Elec 3

• If you pass a current through any wire, a weak magnetic field is produced
• This link between electricity and magnetism has been thoroughly investigated, enabling us to make very powerful, controllable electromagnets
• Electromagnet


  A magnet that uses electricity to produce a magnetic field
• Oersted's discovery of electromagnetism

  1. Passed a current through a single wire

  2. Placed a compass near the wire

  3. Noticed the needle moved, proving a magnetic field was present

  4. When the current was switched off, the needle returned to its normal position
• Oersted had taken the first steps towards understanding electromagnetism
• Any wire with a current passing through it

  • Produces a magnetic field
  • When the current is switched off, the magnetic field disappears
• Electromagnet


  A temporary magnet as it only produces a magnetic field when the current flows
• Electromagnet vs permanent magnet

  Electromagnet only produces a magnetic field when current flows, permanent magnet produces a constant magnetic field
• Proving an electromagnet is magnetic


  Two different ways
• Making an electromagnet stronger

  1. Increase the current passing through the wire

  2. Make the wire into a coil

  3. Increase the number of coils in the wire

  4. Put an iron core in the centre of the coil
• Solenoid


  A coil of wire wound around a core
• Demonstrating an electromagnet


  1. Battery and coil of wire surrounding an iron nail

  2. Wire is covered by electrical insulation

  3. When current is passed through wire, it causes the iron nail to become magnetic
• Modifying an electromagnet


  To attract and lift a car
• Dropping the car


  How to do it
• The magnetic field shape around a wire with current is circular
• The shape of the magnetic field around a long coil of current-carrying wire is similar to that of a bar magnet
• Reversing the direction of the current reverses the magnetic field
• Increasing the number of coils increases the magnetic field around the loops, resulting in a stronger field
• Using a magnetic material, like iron, as a core strengthens the field
• Advantages of an electromagnet over a permanent magnet


  For devices that require a magnet
• If the current in Figure 2.2.3d is increased


  The magnetic field lines would increase
• The coils of an electromagnet are placed in line and not in a random way
• The core is made of iron