Let us just quickly step back to our single conductor carrying an electrical current. 



Taking account of the "Right Hand Rule" you can see the direction of flow of the magnetic field. The fact that a magnetic field is created has useful applications but the magnitude of the field from one wire is not very powerful and would have limited practical use.


If we "bunched together" a large number of wires, the magnetic field generated by each would accumulate, and we get the same effect if we put the wire into a loop.

As we said before, the strength of the magnetic field produced changes with the current and the distance from the wire, the larger the current through the wire (or the closer you are to the wire) then the stronger the field is.


Notice that the field lines are very close together, and as we already said, when the field lines are close together the magnetic field is more powerful.


The strength of the magnetic field produced when the current passes through a wire can be enhanced by coiling the wire as shown in the diagram (and the animation if you're viewing this online). The reason for this is that the magnetic fields around each loop of the wire lineup to form an overall magnetic field shown.


This brings forward the concept of "the solenoid", which has a strong, uniform magnetic field throughout. This can be enhanced even further by placing a block of iron inside the coil because the iron becomes an "induced magnet" while the current is flowing. If we switch off the current the magnetism is lost, and this property has many applications, we have just invented the "electromagnet" :-)


So what's the difference between an electromagnet and a magnet? Well, in the case of an electromagnet the magnetic field can be switched on and off at will. You have seen, undoubtedly, electromagnets being used in scrap metal yards:


  • The large iron magnet (usually very heavy and round) is lowered into the scrap metal bunker. 
  • The electrical power is switched on causing a magnetic field to be created. 
  • The scrap metal is attracted by this magnetic field and sticks to the magnet. 
  • The strength of the magnetic field is such that the scrap metal can then be moved to another part of the yard or over the top of a lorry (or indeed it may be coming out of a lorry). 
  • Electrical power is shut off, the magnetism vanishes and the scrap metal falls away from the magnet to its new location.


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