnet. The reason why a magnetic material is attracted to a magnet is because it becomes an "induced" magnet.

11. If you wrap a wire around an iron core, such as a nail, and you send electrical current through the wire, the nail will become highly magnetized. You can verify that by picking up small objects or by showing its effect on a compass. This is called the electromagnet. The strength or intensity of a coil's magnetic field depends on: The number of turns of wire in the coil. The amount of current flowing in the coil. The ratio of the coil length to the coil width. The type of material in the core. Electromagnetism

12. Magnetic field near a current-carrying wire. For the case of electric current moving through a wire, the resulting field is directed according to the "right hand rule". If the thumb of the right hand points along the wire from positive towards the negative side, then the magnetic field will wrap around the wire in the direction indicated by the fingers of the right hand.

13. When a wire is looped several times to form a coil and a current is allowed to flow through the coil, the field around all the loops is always in the same direction. A long coil of wire consisting of many loops is called a solenoid.

14. Magnetic field near a current-carrying coil. Grasp the coil in your left hand, with your fingers "wrapped around" in the direction of the electron current flow. Your thumb will then point toward the north pole of the coil.

15. Magnetic Domains:

16. Each electron in an atom acts like a tiny electromagnet. The magnetic fields of the electrons in a group of neighboring atoms can combine together and make a domain. When a piece of iron not in a magnetic field, the domains point in random directions. Their magnetic fields cancel one another. If iron is placed in magnetic field, the domains align with the external electric field. In temporary magnets, after the field is removed, the domains return to their random arrangement. In permanent magnets, the iron has been alloyed with other substances that keep the domains aligned after the field is removed. Electromagnets make up recording heads of audiocassette and videotape recorders.

17. Rocks that contain iron have recorded the history of the direction of Earth’s magnetic field. When seafloor rocks cooled after protruding from cracks from the molten rocks, they were magnetized in the direction of Earth’s field at that time. Since the seafloor spreads, rocks farther from the crack are older and had magnetization direction than those near the crack. As a conclusion, Earth’s north and south magnetic poles have exchanged places many times in Earth’s history.

18. Our planet's magnetic field varies with time, indicating it is not a static or fixed feature. Instead, some active process works to maintain the field. That process is most likely a kind of dynamic action in which the flowing and convecting liquid iron in Earth's outer core generates the magnetic field, geologists believe.