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Magnetic properties

Magnetic properties. Always a dipole (north and south) Opposites still attract and likes repel. (N attracts S) The Earth as a magnet because of its hot interior and its iron core. Compass use. The tip is a south pole and will point north. Naturally magnetic elements.

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Magnetic properties

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  1. Magnetic properties • Always a dipole (north and south) • Opposites still attract and likes repel. (N attracts S) • The Earth as a magnet because of its hot interior and its iron core. • Compass use. The tip is a south pole and will point north.

  2. Naturally magnetic elements • Iron: Constitutes much of the Earth’s core. Free electrons align themselves in one orientation in the presence of heat creating a magnetic field. • Permanent magnets can be created by subjecting ferromagnetic metals (e.g. Iron, nickel, and cobalt) to energy and they tend to cool with their electrons aligned. Those found in nature are called loadstone. • Some of these magnets last longer than others without being subjected to a constant flow of energy the electrons randomize losing the magnetic properties. So all magnets eventually lose their magnetic properties • HW p 206 1-6

  3. Field Lines • Imaginary north pole. These are similar to electric field lines. Imagine the force experienced by a tiny north pole, that is the direction of the field. Draw the lines for the following. • N N N S • S S

  4. Electromagnetism • Oersted discovered that a current carrying wire created a magnetic field. • There is a predictable nature of the magnetic field created by a current. • First right hand: What is the direction of the magnetic field created by a current carrying wire? • Point the thumb of your right hand in the direction of the current (+-)Your fingers will coil in the direction of the field. (NS) • HW 7-15 p. 207

  5. Given current predict field

  6. Using the Rule Which way is the field? Which way is the current? Given this field. Which way is the current? x x x x x . . . . . • Current direction given draw the field X

  7. Magnetic field created by a current carrying loop. • 2nd Right hand rule • For a current carrying loop, Coil the fingers of your right hand in the direction of the current. • Your thumb will point in the direction of the north pole magnetic field (Toward north) • When this wire loop surrounds a ferro-magnetic material it will become magnetic. (An Electromagnet)

  8. Magnetic field created by a current carrying loop. 2nd Right hand rule

  9. Electromagnetic interaction • Data storage • Magnetic Domains • Switching poles and dating the Earth proof of continental drift • Effect of magnetic fields on electromagnetic radiation. Refraction is greater for shorter λ. • Importance to life on the Earth

  10. Forces caused by magnetic fields • Force on a current carrying wire. • If a wire carrying a current passes through an existing magnetic field it will experience a force. • This force can cause the wire to move. • Predicting the direction of the force. 3rd Right hand Rule • Point the fingers of your right hand in the direction of the magnetic field (B) point the thumb of your right hand in the direction of the current (I). The force on the wire will come out of your palm. • HW 4-6 p. 563

  11. 3rd right hand rule

  12. Force on two parallel wires • Same direction opposite directions

  13. Which way is the force? xxxxxxx xxxxxxx ____________________________________ . . . . . . . . . . . . . .

  14. Force on a wire in a loop. • The portion of the loop that cuts the magnetic field experiences a force. • That force follows the 3rd right hand rule. • So as one side of the loop is being pushed up the other side where the current is reversed is being pushed down. • This causes a rotation of the loop. • Once the loop has rotated to a vertical position the direction of the current needs to be switched to keep it spinning in the same direction.

  15. Examine the loop Hooray Faraday!! Which way is the current moving?

  16. Uses of this phenomena Devices Varying current varies the magnetic field, moving the diaphragm. • Loud speakers • Hearing aids

  17. More uses Measuring current As the current changes so does the force. • Galvanometers (ammeters)

  18. Electric motor: electric energy to mechanical • Electric motors • Blenders • Cars • Drills • Lawn mowers • Washing machines • Etc. HW what is the function of the Armature and the commutator?

  19. Electromagnetic Induction • Electric current can be induced in a wire by simply moving a magnet near the wire. • When a conductor cuts through a magnetic field a force is put on the electrons in the conductor. (A potential difference (V) is created) • The amount of voltage created is proportional to the rate at which the field lines are cut and the amount of conductor cutting those lines.

  20. Faraday’s Discovery

  21. How do we make electricity? • How do we spin the magnet? Human power. • Steam engine. Think of the steam coming out of a tea kettle. • What is the source of energy we use to make steam? • Fossil fuels (Coal, Oil, Natural gas) • The Sun (Hydroelectric, Wind) • Nuclear • Geothermal

  22. Generator: mechanical to electric energy • Generators • Home generators • Power plants • Car alternators • Crank flashlights • Alt. energy sources • Wind mills • Hydroelectric • Water falls • River turbines • Nuclear

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