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Magnetism

Magnetism. Magnets and Magnetic Fields. Naturally occurring Attract or repel each other Attract certain metals (iron, cobalt, nickel) Point in a given direction relative to the Earth when allowed to hang freely North and South poles- there are NO monopole magnets! Opposite poles attract.

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Magnetism

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  1. Magnetism

  2. Magnets and Magnetic Fields • Naturally occurring • Attract or repel each other • Attract certain metals (iron, cobalt, nickel) • Point in a given direction relative to the Earth when allowed to hang freely • North and South poles- there are NO monopole magnets! • Opposite poles attract

  3. Just as an electric charge is surrounded by an electric field, a moving electric charge is also surrounded by a MAGNETIC FIELD. Similar to how a planet orbits the sun and rotates on its own axis, an electron orbits the nucleus and spins on its own axis. The MAGNETIC FIELD is due to both the orbital motion as the electron orbits the nucleus and the spin of each electron around its own axis

  4. “Ferromagnetic” elements include iron, cobalt, and nickel and have unpaired electrons with the same spin. Paired electrons have opposite spin, which would cancel the effect. Therefore, these atoms are naturally “magnetic”. If the magnetic fields of large clusters of those atoms, called “domains” are aligned, the whole material is magnetized. Not every piece of iron is a magnet. Only those pieces whose domains are all aligned!

  5. S N Magnetic fields are created by Magnetic materials ( those spinning electrons!) A magnetic field, B, is represented by magnetic field lines that point OUT of the north pole and INTO the south pole B

  6. Magnetic fields are also created by Current-carrying wires (a lot of moving charges!) The direction of the magnetic field, B, is determined using a “right-hand rule”. The magnetic field encircles the wire.

  7. Magnetic fields encircle Current-carrying wires Some people are afraid to live near electric lines for fear of the magnetic fields around the wires. There is no definitive evidence of danger due to living near these magnetic fields.

  8. The Earth behaves like a giant bar magnet. This is due to the movement of Earth’s molten interior (lots of moving charges). • The magnetic poles do NOT line up with the geographic poles. • Under the North geographic pole lies a South magnetic pole! • The direction of Earth’s magnetic field is not rigidly fixed and moves around from year to year. • The poles have completely reversed numerous times (about every 100,000 years) according to geological evidence.

  9. Magnets and Current-Carrying Wire • A wire with current running through it produces a magnetic field around the wire. • Electromagnets (or solenoids) are magnetic only when current flows.

  10. A MOTOR is a machine that converts electricity into mechanical motion. Most motors use electromagnets to produce rotation. A motor has a rotor spinning with coils of current carrying wires passing magnets. Michael Faraday is credited with building the first electric motor

  11. A generatordoes the reverse of a motor: it converts mechanical motion into electricity! Examples: a wind or water turbine, steam engine Who is credited with making the first generator? Yes, Michael Faraday!

  12. The “Flip-Side” Currents in wires produce magnetic fields (example: electromagnets) AND Changing magnetic fields produce currents in wires….

  13. Michael Faraday Michael Faraday studied both electricity and its relationship to magnetism. We remember the “Faraday cage” that protects its contents from static charges. The unit for capacitance is the Farad. He also made the first electric motor and generator and transformer! Faraday’s Law states that a changing magnetic field will “induce” a current in a wire.

  14. Changing magnetic fields induce a current in wires: The metal detector One application of Faraday’s law is the security metal detector at the airport. As a person passes through the detector, which is a large electromagnet, any metal on their person will change the magnetic field in the detector, inducing a current that signals the presence of metal!

  15. Changing magnetic fields induce a current in wires - Another application of Faraday’s Law:The Electric Guitar The “pickup” in an electric guitar contains a coil of wire wrapped around a magnet. The vibration of the guitar string causes the magnet to vibrate. The changing magnetic field induces a current in the coil of wire. The current is sent to the amplifier to produce the sound.

  16. Changing magnetic fields induce a current in wires: Electric Generators (and alternators) All generators use rotation of an apparatus with wires and magnets. The rotation causes the magnetic fields to be constantly changing. Changing magnetic field induce current in the wires = electricity!

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