Magnetism & Electromagnetism

1. Magnetism & Electromagnetism

2. Magnets • A special stone first discovered <2000 years ago in Greece, in a region called “Magnesia”, attracted iron, they called it “magnetite” hence the “magnet” name. • 2. About 1000 years ago they noticed that a hanging magnet always pointed to the North Star A.K.A “Lodestar”. Hence the other name for naturally occurring magnets – “lodestone”

3. Magnetic Poles • Magnetic Poles– the ends of the magnet, area where the magnetic effect is the strongest. • If a bar magnet is suspended by a thread or string, it will align itself so that one strong end points north and the other points south, hence the names for the “North” and “South” poles of the magnet. • Like poles of separate magnets repel– push away from – each other • Unlike poles attract each other

4. Magnets • If you snap a magnet in half, the inside pieces become the opposite poles:

5. Magnetic Fields • that region around a magnet that is affected by the magnet. Strongest at the poles, the Force forms lines that go out of the North Pole and wrap back around to enter in at the South Pole.

6. Attract & Repel • Magnets attract because force comes out of North Pole and goes into the South Pole Attraction Repulsion • Magnets repel because the forces are pushing away from each other

7. Inside a Magnet • At the atomic level, there are protons (+ charge) & neutrons (neutral charge) in the nucleus, and electrons (- charge) spinning in orbits around the nucleus. The moving electron acts as a mini electrical charge and therefore has a magnetic field associated w/ it. • In ferrous materials clusters of atoms align there atoms w/ one another. A cluster of billions of atoms w/ magnetic fields aligned is called a domain.

8. Inside a Magnet • When domains are randomly arranged – forces cancel each other out. – no net magnetic affect • When domains have their magnetic affect in alignment - forces are additive and create a strong magnetic affect

9. Making Magnets • Since Magnetism and electricity are so closely related, it is relatively easy to make magnets • Temporary magnets– materials that become magnetized while in contact w/ strong magnets – ie a paperclip is able to pick up more paper clips when stuck to a strong magnet • Permanent magnets– materials that maintain their magnetism when the magnet is removed from it.

10. Electric Current & Magnetic Fields • When electric charges run thru a wire they create an electric current – a flow of charge thru a material • An electric current produces a magnetic field • An electric current through a coil of wire around a nail produces a magnet • Electric circuit – a complete path through which electric current can flow • Each circuit has a source of electrical energy • Have devices that are run by the electric current • Connected by conducting wires and a switch

11. Conductors & Insulators • Conductors allow current to flow easily • Their electrons are loosely bound to their atoms • Metals – copper, silver, iron, superconductors • Insulator – do not allow current to flow easily • Electrons are tightly bound to atom • Plastic, wood, rubber, sand, glass

12. Magnetic Earth • Earth’s core is Iron – Earth is a giant magnet • Earth’s magnetic north pole is not the same as Earth’s axis north pole. It is about 1250 km (776 miles) away from the true north pole • The angle between true north and magnetic north is the magnetic declination.

13. Magnet Lab (22.1) Part 1: Hold two magnets 1 cm apart, push together and record results, repeat for all combinations N-S, N-N, S-S (3 total trials) Part 2:Using a meter stick, slowly bring two magnets together in all three combinations as part 1 and record to the nearest .5 mm the distance that the other magnet moves (either direction). Repeat each trial 3 times. (9 total trials) Part 3: Place 5 magnets together, figure out north and south poles, place your paper over and draw the projected magnetic field lines. Then slowly pour out iron filings over the paper. Comment on what was wrong and correct about your drawing. (Slowly pour iron filings back into container) CLEAN UP! Part 4: Attach a battery to the electromagnetic setup. Count how many paperclips you can attach. Repeat with nail-wire electromagnet, then explain the difference.

14. Electric Currents Produce Magnetism (and vice versa) • Magnetic field around long straight wire Right hand rule determines direction of magnetic field I

15. Right Hand Rule(s) • Long Straight Wire (Rule #1) • Point thumb in direction of current • Fingers wrapped around wire point in direction of magnetic field • Circular loop of Wire (Rule #2) • Curl fingers around wire with tips in field direction • Thumb points in direction of current

16. Alternate (preferred) version of Second RHR • Put curled fingers in current direction around loop or loops; thumb points in field direction INSIDE loop or coil.

17. Force on Current Carrying Wire F = BIL sinQ • is angle between field and wire I q Force is perpendicular to both current and field direction