Electromagnetic Induction - Concepts
1. Magnetic Flux
If B is at 90° to the area, A, then the total magnetic flux,
"passing through"
A is the number of lines of force (or magnetic field) passing through area A, or
= AB
The units of flux are Tm² and 1 Tm² = 1 Weber
2. Generated Voltage from Changing B (mag field)
Induced Voltage = (number of turns)(change in flux)/elapsed time)
v
N
t
This is Faraday’s Law (named after Michael Faraday).
Electromagnetic Induction
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FDHS Physics
The induced emf (generated voltage) can be calculated from Faraday's Law.
According to Lenz's Law the induced current in the coil produces a magnetic
field to oppose the change in magnetic field that produced it. Observing the
direction of the change in the magnetic field of the bar magnet, you know that
the induced current will produce a magnetic field in the opposite direction
called the induced field. If you put the fingers of your right hand inside the coil
in the direction of that induced field, the thumb points in the direction the
current must flow to produce the field.
3. Transformers
-
a device that increases or decreases a voltage of alternating current.
-
An AC voltage in a primary winding (Vp) induces an AC voltage in the
secondary winding (Vs), according to the ratio of the # of turns of
wire (Np/Ns), per
o Vp/Vs = Np/Ns
o Power is constant, or Pp = Ps
o Step-up => Vs > Vp
o Step-down => Vp > Vs
Electromagnetic Induction
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FDHS Physics