Field Around Magnet Use a compass to map

Field Around Magnet • • Use a compass to map the direction of the magnetic field surrounding a magnet. White board your results. In particular: • • how does the strength of the field vary with distance from the wire? how does the field direction relate to the poles of the magnet? General Physics 2 Magnetism 1

Activity: Map Field of Magnets • Use iron filings to map the field of a • • • bar magnet horseshoe magnet White board results • • draw field lines. how might magnets generate magnetic fields? General Physics 2 Magnetism 2

Magnetic Field Lines • • direction of magnetic field, B, is parallel to field line number of lines per area is proportional to strength of field • field lines point from N to S • field lines form closed loops General Physics 2 Magnetism 3

Magnetism No magnetic monopoles! General Physics 2 Magnetism 4

Magnets are similar to Electric Dipoles General Physics 2 Magnetism 5

Ferromagnetism • Ferromagnetic material • • Preferentially downwards You can make a magnet from iron by placing it in a strong B field • • iron or other materials that can be made into magnets Random individual domains become aligned with external B field Loss of magnetism from: • • dropping heating • Curie temperature • 1043 K for iron General Physics 2 Magnetism 6

Cross Product – Right Hand Rule General Physics 2 Magnetism 7

Specifying 3 Dimensions • out of page • tip of arrow General Physics 2 • into page • tail of arrow Magnetism 8

Force on a moving charge • Right Hand Rule (#2) • • qv = fingers B = bend fingers F = thumb Find the direction of the force on a negative charge for each diagram shown. General Physics 2 Magnetism 9

General Physics 2 Magnetism 10

Think-Pair-Share • Derive an expression for the radius of an e’s orbit in a uniform B field. Express your answer in terms of me, v, qe, and B. Turn in your solution! General Physics 2 Magnetism 11

Earth’s Magnetic Field • magnetic declination • • General Physics 2 Magnetism angular difference between geographic north and magnetic north varies with latitude 12

Practice Problems • Magnetism: Worksheets 1 & 2 • Finish before next class General Physics 2 Magnetism 13