Good morning!

1. Good morning! You will need: Worksheet by the door

2. History of Magnets • More than 2000 years ago, rocks called lodestones were found in the region of Magnesia in Greece. • In the 12th century, the Chinese used them for navigating ships.

3. What are magnets? • Most materials • Have paired up electrons moving in opposite directions. • The field created by one moving charge is canceled by the other. • No magnetic field is created.

4. What are magnets? • Any charges in motion produce a magnetic field. • Some materials like Iron, Nickel, or Cobalt • Have a single electron or paired electrons spinning in the same directions. • The magnetic field created by one electron is not canceled by the other. • An atomic sized magnet is created.

5. As in electromagnetic waves, when an a charge moves it creates a magnetic and electric field at right angles.

6. Why is Fe magnetic and Al not? • What makes a good magnet? • Every spinning electron is a tiny magnet. • A pair of electrons spinning in the same direction is a stronger magnet. • A pair of electrons spinning in opposite directions work against one another; the magnetic fields cancel. • Fe has two unpaired electrons spinning in the same direction. • Cobalt has 3. • Nickel has 4. • Aluminum has one unpaired electron.

7. Magnetic Poles • All magnets have two regions “poles” that produce magnetic forces. • They are named like this because if you take a magnet and suspend it from the middle (so that it can swing freely), it will rotate until the north pole of the magnet points north and the south pole points south. • Like poles repel. • Opposite poles attract.

8. No less than two. • North and South cannot be separated. • If a magnet is broken, poles aren’t separated; two smaller magnets are formed.

9. Magnetic Domains • In magnetic materials, neighboring atoms pair up to form large groups of atoms whose net spins are aligned. • These groups are called domains. • When a piece of iron is not a magnet, the domains point in random directions.

10. Magnetic Domains • If the non-magnetized iron is placed in a strong magnetic field, the domains will line up in the direction of the field. • In temporary magnets, the domains will return to their random orientation after the field is removed. • In permanent magnets, the domains will remain aligned. • 1 domain = 1 quadrillion (1015) atoms

11. Magnetic Fields • You have probably noticed that forces between the magnets (both attraction and repulsion), are felt not only when the magnets are touching each other, but also when they are held apart. • In the same way that gravity can be described by a gravitational field, magnetic forces can be described by the magnetic fields around magnets.

13. Magnetic Field Demo • What kinds of magnetic fields are produced by pairs of bar magnets?

14. MagneticField Lines The shape of the magnetic field. If you place a compass in the field its arrow will point parallel to the field lines.

15. Magnetic Field Lines • Magnetic field lines are the same as electric field lines in that both are stronger when lines are drawn closer together. • So the magnetic field is stronger at the poles • The magnetic field lines have arrows going from north to south. • Magnetic field lines do not cross because the magnetic field cannot go in two directions at once.

16. Temporary Magnets • What happens when you place a magnet next to a nail? • This is because the magnet causes the nail to become polarized; the nail becomes a magnet. • Aluminum and lead are not a magnetic. • This is temporary; if you pull the magnet away, the nail loses its magnetism.

17. Permanent Magnets • Permanent magnets are produced in the same manner as the nail; however, due to the microscopic structure of the material, the magnetism becomes more permanent. • Most permanent magnets are made of ALNICO, an iron alloy containing 8% Aluminum, 14% Nickel, and 3% Cobalt. altho. Al is not a magnet • Some rare earth elements, such as neodymium and gadolinium, produce strong permanent magnets.

18. Common Uses of Magnets • Magnetic recording media: VHS tapes, audio cassettes, floppy disks, hard disks. • Credit, debit, and ATM cards • Common television and computer monitors • Speakers and Microphones • Electric motors and generators • Compasses • Magnets can pick up magnetic items (iron nails, staples, tacks, paper clips) that are either too small, too hard to reach, or too thin for fingers to hold. Some screwdrivers are magnetized for this purpose. • Magnets can be used in scrap and salvage operations to separate magnetic metals (iron, steel, and nickel) from non-magnetic metals (aluminum, non-ferrous alloys, etc.). • Magnetic levitation transport, or maglev, is a form of transportation that suspends, guides and propels vehicles (especially trains). The maximum recorded speed of a maglev train is 361 mph.

19. How to demagnetize a magnet • Heating a magnet past its Curie temperature - the molecular motion destroys the alignment of the magnetic domains. • 768°C for Iron • Hammering or jarring – the mechanical disturbance tends to randomize the magnetic domains. • Placing the magnet in an alternating magnetic field.

20. Ferrofluid • a mixture of tiny iron particles covered with a liquid coating that are then added to water or oil. • Used in car suspensions, cancer detection, loud speakers • video

21. Ferrofluid in Acura

22. Earth’s Magnetic Field • Earth is a huge magnet. • This is possibly due to the molten Iron core. • The magnetic field around Earth is called the Magnetosphere

23. Earth’s Magnetic Field • Magnetic north pole is different than geographical north pole. • There is about a 25 ̊difference from geographic north pole to magnetic north pole, this is called magnetic declination • In addition, the north pole of a magnet is attracted to earth’s north pole because that is the magnetic south pole. • The south pole of a magnet is attracted to the earth’s south pole because that is the magnetic north pole.

24. Magnetosphere • Extends several tens of thousands of km into space. • Protects Earth from solar winds.

26. Auroras • Charged particles from the sun become trapped in Earth’s magnetic field. • This occurs near the magnetic poles. • These charged particles collide with electrons of the atoms in our atmosphere and transfer their energy. • The colors of the lights are determined by the type of gases in the atmosphere. • O2 releases green light; N2 releases red light • aurora borealis (northern lights); aurora australis (southern lights)

27. Dynamo Theory • The dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. • In the case of the Earth, the magnetic field is induced and constantly maintained by the convection of liquid iron in the outer core.

28. Magnetic field of Earth is not stable • The magnetic poles of Earth wander up to 15 km every year. • Based upon the study of lava flows throughout the world, Earth's magnetic field reverses at intervals, ranging from tens of thousands to many millions of years, with an average interval of approximately 250,000 years. • The last reversal is theorized to have occurred 780,000 years ago.

29. Other Planets’ Magnetic Fields • The sun also has a strong magnetic field. Evidence seen in sun spots. • They occur in pairs. • They also peak at an 11-year cycle, which coincides with the flipping of the sun’s magnetic field. • Jupiter’s magnetic field is 10 times the strength of Earth’s. • The moon has no magnetic core, and hence, no magnetic field.

30. Neutron Stars • The most intense magnetic field ever found in the universe has been observed around a neutron star 40,000 light years from Earth. • Neutron stars are compact objects that are created during supernova explosions. • The magnetic field of a Neutron Star is estimated to be one thousand trillion times the strength of Earth's magnetic field.

31. Animal Migration • Some animal species do have the ability to detect the magnetic field, & they use it to make their migrations. • Bats and sea turtles use magnetic information to find their way. • We're not 100 percent sure how animals detect the magnetic field, but small particles of magnetite have been found in the brains of some species. Those particles may be reacting to the magnetic field and activating nerves in such a way as to send orientation information to the animal's brain.

32. Bacteria & Magnets • Some bacteria have a chain of magnetite as part of their internal structure • They use this magnetite to find their way in swamps • Bacteria in the northern hemisphere have magnetite that are opposite in polarity than the bacteria with magnetite in the southern hemisphere.

33. Animal Migration Video

34. Moving Charges A moving charge produces a magnetic field. Many charges in motion – an electric current – also produce a magnetic field. This was discovered in 1820 by Hans Oersted. He ran an electric current through a wire and positioned compasses around the wire.

35. As in electromagnetic waves, when an a charge moves it creates a magnetic and electric field at right angles.

36. Electromagnetism • Oersted discovered that a magnetic field can be formed from a current, now we will learn how a current can be formed from a magnetic field • When Michael Faraday made his discovery of electromagnetic induction in 1831, he discovered that a changing magnetic field is necessary to induce a current in a nearby circuit.

37. Creating Current • Faraday discovered that if a wire is moved in a magnetic field, a voltage is produced, and if there is a complete loop, a current will flow. This is how electricity is generated. • This is electromagneticinduction

38. Generating electricity In industry, electricity is generated by spinning a coil of wire in a magnetic field. To increase the voltage or current generated: • Spin the coil faster. • Put more loops on the coil. • Use a stronger magnetic field. • Use a coil with a larger area.

39. It’s all related. • So Oersted discovered that currents produce magnetic fields, and 11 years later, Faraday discovered induction. • In the 1860s, Maxwell predicted that even without wires, changing electric fields produce magnetic fields, and changing magnetic fields produce electric fields. • The result of this was the discovery that energy transmitted across empty space is in the form of electromagnetic waves.

40. Why the loops? • By bending the wire into a loop, the magnetic field lines are bunched up inside the loop. • If you add more loops, the magnetic field will become stronger. • Two loops = magnetic field is doubled. • Three loops = magnetic field is tripled. • Electromagnet – a current carrying wire with many loops.

41. Add a core to the electromagnet • If a piece of iron is placed inside the coil of the electromagnet, the domains of the piece of iron are forced into alignment, increasing the intensity of the magnetic field. • Electromagnets are strong temporary magnets – they can be turned on and off easily.

42. Making an electro magnet in class. A magnet you can turn on and off when you regulate the power in the wire.

43. Applications of Induction • Generators • A generator is nothing more than the reverse of an electric motor • A motor, you put current (battery) into it , electrical energy, and you get mechanical work out of it (spinning our wire)  • A generator, you put mechanical work into it (water running, or falling, steam, etc.) and you get current out • Microphone • A simple microphone is the reverse (symmetry) of a speaker.  • A speaker, you put alternating current into it and you get sound out.  • A microphone, you put sound into and you get alternating current out.

47. Speakers • Alexander Graham Bell patented the first electrical loudspeaker as part of his telephone in 1876. • The loudspeakers in most sound systems use magnets to produce sound waves. • One design is a flexible paper cone attached to a coil of wire and a permanent magnet • The current through the wire causes a magnetic force on the coil.

48. Transformers! • Transformers can either step voltage up OR down! • This is the main reason why we use AC circuits! • Notice that the transformer is made with two different wire coils. • The magnetic field of one coil is transferred to the other coil via an iron core. • The difference in coil configuration creates a difference in voltage!

49. The principal reason voltage is induced in the loops of a generator coil is that loops are rotating, and changing the amount of magnetic field within the loops. V/n = V/n

50. Transformers • You see transformers everywhere! • They are those big cylindrical cans you see on power poles • They are those big green metal boxes you see on the side of some buildings that say, “Danger! High Voltage!” • They are in many appliances that require to step up the voltage supplied in our walls (120V) • Because of transformers, AC voltage became the voltage of choice