Magnetism and Magnetic Fields

Magnetism and Magnetic Fields

1. Magnetic field is a region where a magnetic material experiences a force.

   • Magnetic field lines go from North to South.
     • Closer the magnetic field lines are, the stronger the magnetic field at that point.
       • Strength of magnetic field is called magnetic flux density. Measured in (Teslas).

2. Like poles repel, unlike poles attract

   • When a magnet is brought near a magnetic material then that material acts as a magnet.
     • This magnetism has been induced by the original magnet. The closer the magnet and the magnetic material get the stronger the induced magnetism.
       • Induced magnets will usually lose their magnetism once the magnet has been moved away, compared to a permanent magnet.

3. An electrical current in a material produces a magnetic field around it.

   • Larger the electric current, the stronger the magnetic field
     • Magnetic field around a straight, current-carrying wire is made up of concentric circles with the wire in the centre.
       • The further away from the wire, the weaker the magnetic field. Non-linear relationship.
         • Lots of coils joined together to make a solenoid, the magnetic effect is increased.
           • Outside the coil, field is just like the one around a bar magnet.
           • Ends of a solenoid act like the north and south pole of a bar magnet. This type of a magnet is called an electromagnet.
             • Magnetic effect at the poles of a solenoid will increase if the current is increased, the number of turns has increased, but the lengths stays the same. An iron core is added inside the solenoid.
               • When a current carrying wire i put between magnetic field poles, the two magnetic fields affect one another.
                 • Wire has to be at 90 degrees to the to the magnetic field. If the wire runs along the magnetic field, it wont experience any force at all.
                   • Force acts in the same direction relative to the magnetic field of the magnets and the direction of the current in the wire. Changing the direction of either the magnetic field or the current will change the direction of the force.
                     • In a simple direct current motor, a current - carrying coil sits between two opposite poles of a magnet.
                       • Because the current is flowing in different directions on each side of the coil, and each side of the coil is perpendicular to the magnetic field, each side will experience forces in opposite directons.
                         • Because the coil of wire is on a spindle, and the forces act in opposite directions on each side, it rotates.
                           • Split ring commutator is a clever way of swapping the contacts every half turn to keep the motor rotating in the same direction.
                 • Force gets stronger if either current or magnetic field is made stronger.