2 MagnetsA 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 PolesMagnetic 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 otherUnlike poles attract each other
4 MagnetsIf you snap a magnet in half, the inside pieces become the opposite poles:
5 Magnetic Fieldsthat 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 & RepelMagnets attract because force comes out of North Pole and goes into the South PoleAttractionRepulsionMagnets repel because the forces are pushing away from each other
7 Inside a MagnetAt 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 MagnetWhen domains are randomly arranged – forces cancel each other out. – no net magnetic affectWhen domains have their magnetic affect in alignment - forces are additive and create a strong magnetic affect
9 Making MagnetsSince Magnetism and electricity are so closely related, it is relatively easy to make magnetsTemporary 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 magnetPermanent 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 materialAn electric current produces a magnetic fieldAn electric current through a coil of wire around a nail produces a magnetElectric circuit – a complete path through which electric current can flowEach circuit has a source of electrical energyHave devices that are run by the electric currentConnected by conducting wires and a switch
11 Conductors & Insulators Conductors allow current to flow easilyTheir electrons are loosely bound to their atomsMetals – copper, silver, iron, superconductorsInsulator – do not allow current to flow easilyElectrons are tightly bound to atomPlastic, 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 poleThe 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 wireRight hand rule determines direction of magnetic fieldI
15 Right Hand Rule(s) Long Straight Wire (Rule #1) Point thumb in direction of currentFingers wrapped around wire point in direction of magnetic fieldCircular loop of Wire (Rule #2)Curl fingers around wire with tips in field directionThumb 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 sinQis angle betweenfield and wireIqForce is perpendicular to both current and field direction