Note for next year: I don’t get Ampere’s law

Note for next year: I don’t get Ampere’s law Clean up this unit- see AP objectives

Magnetism This train does not roll on wheels. All its weight floats on magnets.

Misc pictures to ebed later

Magnetism was discovered over 2,000 years ago. The first magnets were natural rocks called lodestones. Magnetism was named for the region of Greece (Magnesia) where these rocks were found.

No matter the shape, Magnets have two sides or “poles” S N North pole N N N South pole S S S N S

N S N N S S N N S S N S If you break a magnet N S

You could keep breaking the magnet until you were down to a single atom N S AND IT too would act as a magnet with a north and south pole.

As before LIKES POLES REPEL OPPOSITE ATTRACT S N N N S S REPEL REPEL ATTRACT N S N S N S

The earth is also a magnet. It has North and South Magnetic Poles (a little off from geographic poles)

Compasses use a magnetized needle which points to the magnetic poles of the planet (a little off from geographic poles) N N W W E E S S

Notice a compass would not work too well here.

N W E S N The North Pole of a magnet is the one that is attracted to the North Pole of the earth S Which really means that the north magnetic pole is by definition the south pole of a magnet since they attract. (But this is just trivia).

N W E S Until 1820, people thought electricity and magnetism were unrelated. Until Hans Christian Oersted made a discovery during a class.

N W E S When the switch was closed and current flowed, the compass needle moved!!!! animation

ELECTRICITY AND MAGNETISM are VERY RELATED MAGNETIC Fields are created by moving charged particles

Electricity & Magnetism Similar because: Likes repel Opposites attract

N S Electricity & Magnetism Different because: Positive and negative charges exist independent of each other P+ e- YOU cannot have a N pole without a S pole t S S N N ETC +

Electricity & Magnetism Similar because: They both (like gravity) exert a force without contact. That really bugs me.

Electricity & Magnetism Similar because: THEY BOTH CREATE FORCE FIELDS

Field lines arrows run from N to S poles. Is a north pole like a + or - charge?

Where is the field the strongest?

Magnetic Field Strength has units of : TESLA (T) Magnetic Field Surface of a Neutron Star 100,000,000 Surface of a strong magnet 10 Near earth’s magnetic poles .00005 gauss (G) is also used sometimes 1 G = 10-4 T The variable for magnetic field is B.

Magnetic field lines are mapped out by using another magnet like a compass Phet magnet simulation

A magnet will align itself with field lines

N A magnet will align itself with field lines, when the torques balance out around the needle pivot. Think back to torque, how does the large red force balance the small blue force. S

N Why do magnetic field lines have to be mapped out with both a N and S pole? Why can’t we just put a N pole in the field and map out the net force on it like we did with electric field with a + test charge? S

Iron filings will trace out field lines because they become temporarily magnetized.

Magnetic Fields are really 3D

Last sub-level of Fe- ferromagnetic Zn- Non magnetic 3d ___ ___ ___ ___ ___ 3d ___ ___ ___ ___ ___ Magnetism originatesin the motion of the electrons in iron. Spinning electrons act like tiny magnets. Almost 100 % cancellation of this effect occurs in mostmaterials. Iron, nickel, cobalt areexceptions.

Little regions of a ferro-magnetic material, have the unpaired electrons align image of domains (using a special method to show magnetic fields, domains are not visible even with a microscope)

domains can be forced to align by a magnetic field. they will temporarily stay aligned heating or banging tends to unalign them again

This is why certain materials become magnetic when touching a magnet. Because the domains align in the field (the coins must be made with Fe, Ni, or Co) N S N S N S S N N S

In order for the to be an electric force between 2 objects. Both objects must have charges or induced charges. Attract Repel - + + + - + - - + + - + - - - + + - - + - + + so this is really an interaction between 2 electric fields NADA neutron electron

A permanent and iron nail (an induced magnet) N S A permanent and copper wire two permanent magnets S S N N attract S repel NADA S N N

Magnet activity: things to see or try put a pencil through all 3 magnets, can you make them levitate? how does a magnet affect a compass does a compass affect another compass Place the magnet flat under the magnetic viewer Place the magnet on an edge under the magnetic viewer (How does it differ, remember you are viewing field lines)

Next Topic -- Electric current produces a magnetic field

If a magnet and electron are both stationary, there is no force between them. because there is only: 1 magnetic field & 1 electric field e-

e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- e- If the electron(s) are moving then… moving charged particles (like electricity) produce a magnetic field. FORCE

Magnetic Field lines around a wire carrying current.

Magnetic Field Lines follow the right hand rule current

Which way is current flowing?

Which way would the magnetic field point inside a loop if the current is traveling in a loop? I

Common convention is to use x’s (into the page) and circles (out of the page) to show magnetic fields etc…. Shouldn’t have to memorize this I I Out of the “page” Into the “page”

When the wire forms a loop the field concentrates at the center. We’ll come back to this.

vacuum permeability = 4p x 10-7 T m/A current (A) mo I B = 2 p r distance from wire magnetic field strength around a straight wire

15 A of current flows through a wire to the left, what is the strength and direction of the magnetic field 15 cm above the wire. I

15 A of current flows through both wires below. If they are seperated by a distance of 30 cm. What will the magnetic field strength be midway between the? I I

The field is strongest in the middle of the loop the more the loops the stronger the field

Note for next year: I don’t get Ampere’s law