Phys 4, Section 2 Feb 13, 2002
Magnetism (Permanent Magnets)
Magnetism: first noticed as effect of iron ores by Greeks in Magnesia.
Magnetic field B is caused by moving charge (current); this field is experienced by other moving charges.
F = qυ × B (Units of B are Tesla: 1 T = 1 N/A · m; also gauss: 1 G = 10-4 T)
Lorentz Force: F = q(E + υ × B)
Magnetic Field Lines and Magnetic Flux
Field lines come out of N poles and go into S poles, except within the magnet itself where the lines go from S to N. Magnetic field lines have no origination or destination points, but always form closed loops.
Magnetic flux is defined:
Gauss' Law for Magnetism:
Charged Particles in B
Magnetic force F is at right angles to motion υ of charged particle q, so does no work, but can only change direction of motion, it acts as a centripetal force driving the particle in circular motion of radius R:
so get ω = qB/m (cyclotron frequency).
Crossed B and E fields (balance of E-force and B-force):
velocity selector: υ = E/B
Last modified on February 27, 2002