## Magnetism

Thr north pole is the end of the magnet pointing towards the north-pole of the earth. The north pole of one magnet attracts the southpoles of another magnet. If one tries to break a magnet into two the effort is futile because the result is two new magnets each having its own south- and north-pole.
The earth itself acts as a huge magnet having its magnetis southpole close to the geographic north-pole.
H. C. Örsted discovered in 1820 that currents in wires produces magnetic fields around them. A simple rule for rememebering the direction of the magnetic field is the right-hand rule. It states that if one grasps the wire with the right hand in such a way that the thumb points in the direction of of the current the fingers then circle the wire in the same sense as the magnetic field.
There is a far reaching similarity between the magnetiv magnetic around a coil and a bar-magnet.

A wire carrying a current through a magnetic field experience a force. This force can be calculated with the following formula:
F = L i x B.
Here B is the Magnetic flux density.

Since I = Q/t F = L Q/t B = QvxB
The resulting force acting on a charged particle moving in an Electric and magnetic field is thus given by the Lorentz-relation: F = qE + QvxB.

The field -strength a distance r outside a wire carrying the current I is given by

B = μI/(2πr) ## Om mattelararen

Licentiate of Philosophy in atomic Physics Master of Science in Physics
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