Magnetism

Magnetism

1. UNITS NEEDED TO KNOW

   • Ampere (A)
   • Volt (V)
   • Watt (W)

2. Opposite poles one magnets attract

   • Same poles repel
   • Magnetic substances can be attracted by a magnet

3. Magnetically hard materials retain their magnetism for a long time

   • Magnetically soft loses megnatic properties as soon as it leaves a magnetic field

4. Magnetic field line: represent shape and direction of megntic field

   • Some materials are not naturally magnetic
     • Magnetic fields align the electrons to form poles and make them magnetic (eg. iron)
       • Experiment: iron filings
         • Iron filings will line up around a magnet. They wil line up to the shape of the magnetic field. However to show the direction of it you must use compasses
       • Two bar magnets w/ north and south touching form the same magnetic field as one bar magnet (uniform)

5. An electric current through anything that conducts forms a magnetic field

   • Electromagnets: a wire is wrapped around a soft magnetic material
     • A current makes a magnetic field in the metal
       • If something with a charge moves across a magnetic field it will experience a force from the field
         • Motor
           • In a DC motor, there is a wire in a magnetic field. The force it experiences turns it around, this turns a 'split ring commutator' this basically is where charge goes from 'brushes' into the wires
           • Strength of magnet, number of coils, speed of rotation
         • Speaker
           • In a loud speaker, a coil is in a magnetic field. When a current is run through it the wire will experience a force that pushes it away from the field, this in turn pushes a cone which makes the sound. Whatever frequency the AC current is at, the coil will move at that frequency, making a note of a certain pitch.
     • Factors increasing generated electricity
   • Wire in magnetic field: if increase current there'll be more force on wire
     • If you increase strength of magnetic field: more force on wire
       • If you move a wire back and forth across a magnetic field a voltage will be induced
         • If you move a magnet back and forth through a coil of wire a voltage will be induced
           • If you increase the magnetic field strength, quicken the movement or increase the coils of wire you can increase the voltage induced
             • Rotate a magnet in a coil of wire and there will be a current induced

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