Applications of Electromagnetism. Electromagnetic Waves.
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Transcript of Applications of Electromagnetism. Electromagnetic Waves.
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Applications of Electromagnetism
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Electromagnetic Waves
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A changing magnetic field generates an electric field.
B E
A changing electric field generates a magnetic field.
E B
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changing E
ELECTROMAGNETIC WAVE
speed = c (speed of light; 3.00 x 108 m/s)
changing B
changing Echanging B
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EM Wave
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E ┴ B ┴ v
v
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EM waves produced by accelerated electric charges.
To produce an EM wave:
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Electromagnetic Spectrum
v = λ f
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Transformers
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A changing magnetic field in the primary coil induces a current in the secondary coil.
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Use an alternating current to produce a constantlychanging magnetic field.
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EMF in a coil depends on the number of turns of wire in that coil.
Step-up Transformer
EMF α N
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Step-Down Transformer
Secondary coil has fewer turns (N) than the primary.
EMFs Ns
---------- = --------
EMFp Np
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Power in a Transformer
If there are no losses (ideal transformer),
Powerprimary = Powersecondary
Power = voltage x current
EMFp x Ip = EMFs x Is
since voltage = EMF
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Step-up transformer: increases EMF, decreases current
Step-down transformer: decreases EMF, increases current
EMF α 1/I
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Electric Power Transmission
Power loss in wires occurs when current is high.
Use step-up transformer to transmit power at high emf and low current (minimize power loss).
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Electric Motor
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Motor: Converts electrical energy into mechanical energy.
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Commutators – switch the current direction in the armature coil every half turn
wire wrappings which turn
field poles
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In an A.C. motor, input electricity continually switches direction; commutators not needed.
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Maximum induced current whencutting through lines of magnetism
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With each ½ turn, wire in the armature changes its direction of motion in magnetic field.
Induced Alternating Current
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A.C. Generator
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D.C. Generator
To produce an output of D.C., use
commutators to switch current direction.
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Motor vs. Generator
Motor: converts electrical energy to mechanical energy
Generator: converts mechanical energy to electrical energy
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When a motor is spinning, it also acts as a generator and generates an EMF oppositethe supplied EMF.
This is called the back EMF.