Magnetism

1. Magnetism Or Pimpin’ for Electricity

2. Where do we observe magnetism? • Permanent magnets, around a current carrying wire and inside a looped wire • All of these involve accelerating electric charges. • Magnetism in general • Force between poles. Like poles repel, opposites attract • Produces fields that follow inverse square law with distance • Field direction North to South by convention • No magnetic monopoles • Magnetic force aligns magnetic particles • Magnetic fields made of loops

3. Permanent Magnets • Fe, Co, Ni, Nd have unpaired electrons in outer D orbitals with the same spin and can become magnets • Domain theory and Magnetic vs. non-magnetic iron • Dropping or heating magnet reduces strength • Cutting magnet in half results in two magnets both with a N and S pole.

4. Magnetic field around a current carrying wire • Field in shape of concentric loops • Field weakens as inverse square of distance from wire, direct relationship w/ current • RHR #2: Thumb in direction of current, fingers curl in direction of magnetic field

5. Looped Wire • More magnetization because have both linear and centripetal acceleration of charge • Magnetization is greatest inside of wire because of concentration of field lines in same direction • RHR #1 fingers curl in direction of conventional current, thumb points to north pole • RHR #1 also applies to single charges that spin or circle.

6. The Earth’s Magnetic Field • Shape of field is like a bar magnet • Believed to be caused by circulating charged ions in mantle and outer core • Field changes direction and strength over time • Field deflects charged particles from sun making life possible