Question of the Day:

1. Question of the Day: Sketch the magnetic (B) field around a bar magnet. C F B A S N D E Which way will the north pole of a compass point if placed at point A-F? What is the direction of the B-field at A-F?

2. A compass works just like iron filings:

3. What do these have in common?

4. north and south pole II. All magnets have a ___________________________. S N If you break a magnet… S N will become an entire magnet …each piece ________________________________: N S N S If you break it again, each piece will _____________ _____________________. A separate, single, N or S magnetic pole (called a ________________ ) has _____________________________ . again have both a N- and S-pole monopole never been observed

5. Earth has a magnetic field that is __________________ the field of ______________________. similar to a bar magnet magnetic ______________ axis true ________ axis S bar magnet _________ _________ Earth N _________ Earth’s B field: --protects the planet from ______________________ --produces the _________________________________ --at the surface is a result of the magnetic effects of: a/ __________________________________________ b/ __________________________________________ c/ __________________________________________ d/ ___________________________________________ - cosmic rays borealis (northern) lights rotating currents in the outer core (90%) magnetic rocks in the crust electric currents in the ionosphere ocean currents

8. The magnetosphere—a magnetic “cocoon”:

9. The Origin of the __________________________ : Charged particles from the Sun experience a ________________ force that is _________________ to their ______________ and to the ____________ field. This is a ________________ force Fc that causes them to _____________ around the B field. As they spiral down to Earth, they knock ___________ out of atmospheric ________ . When these electrons _______________ with their atoms, they ___________________________ . aurora borealis path of a _________ particle magnetic charged perpendicular velocity magnetic centripetal spiral electrons Fc ____ due to B field atoms re-combine B field _______ line emit light of different colors

13. Earth's field makes an angle to its surface called the _________________________. inclination What is the angle at the poles? What is the angle at the equator? 900 00

14. How to measure the inclination of Earth's B? Compass and dip needles were used to find magnetite in Sweden in the Middle Ages, making the magnetic method the oldest of all applied geophysical techniques. This method of magnetic prospecting for ores was used extensively for iron mining up until the early decades of the twentieth century. However, the dip circle is not a sensitive enough instrument for most ore prospecting purposes and has been replaced with ground-based versions of magnetometers used in aeromagnetic surveys. magnetized steel needle 18 cm

15. The N- and S-poles of Earth’s B field: • a/ are not the same as the __________ (true) poles • b/ _____________________________ • c/ Sometimes ____________ polarity so that • ____________________ and vice versa. The last • time this occurred was about ____________ y ago spin slowly wander around reverse N becomes S 750,000 Magnetic ___________________ is the angle that the _______________ north makes with _________ north. declination true magnetic 130 In Ilion, the declination is about ___________ magnetic true ________ north __________ north 130 W

16. magnetic N pole The wandering _______________________ 130 New York _______________

17. Magnetic declination changes… …in space:

18. …and in time.

20. Neutron stars are large stars that have collapsed until they are planet sized. As they collapse, their magnetic fields intensify. As they rapidly rotate, their magnetic field sweeps around like a lighthouse. They were originally called pulsars.

21. The Sun’s magnetic field… • produces sunspots • reverses itself every 11 y • (next peak: 2012….) • 3. affects climate on Earth.

22. magnetograms of the sun: dark is one pole, light is the other

23. In 2012: • A comet may strike Earth. • Yellowstone Caldera may erupt. • The Mayan Calendar predicts the End of the World. • The magnetic field of Earth may reverse • The sunspot cycle will reach its peak. • Which one of these facts is an inference most likely • to come true?

24. Magnet therapy:

25. __________________experiment (1819 in Copenhagen): Oersted’s wire N S compass switch battery An electric current ___________________________.  Currents, I, _____________________________. ________________ and Magnetism are closely related. Each one can induce (give rise to) the other. This is the basis for the ______________________ generation of power . deflected the compass cause magnetism, B Electricity electromagnetic

26. I. The Magnetic Fields of Current-Carrying wires: wire Experiment: Hang a _______ vertically. Support a piece of paper horizontally. Turn _____________. Sprinkle iron filings to see the ______________ pattern. current on B field right hand The _____________ rule tells you which one of the two possible ways that the B field points. nice animation

27. I > The B field of a long straight wire has the shape of _________________________ . concentric circles View directly at wire with I towards you: I > B B B side view:

28. coil Ex: Twist a wire into the shape of a _______. coil I The B field of the coil is shaped like a _______________: Side view: bar magnet N N S S

30. Electromagnets • _______________________ are magnets made with coils. • They are also called ____________________ . • To strengthen its B field, use: • _______________________ • ______________________ • __________________________ solenoids more current more coils a ferromagnetic core Fe C o r e

31. What are electromagnets used for? Plus electric motors and generators…

32. The B field of the electromagnet turns its iron core into a magnet. The core will then be attracted into the coil's field.  This is how solenoids work.

33. Analog ammeters (and voltmeters) use coils, too: • Current is used in coils to create electromagnets. • The electromagnets repel/attract and move the needle. • The stronger the current, the more the force, and • the more the needle moves.

35. II. Magnetism in Solids. Magnetism in solids is caused by the ______________ that result from the motion of ________________ as they 1/ _____________________________ , or 2/ _____________________________ within each atom. currents electrons "spin" on their axis "orbit" their nuclei An atom: e- spins on axis nucleus e- orbit Think of a spinning electron: as a tiny _______ ___________: S bar magnet N

36. Isn't it amazing that Earth's magnetic field is similar to that of an electron!!!!

37. Types of magnetism: • ferromagnetism: • --___________________ attraction • --only in ______________________ • --caused by ___________________electrons that • act _______________________ strong Fe, Ni and Co unpaired cooperatively Why ferromagnetism only occurs in certain atoms: Electrons can only "fit" in certain _______________ around the nucleus called _______________ . At most, only ___ electrons, spinning in ________________ directions, can fit in each _______________ . positions 2 orbitals opposite orbital orbital = represents an electron ______________ in an atom one way = represents an e- spinning ______________ the other way = represents an e- spinning ______________

38. unique Each element has its own ______________ arrangement of orbitals and ______________ of electrons. Whether an atom is ferromagnetic or not depends on whether the ________________ are _______________ or not. number filled up orbitals not magnetic cancel filled = ________ orbital  spins ________  _____________ ferromagnetic because spins act like magnets unfilled = _________ orbital  __________________________  __________________________ • diamagnetism: • --weak magnetic ________________ • --occurs in water, glass, Cu, Pb, salt, wood, • most gases, plastics, etc. repulsion • paramagnetism: • --weak magnetic _________________ • --Al, O, Na attraction

39. In a ferromagnetic solid (iron, nickel or cobalt), atoms with unfilled electron orbitals organize themselves into domains -- area in which the electrons are lined up Ex. An unmagnetized ferromagnetic material has random domains: = spin of an electron domains Ex. A magnetized ferromagnetic material has domains that are aligned with each other external magnetic field

40. 4. Human magnetism: Franz Mesmer (mesmerized…)

41. Ex. Credit cards have a magnetic strip that records information: Don’t do this!

42. What kind of field surrounds … caused by: Field mass m gravitational g 1. a neutron at rest? gravitational g mass m • a proton or an • electron at rest? electric E charge q gravitational g electric E magnetic B mass m • a moving* proton • or electron? charge q current I "relative" *The motion is _________________ . This means that you will also measure a B if the charge is __________ and you _________________ . at rest past it

43. Uses of strong magnetic fields: • _______________________________________ • ______________________________________ • _______________________________________ • ______________________________________ • _____________________________________ • To produce strong magnetic fields, • ___________________ are needed. But this causes • ______________ or ___________ heating. To reduce • the heating, ____________________________ are used • because they have no __________________________. medical - NMRs power transmission transportation – maglev trains computer memory research – contain fusion reactions high currents I2R joule superconductors resistance