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Transcript
Magnets Magnets Level 5 Physics January 2013 Material adapted from MIT 8.02 course notes Magnets Magnet Types Permanent Magnets Electron Magnetic Dipole A closed loop of current is know as a magnetic dipole, µ. The spin of electrons creates a magnetic field related to that caused by a magnetic dipole. Magnets Magnet Types Permanent Magnets Electron Magnetic Dipole A closed loop of current is know as a magnetic dipole, µ. The spin of electrons creates a magnetic field related to that caused by a magnetic dipole. Different magnetic properties of materials result from interaction of these magnetic dipole moments. Magnets Magnet Types Permanent Magnets Ferromagnetism Ferromagnetic materials have strong interactions between permanent neighboring atomic dipole moments. Magnets Magnet Types Permanent Magnets Ferromagnetism Ferromagnetic materials have strong interactions between permanent neighboring atomic dipole moments. When an external magnetic field is applied, these dipole moments align to the external magnetic field. Magnets Magnet Types Permanent Magnets Ferromagnetism Ferromagnetic materials have strong interactions between permanent neighboring atomic dipole moments. When an external magnetic field is applied, these dipole moments align to the external magnetic field. Ferromagnetic materials include iron, nickel, and cobalt. Magnets Magnet Types Permanent Magnets Permanent Magnets With ferromagnetic materials, the alignment of the neighboring atomic dipoles will remain even when the external magnetic field is removed. Magnets Magnet Types Permanent Magnets Permanent Magnets With ferromagnetic materials, the alignment of the neighboring atomic dipoles will remain even when the external magnetic field is removed. This leaves a permanent magnet, which are formed today from alloys of ferromagnetic materials. Common alloys include Alnico: Aluminum, Nickel, Cobalt Neodymium: Neodymium, Iron, Boron Magnets Magnet Types Electromagnets Electromagnets As we have seen, the flow of electric current produces a magnetic field. Magnets produced in this manner are called electromagnets and involve wrapping a wire around a core, often creating a solenoid or toroid. Magnets Magnet Types Electromagnets Electromagnet Principles The advantage with electromagnets over permanent magnets is that the magnetic field strength can be changed by varying the electric current. Magnets Magnet Types Electromagnets Electromagnet Principles The advantage with electromagnets over permanent magnets is that the magnetic field strength can be changed by varying the electric current. Often, an electromagnet is constructed by winding wire around an iron core, which causes the magnetic field strength inside the electromagnet to increase due to the ferromagnetic properties of iron. Magnets Magnet Types Electromagnets Electromagnet Applications Electromagnets are used in a wide array of applications, including Motors and Generators Transformers Magnetic recording devices (ex. hard drives) Loudspeakers Medical imaging devices (ex. MRI) Magnets Magnet Types Electromagnets Electromagnet Applications Electromagnets are used in a wide array of applications, including Motors and Generators Transformers Magnetic recording devices (ex. hard drives) Loudspeakers Medical imaging devices (ex. MRI) Often, applications of electromagnetics involve a principle called induction, where a changing magnetic field causes an induced voltage.
