How was the connection between electric currents and magnetic force discovered?
(Students tell about it, or else, the teacher.) What are magnetic field lines? Base your definition on the magnetic needle described above. • They are imaginary lines giving at each point the direction in which our 3-D needle would point, if placed there. What are magnetic field lines used for? • They were originally used to graphically describe magnetic fields. In the rarefied plasmas of space, however, they also guide the flow of particles and currents. This is why arching solar formations above magnetic sunspots sometimes resemble the field lines of bar magnets. (The guiding property of field lines also makes possible the trapping around Earth of ions and electrons in the Earth’s radiation belts. The motion of these particles stops and reverses before they hit the Earth, because they are also reflected from regions of stronger magnetic field, found closer to Earth.) What is Andre-Marie Ampere remembered for? • He explained the observations which baffled Oersted, and in doing so gave
