Chapter 19 Magnetism and Electromagnetism Magnets 19 1

Chapter 19 Magnetism and Electromagnetism

Magnets (19. 1) ► Magnets contain a mineral called “magnetite” also called “lodestones” ► Magnetism= the attraction of a magnet for another object ► Any shaped magnet has two ends that are each called a magnetic pole § One pole will always point north § One 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 Fields ► Magnetic Field= the region of magnetic force around a magnet ( allows magnets to interact without touching) ► Magnetic Field Lines= map out the magnetic field around a magnet. § *they spread out from one pole, curve around a magnet and return to 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 magnet ► Why do some materials have strong fields and some don’t? § The strength depends on the spinning and orbiting motion of the electrons ( which make up lots of tiny magnets) § Magnetic domain= billions of atoms that all have magnetic fields that are lined up in the same way ( all face north pole at same time… etc. )

a magnetized material all or most of the domains are arranged in the same direction. They are ALIGNED ► In ►A material that shows strong magnetic effects is said to be a “ferromagnetic material” § “ferrum” means iron in Latin

Making Magnets ►A magnet can be made from a ferromagnetic material. You can do this by placing an unmagnetized material in a strong magnetic field or by rubbing it with a strong magnet. § Example: paper clips can be attracted to a magnetic material when placed in their magnetic field

► Permanent magnet = A magnet made of a material that keeps its magnetism. ► How do you destroy a magnet? ? § Magnets lose their magnetism when their domains become randomly arranged or unaligned. Ways to destroy it… ► 1. Drop it or strike it hard (knocking out of alignment) ► 2. Heat it to a high temperature (particles vibrate fast)

► What happens when you break a magnet? § When you break a magnet you create another magnet with it’s own north and south pole.

Magnetic Earth (19. 2) ► Compass= a device that has a magnetized needle that can spin freely. - Compass needle usually point North.

Earth as a magnet ► The Earth has an immense magnetic field surrounding it, just as there is a magnetic field around a bar magnet! ► This is why a compass works- the magnetized needle aligns itself with the Earth’s magnetic field

► Solar wind= a stream of electrically charged particles flowing at high speeds from the sun. The solar wind helps to shape the Earth’s magnetosphere § The magnetosphere is constantly changing due to solar wind!

Effect of Earth’s magnetic fields ► Because the Earth produces strong magnetic fields… it can also make magnets! ► -Causes domains to line up in the same direction ► Earth’s magnetic field also acts on rocks that contain magnetic material– creating a permanent record when the molten rock hardens.

Electric Current and magnetic fields (19. 3) ► Electric charge- electrons are negatively charged(-) and protons are positively charged (+) ► Electric current= the flow of charge through a material. The amount of charge is measured in the ampere or amp or A § The number of amps tells the amount of charge flowing past a given point each second

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

► Moving charge and magnetism § All magnetism is caused by the movement of charges.

Electric circuits ► Electric Circuit= a complete path through which electric charges can flow. § Current ONLY flows through an electric circuit! § A circuit needs three things. . § 1. a source of electrical energy § 2. devices that are run by electrical energy ( ex. Radio, computer, light bulb) § 3. connected by conducting wires and a switch

Conductors and Insulators ► Conductor= electric currents flow freely through these materials and are loosely bound to their atoms ( ex. Copper, silver, iron, and aluminum)

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

Electrical Resistance ► Resistor= uses electrical energy as it interferes with or resists the flow of charge ► Resistance= the opposition to the movement of charges flowing through a material § Resistance of the material depends on its atomic structure ( close together vs. spread out)

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

► Superconductor= a material that has no electrical resistance- this means that there is NO loss of energy! § Very low temperatures are required for a superconductor Why would using superconductors reduce wasted energy? ?

Electromagnets ► Solenoids= A current carrying coil of wire with many loops, A solenoid creates a magnetic field that can be turned off and on by switching the current off and on! § The north and south poles change with the direction of the current

Multiplying Magnetism ►A solenoid with an ferromagnetic core is called an Electromagnet § The temporary field of an electromagnet is produced by the current in the wire and the magnetized core § An electromagnet is a strong magnet that can be turned off and on

► How do you increase the strength of an electromagnet? § 1. Increase the current in the solenoid § 2. Add more loops of wire to the solenoid § 3. Wind the coils around the solenoid closer together § 4. Using a stronger ferromagnetic core

Recording Information ► Electromagnets are used to record information onto audiotapes, videotapes, computer disks and credit cards § Magnetized particles are put into a pattern that can later be translated into information/sound/video.