Electromagnets and Electromagnetic Induction _ GCSE Physics

When a current flows through a wire it causes a magnetic field to be produced around the wire. For a single piece of wire, the magnetic field is made up of concentric circles around the centre. If you coil the wire up however, the magnetic field acts a lot like a standard bar magnet. The wire is usually wrapped around an iron cylinder, which increases the strength of the electromagnet. The useful thing about electromagnets is that they can be switched off. As soon as there is no current flowing through the wire, there is no magnetic field. That makes them handy for picking up heavy cars in a scrap yard and still being able to let them go. Just as a current can create a magnetic field. A magnet can create a current. This process is called electromagnetic induction. It works when a changing magnetic field produces a potential difference across a conductor, such as a wire. The way you do this is by moving a wire through a magnetic field back and forth repeatedly. As you move it one way it produces a potential difference, which is positive, and when you move it back, the p.d. is negative. This keeps alternating constantly, which is how you produce an alternating current. This is how generators work, except they get around the back and forth movement of the wire by having a magnet in the middle of a coil of wire that can spin. As the magnet spins, its polarity will swap every half turn, this will cause the p.d. across the wire to alternate every half turn and produce an alternating current to power our homes.