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Magnetism and Electric Currents Magnetism and Electric Currents • The connection between electricity and magnetism was discovered accidentally by the Danish scientist Hans Christian Oersted (1777– 1851) in 1820. • Oersted was giving a science lecture when he closed a switch and allowed a current to flow through a wire. He noticed that a nearby compass needle rotated rapidly when the switch was closed. • With that simple observation, Oersted discovered that electric currents can create magnetic fields. Magnetic Field Produced by an Electric Current • The magnetic field "circulates" around a wire carrying current • The field lines are concentric circles around the wire Magnetic Field Produced by an Electric Current • Placing several compasses around the wire also shows that the field lines are circles, but it will also show the field’s direction. Right Hand Rule for Magnetic Fields • To find the direction of the magnetic field produced by a current, point the thumb of the right hand in the direction of the current • The fingers then curl in the direction of the magnetic field Strength of the Magnetic Field Produced by a Current • The magnetic field produced by a current in a wire is – Directly proportional to the current – Inversely proportional to the distance from the wire. Magnetic Field Produced by a Loop of Wire Carrying Current • Using the right hand rule, the field lines produced by a current moving through a loop of wire all point through the middle of that loop Magnetic Field Produced by a Loop of Wire Carrying Current • This makes the loop behave like it was a bar magnet • One side of the loop behaves like a north magnetic pole • The other side like a south magnetic pole Magnetic Field Produced by a Loop of Wire Carrying Current • When two loops with the same current are placed next to one another, the magnetic field is strengthened Electromagnets • A solenoid is a long wire wound into many closely spaced loops forming a coil • When current passes through the wound up wire, it produces a strong magnetic field inside of the coil • This is referred to as an electromagnet because the magnetic field only exists when current flows through the wire Electromagnets and a Galvanometer • A galvanometer consists of a coil of wire surrounded by magnets • As a current passes through the galvanometer's coil, a magnetic field is created • This field interacts with the field from the magnets and causes the coil to rotate, which moves the needle • Galvanometers can be used to measure current Electromagnets and Electric Motors • Same basic arrangement as a galvanometer – a coil of wire surrounded by magnets • When current passes through the wire, a magnetic field is created which interacts with the magnets, causing the coil to rotate • If the coil is attached to an axle, it can turn a motor and power anything that spins