Magnetism

Permanent and Induced Magnetism

All magnets produce a magnetic field, in which other magnetic materials can feel a force (non contact) This magnetic field is strongest at the poles of a magnet, which means the forces are also the strongest here When two poles are placed near each other, they will either attract or repel. Like poles will repel, whereas opposite poles will attract. There are two types of magnet, permanent and induced. Permanent magnets produce their own magnetic field whereas induced magnets are magnetic materials that turn into a magnet when theyre put into a magnetic field. Permanent and induced magnets always attract each other, however removing the magnetic field will result in the induced magnet to lose their magnetism.  

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Compasses

Inside a compass is a tiny bar magnet The north pole of this magnet is attracted to any south pole near it, so the compass points in the direction of the magnetic field it is in  When theyre not near a magnet, compasses always point north because Earth generates its own magnetic field, which shows the inside core of the earth must be magnetic

Electromagnetism

When a current flows through a wire, a magnetic field is created around a wire. Changing the direction of the current changes the direction of the magnetic field. The strength of the magnetic field produced changes with the current and distance from the wire. The larger the current through the wire, or the closer to the wire you are, the stronger the field is.  A solenoid is a coil of wire, and can increase the strength of a magnetic field.  This happens because the field lines around each loop of wire line up with each other. This means lots of field lines point in the same direction that are very close to each other.  The magnetic field inside a solenoid is strong and uniform, and the magnetic field outside the coil is the same as a bar magnet. 

To increase the strength of a magnetic field you can PIT Put an iron core in the middle  Increase the current  Turn more coils Electromagnets have a lot of uses, such as being used in cranes and circuits.   

The Motor Effect

When a current carrying wire is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in. This causes the magnet and the conductor to exert a force on each other, resulting in the wire to move. This is called the motor effect.  To be at full force, the wire has to be 90 degrees to the magnetic field. If it is parallel, there will be no force, and any angles in between will only experience some force.  The magnitude (strength) of the force increases with the strength of the magnetic field. The force also increases with the amount of current.  The size of a force can be calculated by using this formula: Force=Magnetic Flux Density X Current X Length The MFD is the amount of field lies in the region, and shows the strength of the field. 

The Left Hand Rule To calculate Left Hand Rule, remember this: thuMb - Motion/Force First Finger - Field seCond finger - Current

Electric Motors

The diagram on the right shows a basic dc motor Forces act on both arms, one up and one down, causing the motor to rotate By reversing the current, and swapping the magnetic poles, you can reverse the direction of rotation. 

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Rubrica: : Basic DC Motor