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Physical Science Notes 416-436
Magnetism
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Magnetism: Quite the attractive subject

Magnetism

 

Important terms:

 

                -Natural magnets: lodestones = chunks of iron ore

                -Magnets: steel = made magnetic by stroking

                -Ferromagnetic: FeNiCo (Iron, Nickel, Cobalt) = attracted to a magnet

                -Non-magnetic: everything except: FeNiCo = e.g.: Cu, Al, wood, glass etc

-Domains: clusters/groups of molecules in ferromagnetic substances that align themselves when a magnet is present

-Remanence / retentivity: the ability to become or to remain magnetized

                -Magnetically soft: becomes magnet easily but does not stay magnetic once magnet is removed

-Magnetically hard: hard to become magnetic but stays magnetic for awhile once magnet is removed

-Magnetic field: area around a magnet where the effects if the magnet can be felt

-Electromagnet: Gets magnetized when electricity is passed through it (e.g.: solenoid)

-Solenoid: type of electromagnet, a coil of wire that becomes magnetic when power is passed through

-Poles: magnetic North pole(N) and South pole(S)

 

Magnets:

 

Magnets have two poles; a North and a South pole. They do NOT have a positive (+ve) and a negative (-ve). If they do not have a north or south pole they are not magnets.

 

Magnetic Domains:

 

Only ferromagnetic substances, FeNiCo, have domains that align themselves in the presence of a magnet.

 

-If you are given a piece of Iron, Nickel or Cobalt and were able to see the domains inside of the piece you would see a whole bunch of clusters of molecules in no order. Then if you put the north or south pole of a magnet near that piece of metal you would notice that all the little domain inside would align themselves. This happens because all those little clusters of molecules are like little bar magnets. Therefore each cluster has a north and a south pole. So when a magnet is present the opposite charge would be attracted to the magnet.

magneticdomains.jpg

Magnetic fields:

 

All different types of magnets have magnetic fields. To discover what the magnetic field of a certain magnet looks like there is simple way to do it. There are also a few specific properties that make magnetic field lines.

 

Specific properties:

                        -They never cross

                        -Move from the north to the south

                        -Indicate a stronger magnetic field (at the poles) when they are close together

                                -They dont actually exist

 

If you want to find out the magnetic field of a certain type of magnet all you have to do is sprinkle iron fillings around the magnet. Bang the table that you have the fillings on so that they spread out more. Observe the pattern that the fillings create, the lines are the magnets magnetic field. Note: bar magnets and a solenoid have the same shape of magnetic field.

magnets.jpg

Compass:

 

The needle of a compass is a magnet. Therefore a compasses needle has a North pole and a South pole. The painted end of the compass needle is the north pole of the compass. But there is a problem with that, this is the problem and the solution:

 

The compass needle always points north. But the north pole of the compass is pointing north, therefore what does that tell you about the earths North pole? Well the earths North pole is actually a South pole! In Physical Science 416-436 you dont have to know why, so one less thing to worry about it. The reason you might be told this is to help explain how a compass works when placed around a magnet. This topic is related to the magnetic field.

 

If you place a compass around a magnet you can see in which direction the magnetic lines are coming from, therefore telling you which part is North pole and the South pole. This is shown because magnetic field lines go from the North pole to the South. So if a compass placed at end A points to end B, end A is North and B is South. The picture below will help explain:

compassbarmagnet.jpg

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