Magnetic Field: General Phenomena +q, -q Electric Field (E)Magnetic Field North and south poles Like/dislike charges repel/attractLike/dislike poles repel/attract There is no magnetic monopole: north and south poles ALWAYS come in pairs Magnetic field: Outside a magnet: N to S Inside a magnet: S to N Magnetic field lines always close on themselves: no source or drain.

General Phenomena: Continue 1.Magnets only attract certain materials Magnetic materials: Fe, Co, Ni & some rare earths Sm. Nd. Some magnetic materials can generate magnetic field: Permanent magnet 2. Action at distance (through field): demo only magnetic materials can shield magnetic field

Charges in a magnetic field Concept Check In which situation does the magnetic field points to the left? -++× V FBFB · FBFB FBFB V V (A)(B)(C) Answer: (A) Right hand Rule

Magnetic Force on a MOVING charges: Continue 1.F=0 if V=0 V||B 2. If F  B (or V  B ), what type of motion does a charge have? Circular motion: accelerator, mass spectrometer B field can be used to change the direction of a moving charge magnetic force cannot do work on a charge. Magnetic field cannot change the speed of a charge, only E field can Net EM force on a charge:

Circular Motion: General × × × -q V F r

Circular Motion: Plane  B × × × -q V F r Circular path: V || =0 Helical path: V ||  0