MAGNETIC ATTRACTION

Spring 2008

The Nature of Magnetism

•Magnets are found everywhere…doorbells, TV’s, computers…

•Magnets were discovered in a region in Greece called….you guessed it…Magnesia!!!

•They discovered the unusual rock about 2,000 years ago.

The Nature of Magnetism…

•The rock had strange properties…• It attracted anything that contained

iron. This rock is the mineral we call magnetite.

•Magnetism is defined as the attraction of a magnet to another object.

•About 1,000 years ago…people discovered that magnets have another unusual property…

The Nature of Magnetism

•If you swing a rock freely from a string…one part of the rock always points in the same direction…toward a specific star…northern star (also called the lodestar).

•For this reason…magnetic rocks are sometimes called lodestones.

Magnetic Poles

• Any magnet has 2 ends – each is a magnetic pole.

• This is the area where the magnetic effect is the strongest…just like one end of a magnetite rock always points on direction…

• One pole will always point north and therefore it is called the north pole. The other is, of course, the south pole.

• The north and south pole are direct opposites.

Attraction...

• What happens when you bring 2 magnets together?

• If you bring the 2 north poles together – they repel or push away from each other. The same is true for 2 south poles.

• If you bring one north and one south pole together – they are attracted to each other.

• So…alike poles repel…unlike poles attract.• Any material that exerts a magnetic

attraction is considered a magnet.

So What’s the Big Deal??

• The Maglev Train…magnetically levitating train…

• Runs solely on magnetism…

• Fast, efficient, and does NOT harm the environment…

What happens if???

• What happens if you break a magnet? • Do you get one south pole and one

north pole magnet?• No…actually… when a magnet is

broken in will develop another pole on that end…so it will always have a north and a south end.

• If you break them again…the same process would happen.

MAGNETO…

• The character Magneto from the “X-Men” comic series has the ability to create magnetic fields and use magnetic force to control objects.

So, What are Magnetic Fields???

• Magnetic forces are exerted all around a magnet, but is strongest at the poles.

• The region of magnetic force around an object is called the magnetic field.

• A magnetic field allows magnets to interact without actually touching.

Magnetic Fields…

• Magnetic field lines map out the magnetic field around an object. These lines spread out from pole to pole and curve around the magnet to return to the other pole. See the diagram at left.

Magnetic Properties…

• Depend on the structure of the atoms making up the object.

• A spinning electron (negatively charged) creates a magnetic field.

• A bar magnet has what is called a magnetic domain. It has a strong representation and therefore a stronger attraction.

• Materials that have a very strong attraction to a magnet are said to be ferromagnetic material. These are items made from iron, nickel, cobalt, samarium, etc.

Creating Magnets…

• You can make a magnet by taking ferromagnetic material and place it in a magnetic field or rub a magnet against it. The field has to be relatively strong for this to occur.

• Once the domains line up – your magnet is created.

• This is why you can magnetize a paperclip to pick up other paperclips.

• Unfortunately, most of theses are only temporary. Permanent magnets are much more difficult to make and hold their magnetism indefinitely

Destroying Magnets…

• You can destroy a magnet field by striking the magnet very hard or dropping it as well.

• This knocks the domains out of alignment.

• Heating a magnet will also destroy the magnetism. Above a certain temperature, materials lose their ferromagnetism properties altogether.

Compass…

• Defined as a device that has a magnetized needle than can spin freely.

• The needle usually points north. • This occurs because the Earth acts like

a giant magnet. Earth has an enormous magnetic field surrounding it – just like a huge bar magnet.

• A scientist named Gilbert believed the center of the Earth contained magnetic rocks…unfortunately, he was wrong, but it was a great start.

More on Compasses…• Scientists now know that

the magnetism is partially caused by the circulation of molten material made from iron and nickel.

• The simple fact that Earth has a magnetic field explains why a compass actually works.

• The magnetized needle aligns its domain with that of the Earth – therefore pointing North.

Magnetosphere…• Earth’s magnetic field

extends into space. • Electrically charged

particles affect Earth’s magnetic field.

• The Van Allen Belts are located about 1,000-25,000 km above the Earth’s surface.

• In this particular region, electrons and protons move at very high speeds.

Magnetosphere…• Solar Winds from the sun

also carry electrically charged particles to Earth.

• The region where Solar Winds shape Earth’s magnetic fields is called the magnetosphere.

• This is a continual process as Earth rotates on it’s axis.

• When the particles move too close to Earth’s surface, we see the Aurora Borealis or Northern Lights in the sky. (called the Southern Lights in the Southern hemisphere…)

Earth’s Magnetic Field…

• Earth’s magnetic directionality has changed throughout history.

• From time to time…the poles will switch due to the magnetic field created by the Earth.

• The last time the poles switched was about 780,000 years ago.

• Scientists are perplexed as to why this occurs, but believe it has something to do with the change in flow of the magnetic molten material at Earth’s core.

It’s Electric!• Electrons carry a negative

charge. Protons carry a positive charge.

• When these charges flow through a wire or other object the create an electric current.

• Electric currents are defined as the flow of a charge through a material.

• The amount of charge that passes through the wire in a unit of time is measured in amperes (an amp).

It’s Electric!

• An electric current produces a magnetic field.

• The direction of the current determines the direction of the magnetic field.

• If the current reverses, so does the field.

Electric Circuits…

• Electric currents do not automatically flow through wires.

• Current only flows through electric circuits.

• An electric circuit is a complete path through which electric charges can flow.

• All electrical devices contain electric currents.

Electric Circuits…• All circuits have the same

basic features.• A circuit has to have a

source of electrical energy.

• Next, circuits have devices that are run by electrical energy…like a light bulb converts electrical energy to electromagnetic energy (it gives off light) and thermal energy (it gives off heat).

• Lastly, electric circuits are connected by conducting wires and a switch.

Conductors…• Electric currents do not

flow through all objects.• Electric currents move

freely through objects called conductors.

• Examples of conductors: copper, silver, iron, and aluminum are all good conductors.

• In a conductor, some of the electrons are only loosely bound to their atoms. These electrons are able to move around and generate an electric current.

Light switch???

• Did you ever wonder why a light comes on when you flip a switch?

• Electrons are not created every time you flip a switch – they are always there in the conductors of the circuit.

Insulators…

• Insulators are a different kind of material where charges are not allowed to move freely.

• The electrons are bound tightly to their atoms and do not flow easily.

• Examples of good insulators: rubber, glass, sand, plastic, and wood.

Electrical Resistance…• A resistor uses electrical

energy as it interferes with, or resists, the flow of charge.

• Resistance is the opposition to the movement of charges flowing through a material.

• Resistance depends on an objects atomic structure. (Like trying to cross a crowded room…the more collisions…the more energy is converted.)

Light Bulb…• Edison used resistance

when developing his light bulb.

• He needed a material that conducted electrical currents, but that would offer enough resistance to make the material heat up and glow.

• He tried a variety of items: copper wires, silk fibers, shredded corn husks to name a few.

• He eventually used the metal tungsten for the purpose.

SUPERCONDUCTORS!!!• A superconductor is a

material that has no electrical resistance.

• This normally occurs at very low temperatures. (That’s the problem!)

• There is no loss of energy and therefore the electrical device is much more efficient.

• They also strongly repel magnets.

• A strong magnetic field would destroy a superconductor.

Electric Motors

• Device that changes electrical energy into mechanical energy.

• All electric motors have an armature – a loop or coil of wire that can rotate.

• Armatures are mounted between the poled of an electromagnet.

• A Commutator reverses the current.

Electricity from Magnetsim

• Galvanometers - device that measures current– Runs by using an electromagnet

• Hans Christian Oersted discovered that an electric current could make a magnetic field.

• Michael Faraday – first to publish results in great detail.

• Electromagnetic induction – electric current is made by changing a magnetic field.

Electric Current continued…

• An electric current is created when a magnet moves in a coil of wire or when a wire moves between the poles of a magnet.

• Electric Generators – uses electromagnetic induction to change mechanical energy into electrical energy.

• Electric generators generate alternating currents.

• Transformers – increases or decreases voltage of an alternating current.

Electromagnets…• Solenoids is a current

carrying wire with many loops.

• The solenoid creates a magnetic field at the center of the coil.

• The 2 ends act like poles and can be turned off or on by a switch.

• If you place a ferromagnetic material inside a solenoid – the magnetic field is increased.

• A solenoid with a ferromagnetic core is called an Electromagnet!

Electromagnets…• Electromagnets are strong

magnets that can be turned off or on.

• These are ideal for lifting large pieces of scrap metal like at a junk yard.

• When the switch is on – the magnet is activated. When the switch is turned off – the magnet is no longer magnetized.

• You can increase and decrease the power of the electromagnet by increasing or decreasing the number of coils of the solenoid or by using a stronger ferromagnetic material.

FINITO!!

That’s All Folks!!