Magnetic field

The giant terrestrial magnet

The inset shows the lines of force caused by the magnetic properties of the Earth.

Note how the lines leave the south pole (the magnetic north) and enter the north pole (the magnetic south).

Observe how compasses point north as a consequence.

It is important to note that the magnetic poles do not coincide with the geographic poles. From every point on the Earth, there is

a difference of a few degrees between the direction in which a compass points and the direction of the geographical north pole. The difference is called magnetic declination. The magnetic declination changes slowly as time goes by. This means that the magnetic poles move. In fact, the polarity of the Earth, changes in irregular geological time periods.

	Natural magnets
	Lines of force
	Magnets and currents
	Conclusions

	on a charged particle
	on a straight cable
	on a loop
	Conclusions

	by a charged particle
	by a rectilinear current
	by a coil
	An explanation of natural magnetism
	Conclusions

	Magnetic flux
	The laws of Faraday and Lenz
	Self-induction
	Conclusions

	The generation of alternating currents
	A circuit of alternating current
	Conclusions