Magnetic Fields from Electric Currents.
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When an electric current is passed through a piece of wire a magnetic field
is produced. This is because magnetic fields are due to electric charges in
motion. Here we have our connection between electricity (
electric charges) and magnetic fields. The magnetic field lines that
form around a current carrying wire are however very different from
those produced around a bar magnetic. First of all, the magnetic field
lines form circles around the wire and secondly there are no North poles or
South Poles. Also when the current is turned off the magnetic
field vanishes.
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Simple ! Take the wire and wind it into a coil as shown to the right. When a
current is now passed through the wire a magnetic field similar to
that of a bar magnet is produced.
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In every day life magnetic fields produced by electrical currents are
comminly used. The most common use is called the electromagnet.
An electromagnet is just an electrical wire wound tightly around
an iron core. The strength of the magnet is determined by the
size of current in the wire and the iron core helps make the magnetic
field stronger. Electromagnets are used in electric drills and can infact be
strong enough to lift up a car !
Even if there are no electromagnets or bar magnets around us we are
continually surrounded by magnetic fields. This is because the earth
has a magnetic field.
