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Magnets and Magnetic Fields
Bar magnets have two poles: north and south
Opposite poles attract, like poles repel (similar to electric charge): BUT: Unlike electric charge, there are NO isolated single magnetic poles (monopoles).
Magnetic fields surround magnets and are described by magnetic field lines so that: (i) the direction of the field is tangent to the line at a point; (ii) magnitude of the field is proportional to the number of lines per unit area. Because of this, magnetic fields are
vectors, denoted by B
Magnetic poles versus geographic poles
Magnetic declination: angle between magnetic north pole and true (geographic) north pole
Magnetic angle of dip: angle between tangent line to earth’s surface at a point and magnetic field line.
Electric Currents Produce Magnetic Fields
In 1820, Hans Christian Oersted discovered that a compass near an electric wire causes the needle to deflect. Thus, he found a connection between electricity and magnetism: an electric current produces a magnetic field.
Right-Hand-Rule-1 (RHR-1): Thumb on right hand points in direction of positive current; then fingers encircle wire in the direction of the magnetic field.
