Magnetism Magnetism – the attraction or repulsion of magnetic materials.
Magnetism
15
W. Sautter 2007
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Describes magnetism and its relationship to electricity. **More good stuff available at: www.wsautter.com and http://www.youtube.com/results?search_query=wnsautter&aq=f
Transcript of Magnetism
W. Sautter 2007
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N
+
Fingers = magnetic flux lines North to South
Thumb = directionof + charge
Motion (current)
Palm = forceExerted onThe charge
Centripetal forceOn charge causedBy magnetic field
Charge moves in a circular path
N (magnet) S
By convention (everybody agrees) lines of magneticFlux leave the North pole and enter the South pole
Lines of flux are continuous and do not intersect each other.
LENZ’S LAW
When a magnet induces a current flow in a conductor, the induced current flows in a direction so as to create a magnetic field in the
conductor that opposes the original magnet field
N SMotion of magnet
Current in loop
ConductorWire loop
Direction of inducedfieldN
Using the Right Hand Rule
Direction of conventionalcurrent flow (fingers)
North end ofInduced Magnetic
Field (thumb)
N
Fingers = magnetic flux lines North to South
Thumb = directionof induced current
in the conductor
Palm = motionof conductor
in magneticfield
Conductor isMoved upward
In magnetic field
Induced EMF
0u
2 r
F = Force (newtons)B = Magnetic field strength (teslas)
Tesla = N / amps x metersL= conductor length (meters)
V = velocity of conductor thru field (meters/sec)Q = charge quantity (coulombs)
= angle between conductor and fieldmeasured from the perpendicular (degrees)
r = distance from the magnetic field source (meters)u0 = permittivity constant of material
(Free space = 8.85418782 × 10-12 m-3 kg-1 s4 A2 or 8.85418782 × 10-12 T x m /A
n = loops of conductor
PrimaryVoltage in
SecondaryVoltage out
n= number of turns ofwire in the coil
n voltage in coil
Voltage in coil current in the coil
current
Magnetic
field
Primarycoil
current
Secondarycoil
The magnetic field caused by thechanging current in the primarycoil radiates across the secondary
coil and induces a current in it.
A continually changing current in the primary is required fora transformer to work (D.C. will not work)
