Physics 123

20. Magnetism 20.1 Magnets and magnetic fields 20.2 Electric currents produce magnetism 20.3 Force on current in magnetic field 20.4 Force on moving charge in magnetic field 20.5 Magnetic field due to a straight wire 20.6 Force between two parallel wires

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

Electric Currents Produce Magnetism Right-Hand Rule: Thumb points to current ( I) and curled fingers indicate B I B B

Electric Currents Produce Magnetism Old wine … New bottle! I X

Electric Currents Produce Magnetism Right Hand Rule: Thumb points to B and curled fingers indicate I I I B

Electric Currents Produce Magnetism I I Old wine … New bottle!

Force on current in magnetic field 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

Force on current in magnetic field I Force = BIL sin  B 

Force on current in magnetic field 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

Force on moving charge X X X X X X e

Force on moving charge X X X X X X e

Force on moving charge F = B e v X X X X X e

Electric Currents Produce Magnetism I B B B =  o I / 2  r

Electric Currents Produce Magnetism I I B B =  o I / 2 r

Force between two currents F =  o I 1 I 2 L / 2  r I1I1 I2I2

That’s all folks!