Warm Up: Create a hypothesis for the following question: Where does magnetism come from? (here, I’ll give you a hint, it involves the last couple of chapters we have been discussing)

MAGNETISM

Objectives & Key Questions Objectives: -Learn about the origins of magnetism -Discuss the relationship between magnetism and electricity Key Questions: -Where does magnetism come from? -How does magnetism effect your everyday life? -What are some practical uses of magnets? -What’s the deal with this whole Earth magnet thingy?!

Misconceptions  By breaking a magnet in two, you will isolate a north pole or a south pole  The Earth’s magnetic field is very strong  Like in movies, magnetism can pull things constantly from a far distance (Think of the movie “Wild Wild West”)

A Brief History Magnetism Magnetism was discovered in “Lodestones”: Natural magnets found in Magnesia, Greece. Often the subject of curiosity and eventually were used as devices for navigation.

A Brief History of Magnetism Charles Coulomb (Yes, that same guy who stole Newton’s Law!!!) studied lodestones and the forces between them -They contain pieces of “iron ore” called magnetite Hans Christian Oersted was the first man to discover the relationship between magnetism and electric current.

Question What are the similarities and differences between magnetism and electric charges?

Strength of a Magnet What effects the strength of a magnet? Try holding the bar closer and closer to the magnet with out letting it touch, what do you notice about the strength of a magnet, as you get closer? What is this similar to?  As distance increases, field strength decreases (Inverse Square!!).  As pole strength increases, field strength increases.

Poles What do we already know about poles? Has the word come up already?

Magnetic Poles Every magnet has a north and a south pole How are poles similar to electric charges?  Like poles repel  Unlike poles attract But how are they different?

Breaking a magnet What will happen if you break a magnet in two? With the two magnets, try attaching different ends of each magnet and record what happens. What do you think will happen if Mr. Stief breaks a magnet and try this again but with the two broken pieces? What happens? What does this say about magnetic poles?

Breaking a magnet  Unlike charges, magnetic poles ALWAYS come in pairs

Origin of magnetism Where does magnetism come from? Magnetism comes from the movement of electric charges. Any time electric charges more, a magnetic field forms. This can be from spinning charges or traveling charges. When an atom has more movement of electrons in one direction then another, you get a net magnetic field. Atoms that have equal amounts of movement in all directions are magnetically neutral.

What have Natural Poles? Metals like iron, nickel and cobalt can be natural magnets –Due to a net number of electrons spinning in the same direction, these metals have natural magnetic dipole moments. –Iron is the strongest So this means that even atoms can be like tiny little magnets.

Magnetic Domains A domain is a cluster of magnetic atoms that have aligned to form a small magnetic dipole (the little arrows on the picture) Domains are like tiny magnets When all of the domains in a material start to point in the same direction… you get a magnet

Field Lines Pour out some iron shavings onto a tray while holding a bar magnet underneath it. What happens to the filings? Draw this: Why does this happen? How is it similar/different to other concepts we have discussed in this class?

Field lines Just like with electric charges, field lines can also be drawn for magnets. A great way to actually see field lines is to use iron filings. Magnetic fields also have direction (just like electric fields). They flow from North to South

Creating a magnet Paper Clips: Try picking up a paper clip by just touching the one in your hand to one on your desk. Does this work? Are paper clips magnets? Paper clip and magnet: Now connect your paper clip to your magnet and try it again. What happens? Why do you think this happens?

Creating Magnets Pennies: Try this again but instead of paper clips, use a couple of pennies. Are pennies magnetic? Make a hypothesis as to why your materials behaved this way. Only some materials are “ferromagnetic (They have many domains and are able to magnetized).” Materials that aren’t ferromagnetic don’t have many/any domains. Copper is not a ferromagnetic material.

1st Method for creating a magnet There are a number of way to align the domains in a material. Based on the paper clip activity, we already know one. 1.By placing non-magnetized metals against or near a magnet, the domains in the non-magnetized material will line up and a net magnetic moment will form:

2nd and 3rd ways 3.One of the best ways is to heat the material (like the magma from the mid-atlantic ridge) and then pass it through a magnetic field. When the material cools, its domains will have settled in an aligned fashion. 2.By rubbing a material with unaligned domains with a magnet, the domains will align themselves, forming a magnet. Permanent Magnet: When the domains in a material are able to stay aligned for a long amount of time. Always keeps its magnetic properties even when it is not near other magnets.

Planets! -Earth, as well as other planets, have natural magnetic fields. -This can be noticed by the fact that for hundreds of years people have used compasses to navigate.

Compasses A compass is a tool that aligns itself with the magnetic field of earth with it’s north pole pointing towards Earth’s Magnetic South pole. People, however, might take the earth’s magnetic field for granted… what's the point?

Earths Magnetic Field The sun constantly bombards the earth with dangerous charged particles. Without the Earth’s Magnetic field, we would constantly be exposed to these particles… they would kill us… BUT the earth’s field spins these particles to our poles along it’s magnetic field lines… protecting us! Not only that… from this we also get…

Earth’s Magnetic Field Auroras! Also happens at the south pole (Aurora Australis) Also called the northern lights (Aurora Borealis)

Aurora This occurs when the charged particles make contact with the atmosphere. This happens on other planets as well! Aurora on Saturn

Back to Earth’s Magnetic Field: Why does the magnetic field on earth occur? The most common theory as to why Earth has a magnetic field is the fact that Earth is not a solid rock, but it has flowing currents of magma underneath its surface.

Earth’s Magnetic Field Convection currents in the Earth make the magnetic field. Also, as the magma sloshes back and forth, the magnetic field switch direction over long periods of time. This has happened more than 20 times in the past 5,000,000 years

Evidence? The Mid Atlantic Ridge: –Stripes in the rock along the ridge show how magnetic domains were oriented when the magma rose form the Earth’s core.

Practical Uses Compass Motors/ Generators Meters Maglev Trains Televisions

Magnetism and Electricity When charges flow through a wire they also generate a magnetic field around the wire. Changing the direction of the current changes the direction of the field.

Electromagnets An electromagnet can be made by coiling a wire and then passing a current through the wire. When coiled around a bar of iron this works even better since it aligns the domains in the iron.

Uses for electromagnets Maglev Trains, MRI, Construction, Particle accelerators, etc.

Charges and Magnetic Fields If a charge moves in relation to a magnetic field, the field will exert a force on the charge

Forces Continued A current-carrying wire is also deflected by a magnetic field. Direction of current determines direction of force.

Meters An ammeter works by passing a placing an electromagnet in a permanent magnet's field. These work in a similar way.

DC Motor Motors us these principles to work as well