Magnetism and Electromagnetism #1

Magnetism and Electromagnetism #1

1. Magnets and Magnetic Fields

   • All magnets have 2 poles - north and south
   • A magnetic field is a region where magnetic materials experience a force
   • Magnetic field lines are used to show the size and direction of magnetic field
     • They always point from north TO south
   • Placing the north and south poles of 2 permanent bar magnets near each other creates a uniform field between the 2 magnets
   • Magnetic field lines using a compass
     • Compasses and iron filings align themselves with magnetic fields
     • Using multiple compasses to see the magnetic field lines coming out of a bar magnet or between 2 bar magnets
   • Magnets affect magnetic materials and other magnets
   • 'Like' poles repel each other and opposite poles attract
   • Both poles attract magnetic materials (that aren't magnets)
   • When magnetic materials are brought into a magnet's field, 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 will be

2. Electromagnetism

   • A current carrying wire creates a magnetic field
     • An electric current in a conductor produces a magnetic field around it
       • The larger the electric current, the stronger the magnetic field
   • Straight wire
     • There is a magnetic field around a straight, current-carrying wire
       • The field is made up of concentric circles with a wire in the centre
   • Flat circular coil
     • The magnetic field in the centre of a flat circular coil of wire is similar to that of a bar magnet
   • Solenoid
     • 1. The magnetic field inside a current-carrying solenoid is strong and uniform
       • 2. Outside the coil, the field is just like the one around a bar magnet
         • 3. This means that the ends of a solenoid act like the north and south pole of a bar magnet.
           • This is called an ELECTROMAGNET
   • Magnetic materials are soft or hard
     • A SOFT magnetic material loses its induced magnetism quickly
       • e.g. iron
         • Iron is used in transformers because of this
     • A HARD magnetic material keeps its induced magnetism permanently
       • e.g. steel
     • Increase by strength of the magnetic field around a solenoid by adding a magnetically soft iron core through the middle of the coil

3. The Motor Effect

   • Happens when you put a current-carrying wire in a magnetic field
   • When a current-carrying wire is put between magnetic poles, the 2 magnetic fields affect one another
     • The result is a force on the wire, causing it to move - this is the motor effect
     • This is because charged particles moving through a magnetic field will experience a force
   • 1. To experience full force, the wire has to be at 90° to the magnetic field
     • 2. If the wire runs along the magnetic field it won't experience any force at all
       • 3. The force always acts in the same direction relative to the magnetic field of the magnets and the direction of the current in the wire
         • 4. A good way of showing the direction of the force is to apply a current to a set of rails inside the horseshoe magnet
           • 5. A bar is placed on the rails, which completes the circuit. This generates a force that rolls the bar along the rails
             • 6. The magnitude of the force increases with the strength of the magnetic field
               • 7. The force also increases with the amount of current passing through the conductor
                 • 8. Reversing the current or the magnetic field also reverses the direction of the force

4. Fleming's Left-Hand Rule

   • Field
     • First finger
   • Current
     • Second finger
   • Direction of force - motion
     • Thumb