Magnetism & Magnetism & ElectromagnetismElectromagnetism

MagnetsMagnets A special stone first discovered <2000 years ago in Greece, in A special stone first discovered <2000 years ago in Greece, in

a region called “a region called “MagnesiaMagnesia”, attracted iron, they called it ”, attracted iron, they called it ““magnetitemagnetite” hence the “magnet” name.” hence the “magnet” name.

2. About 1000 years ago they noticed that a hanging magnet 2. About 1000 years ago they noticed that a hanging magnet always pointed to the North Star A.K.A “always pointed to the North Star A.K.A “LodestarLodestar”. Hence ”. Hence the other name for naturally occurring magnets – “the other name for naturally occurring magnets – “lodestonelodestone””

Magnetic PolesMagnetic Poles

Magnetic PolesMagnetic Poles – the ends of the magnet, area where the magnetic effect is – the ends of the magnet, area where the magnetic effect is the the strongeststrongest..

If a bar magnet is suspended by a thread or string, it will align itself so that 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 one strong end points north and the other points south, hence the names for the “North” and “South” poles of the magnet.the “North” and “South” poles of the magnet.

Like poles of separate magnets repel – push away from – each other Unlike poles attract each other

MagnetsMagnets

If you snap a magnet in half, the inside pieces become the opposite poles:

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.

Attract & RepelAttract & Repel Magnets attract because force comes out of North Pole and

goes into the South Pole

Magnets repel because the forces are pushing away from each other

Attraction Repulsion

Inside a MagnetInside 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.

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

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.

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

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

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.

Magnet Lab (22.1)Magnet Lab (22.1)Part 1: Hold two magnets 1 cm apart, push together and record 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)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 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 all three combinations as part 1 and record to the nearest .5 mm the distance that the other magnet moves (either direction). the distance that the other magnet moves (either direction). Repeat each trial 3 times. (9 total trials)Repeat each trial 3 times. (9 total trials)

Part 3: Place 5 magnets together, figure out north and south poles, Part 3: Place 5 magnets together, figure out north and south poles, place your paper over and draw the projected magnetic field place your paper over and draw the projected magnetic field lines. Then slowly pour out iron filings over the paper. lines. Then slowly pour out iron filings over the paper. Comment on what was wrong and correct about your drawing. Comment on what was wrong and correct about your drawing. (Slowly pour iron filings back into container) CLEAN UP!(Slowly pour iron filings back into container) CLEAN UP!

Part 4: Attach a battery to the electromagnetic setup. Count how Part 4: Attach a battery to the electromagnetic setup. Count how many paperclips you can attach. Repeat with nail-wire many paperclips you can attach. Repeat with nail-wire electromagnet, then explain the difference.electromagnet, then explain the difference.

Electric Currents Produce Electric Currents Produce Magnetism (and vice versa)Magnetism (and vice versa)

Magnetic field around long straight wireMagnetic field around long straight wire

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Right hand rule determines direction of magnetic field

Right Hand Rule(s)Right Hand Rule(s)

Long Straight Wire (Rule #1)Long Straight Wire (Rule #1) Point thumb in direction of currentPoint thumb in direction of current Fingers wrapped around wire point in direction of Fingers wrapped around wire point in direction of

magnetic fieldmagnetic field Circular loop of Wire (Rule #2)Circular loop of Wire (Rule #2)

Curl fingers around wire with tips in field directionCurl fingers around wire with tips in field direction Thumb points in direction of currentThumb points in direction of current

Alternate (preferred) version of Alternate (preferred) version of Second RHRSecond RHR

Put curled fingers in current direction around Put curled fingers in current direction around loop or loops; thumb points in field direction loop or loops; thumb points in field direction INSIDE loop or coil.INSIDE loop or coil.

Force on Current Carrying WireForce on Current Carrying Wire

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F = BIL sinF = BIL sin

is angle betweenis angle between

field and wirefield and wire

Force is perpendicular to both current and field direction