Chapter 19 Chapter 19 Magnetism and Magnetism and

ElectromagnetismElectromagnetism

Magnets (Magnets (19.119.1))►Magnets contain a mineral called Magnets contain a mineral called

““magnetitemagnetite” also called “lodestones”” also called “lodestones”►Magnetism= the Magnetism= the attractionattraction of a of a

magnet for another objectmagnet for another object►Any shaped magnet has Any shaped magnet has two endstwo ends

that are each called a that are each called a magnetic polemagnetic pole One pole will always point northOne pole will always point north One pole will always point southOne pole will always point south

Interactions between magnetic poles

►Magnetic poles that are alike REPEL each other and magnetic poles that are unlike ATTRACT each

other

►If you break a magnet in half what happens?? Two separate magnets or does it break

into the south pole and north pole…

No, since magnetic field lines are continuous both inside and outside the magnetic you get two north poles and two south poles.

Magnetic FieldsMagnetic Fields►Magnetic Field= the Magnetic Field= the regionregion of of

magnetic magnetic force force around a magnet around a magnet ( allows magnets to interact ( allows magnets to interact without touching)without touching)

►Magnetic Field LinesMagnetic Field Lines= map out the = map out the magnetic field around a magnet. magnetic field around a magnet. *they spread out from one pole, *they spread out from one pole,

curve around a magnet and return to curve around a magnet and return to the other pole (see figure 5 in book)the other pole (see figure 5 in book)

The magnetic field can be seen by placing the magnet under a piece of paper with small iron filings on top. The filings line up in the shape of the field, as shown above.

Inside a magnetInside a magnet►Why do some materials have strong Why do some materials have strong

fields and some don’t?fields and some don’t? The The strength strength depends on thedepends on the spinning spinning and and

orbitingorbiting motion of the electrons ( which motion of the electrons ( which make up lots of tiny magnets) make up lots of tiny magnets)

Magnetic domainMagnetic domain= billions of atoms that = billions of atoms that all have magnetic fields that are lined up all have magnetic fields that are lined up in the same way ( all face north pole at in the same way ( all face north pole at same time… etc.)same time… etc.)

► In a magnetized material In a magnetized material all or mostall or most of the domains are arranged in the of the domains are arranged in the same direction. same direction. They are ALIGNEDThey are ALIGNED

►A material that shows A material that shows strong magneticstrong magnetic effectseffects is said to be a “ferromagnetic is said to be a “ferromagnetic material”material” ““ferrum” ferrum” means means iron iron in Latin in Latin

Making MagnetsMaking Magnets►A magnet can be made from a A magnet can be made from a

ferromagneticferromagnetic material. You can do material. You can do this by placing an unmagnetized this by placing an unmagnetized material in a strong magnetic field or material in a strong magnetic field or by rubbing it with a strong magnet. by rubbing it with a strong magnet.

Example: paper clips can be attracted to Example: paper clips can be attracted to a magnetic material when placed in their a magnetic material when placed in their magnetic fieldmagnetic field

►Permanent magnetPermanent magnet = A magnet made = A magnet made of a material that keeps its magnetism.of a material that keeps its magnetism.

►How do you destroy a magnet??How do you destroy a magnet?? Magnets Magnets loselose their magnetism when their their magnetism when their

domainsdomains become randomly arranged or become randomly arranged or unalignedunaligned. Ways to destroy it…. Ways to destroy it…►1. 1. Drop itDrop it or strike it hard (knocking out of or strike it hard (knocking out of

alignment)alignment)►2. 2. Heat itHeat it to a high temperature (particles to a high temperature (particles

vibrate fast)vibrate fast)

►What happens when you break a What happens when you break a magnet?magnet? When you break a magnet you When you break a magnet you create create

anotheranother magnet magnet with it’s own north and with it’s own north and south pole. south pole.

Magnetic Earth (19.2)Magnetic Earth (19.2)►CompassCompass= a device that has a = a device that has a

magnetized needle that can spin magnetized needle that can spin freely.freely.- Compass needle usually point North.- Compass needle usually point North.

Earth as a magnetEarth as a magnet►The Earth has an immense magnetic The Earth has an immense magnetic

field surrounding it, just as there is a field surrounding it, just as there is a magnetic field around a bar magnet!magnetic field around a bar magnet!

►This is why a compass works- the This is why a compass works- the magnetized needle magnetized needle alignsaligns itself with itself with the Earth’s the Earth’s magnetic fieldmagnetic field

Magnetic declinationMagnetic declination►The The geographicgeographic south and north pole is south and north pole is

different from the different from the magneticmagnetic south and south and north pole- the north pole- the angle between the two angle between the two pointspoints ( geographic and magnetic ( geographic and magnetic poles) is called the poles) is called the magnetic magnetic declinationdeclination * This changes over time because the * This changes over time because the

magnetic poles move slowly!! magnetic poles move slowly!!

MagnetosphereMagnetosphere►Earth’s magnetic field Earth’s magnetic field affectsaffects the the

movements of movements of electrically charge electrically charge particlesparticles in space… and on Earth! in space… and on Earth!

►Van Allen beltsVan Allen belts= Two doughnut = Two doughnut shaped regions above the Earth’s shaped regions above the Earth’s surface. These regions contain surface. These regions contain electronselectrons and and protons protons traveling very traveling very fast. Not dangerous to us! fast. Not dangerous to us!

►Solar windSolar wind= a stream of electrically = a stream of electrically charged particles flowing at high charged particles flowing at high speeds from the sun. The solar wind speeds from the sun. The solar wind helps to helps to shapeshape the Earth’s the Earth’s magnetospheremagnetosphere The magnetosphere is constantly The magnetosphere is constantly

changing due to solar wind! changing due to solar wind!

Effect of Earth’s magnetic Effect of Earth’s magnetic fieldsfields

►Because the Earth produces strong Because the Earth produces strong magnetic fields… it can also magnetic fields… it can also make make magnetsmagnets!!

►-Causes domains to line up in the same -Causes domains to line up in the same directiondirection

►Earth’s magnetic field also Earth’s magnetic field also acts on rocksacts on rocks that that contain magnetic materialcontain magnetic material– creating – creating a permanent record when the molten a permanent record when the molten rock hardens. rock hardens.

Electric Current and magnetic Electric Current and magnetic fields (19.3)fields (19.3)

►Electric charge- electrons are Electric charge- electrons are negatively negatively chargedcharged(-) (-) and and protonsprotons are are positivelypositively charged (+)charged (+)

►Electric currentElectric current= the flow of charge = the flow of charge through a material. The amount of charge through a material. The amount of charge is is measuredmeasured in the in the ampere or amp or Aampere or amp or A The number of amps tells the The number of amps tells the amount of amount of

chargecharge flowing past a given point flowing past a given point each secondeach second

►**An electric current produces a **An electric current produces a magnetic field!!magnetic field!!

►Moving charge and magnetismMoving charge and magnetism

All magnetism is caused by the movement All magnetism is caused by the movement of charges. of charges.

Electric circuitsElectric circuits►Electric CircuitElectric Circuit= a complete path through = a complete path through

which electric charges can flow. which electric charges can flow. Current ONLY flows through an electric circuit! Current ONLY flows through an electric circuit! A circuit needs A circuit needs threethree things.. things.. 1. a 1. a sourcesource of of electricalelectrical energy energy 2. 2. devices devices that are that are runrun by electrical energy by electrical energy

( ex. Radio, computer, light bulb)( ex. Radio, computer, light bulb) 3. 3. connectedconnected by by conductingconducting wires and a wires and a switchswitch

Conductors and InsulatorsConductors and Insulators►ConductorConductor= electric currents flow = electric currents flow

freely through these materials and are freely through these materials and are loosely bound to their atoms loosely bound to their atoms

( ex. Copper, silver, iron, and ( ex. Copper, silver, iron, and aluminum)aluminum)

InsulatorInsulator= a different kind of = a different kind of material in which charges are material in which charges are not able to move freely and not able to move freely and the atoms are bound tightly the atoms are bound tightly together!together!

Electrical ResistanceElectrical Resistance►ResistorResistor= uses electrical energy as it = uses electrical energy as it

interferes with or interferes with or resists the flow of resists the flow of chargecharge

►ResistanceResistance= the = the oppositionopposition to the to the movement of charges flowing through a movement of charges flowing through a materialmaterial Resistance of the material depends on its Resistance of the material depends on its

atomic structureatomic structure ( close together vs. spread ( close together vs. spread out)out)

►Thomas Edison used Thomas Edison used resistance (current) when resistance (current) when he developed the electric he developed the electric light bulb- he used light bulb- he used Tungsten because it can Tungsten because it can get hot enough to glow get hot enough to glow without melting! without melting!

►SuperconductorSuperconductor= a material that has = a material that has no electrical resistance- this means no electrical resistance- this means that there is NO loss of energy!that there is NO loss of energy! Very low temperatures are required for a Very low temperatures are required for a

superconductorsuperconductorWhy would using superconductors reduce Why would using superconductors reduce

wasted energy?? wasted energy??

ElectromagnetsElectromagnets►SolenoidsSolenoids= A current carrying coil of = A current carrying coil of

wire with many loops, A solenoid wire with many loops, A solenoid creates a magnetic field that can be creates a magnetic field that can be turned off and on by switching the turned off and on by switching the current off and on! current off and on! The north and south poles change with The north and south poles change with

the direction of the currentthe direction of the current

Multiplying MagnetismMultiplying Magnetism►A solenoid with an ferromagnetic core A solenoid with an ferromagnetic core

is called an is called an ElectromagnetElectromagnet The temporary field of an electromagnet The temporary field of an electromagnet

is produced by the current in the wire and is produced by the current in the wire and the magnetized corethe magnetized core

An electromagnet is a strong magnet that An electromagnet is a strong magnet that can be turned off and oncan be turned off and on

►How do you increase the strength of How do you increase the strength of an electromagnet? an electromagnet? 1. 1. IncreaseIncrease the the currentcurrent in the solenoidin the solenoid 2. 2. AddAdd more loops of more loops of wire wire to the solenoidto the solenoid 3. 3. WindWind the the coilscoils around the solenoid around the solenoid

closer togethercloser together 4. Using a 4. Using a stronger ferromagnetic corestronger ferromagnetic core

Recording InformationRecording Information►Electromagnets are used to Electromagnets are used to record record

informationinformation onto audiotapes, onto audiotapes, videotapes, computer disks and credit videotapes, computer disks and credit cardscards Magnetized particles are put into a Magnetized particles are put into a

patternpattern that can later be that can later be translated translated into into information/sound/video.information/sound/video.