1 Lecture series for Conceptual Physics, 8 th Ed.

2 Introduction p years ago- Magnesia, a Greek province…lodestones. 12 th century- Chinese made lodestone compasses. 16 th century- William Gilbert suggested that the Earth was a magnet John Michell found that magnets obeyed inverse square law. Later confirmed by Charles Coulomb Hans Oersted discovered that electric current affected a compass Andre-Marie Ampere proposed that electric currents are the source of magnetism.

3 Magnetic Forces p419 Coulomb’s Law only works when the charges are standing still. (electrostatic) Moving charges create magnetic fields which also exert forces. Magnetic Poles p419 Notice magnetic field lines. Like poles repel; opposite poles attract. A magnet is always a dipole. A single iron atom spins to create a north and south pole.

4 Magnetic Fields p420 Iron fillings line up in the magnetic field around a bar magnet. Starting at the North pole, the magnetic field lines loop around to the South pole and then return through the magnet back to the North pole. Cobalt, nickel and iron are the 3 elements whose electrons orbit and spin in a particular way to produce a magnetic field. Magnetic Domains p421 Normally tiny areas of magnetism in iron cancel. Under certain circumstances the domains line up.

5 Fig 23.7 p422 By the way, domains in a non-magnetized piece of iron can be induced to align in the field of a magnet.

6 Electric Currents and Magnetic Fields p423 Current, moving charges, create a magnetic field around the wire. Note the geometry of the magnetic field created by the loop. Electromagnets p424 A bunch of loops. Right Hand Rule #1 If you line up your right thumb in the direction of the current, then your fingers curl in the direction of the magnetic field.

7 Electric Meters p426 A sensitive current-indicating instrument is called a galvanometer. Luigi Galvani, 18 th cent., was dissecting a frog (my kind of guy) when he noticed its leg muscle twitch when a small current was applied. This lead to the invention of the battery. I Magnetic field lines North end of compass lines up in magnetic field.

8 Electric Motors p427 Commutator,stationary in this picture, allows the yellow loop to rotate around changing polarity each ½ turn. The fluctuating current in the loop produces a fluctuating magnetic field which interacts with the permanent magnet to make it turn.

9 Earth’s Magnetic Field p428 A theory about how the Earth creates a magnetic field involves convection currents in the core.

10 More on Earth’s Magnetic Field p429 High energy, charged particles called cosmic rays get trapped in Earh’s magnetic field. The areas where these particles are stuck are called Van Allen radiation belts. Cosmic rays are channeled to the North and South Poles where they hit the upper atmosphere. Biomagnetism p431 The end