Physics 223

29. Magnetic Fields 29.1 Magnetic Fields (B) and Forces (F) 29.2 Motion of a Charged Particle in B 29.3 Applications: Charged Particle in B 29.4 Magnetic Force on Current in a Wire 29.5 Torque on a Current Loop in B

Magnets and magnetic fields 1. Unlike poles attract 2. A magnet will also attract magnetic materials that are not magnets (induced magnetism) 3. Monopoles do not exist? 4. Use a compass to trace the magnetic field (closed loops!) NS

Force on moving charge X X X X X X e

Force on moving charge X X X X X X e Right Hand Rule: Fingers indicate I, curled fingers B and thumb points to direction of force

29.2 Motion of Charged Particle in B F = B e v X X X X X e

Bev’s Legal Name F = q v x B

29.3 Applications: Mass Spectrometer Bev = m v 2 /r r = m v /e B X X X X X e

29.4 Force on Current-Carrying Wire in B I B X Force on wire INTO the page Right Hand Rule: Fingers indicate I, curled fingers B and thumb points to direction of force

Force on current in magnetic field I B Force = BIL

BIL’s Legal Name I F = I L x B Force = BIL sin  B 

29.5 Torque on Current Loop in B I = 1.5 A, B = 0.04 T, coil is 3 cm x 2 cm. Calculate the torque on the coil.

Torque on coil in magnetic field F = BIL F= 1.8 x N  = F x W = 3.6 x m.N

DC Motor  = BINA

BINA’s Legal Name  =  x B

That’s all folks!