 Applications of Electromagnetism

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Applications of Electromagnetism

Electromagnetic Waves

A changing magnetic field generates an electric field.
B  E A changing electric field generates a magnetic field. E  B

changing E changing B changing B changing E ELECTROMAGNETIC WAVE
speed = c (speed of light; 3.00 x 108 m/s)

EM Wave

v E ┴ B ┴ v

To produce an EM wave: EM waves produced by accelerated electric charges.

Electromagnetic Spectrum
v = λ f

Transformers

A changing magnetic field in the primary coil induces a current in the secondary coil.

Use an alternating current to produce a constantly
changing magnetic field.

EMF in a coil depends on the number of turns of wire in that coil.
Step-up Transformer EMF in a coil depends on the number of turns of wire in that coil. EMF α N

Step-Down Transformer
Secondary coil has fewer turns (N) than the primary. EMFs Ns = EMFp Np

If there are no losses (ideal transformer),
Power in a Transformer If there are no losses (ideal transformer), Powerprimary = Powersecondary Power = voltage x current since voltage = EMF EMFp x Ip = EMFs x Is

EMF α 1/I Step-up transformer: increases EMF, decreases current Step-down transformer: decreases EMF, increases current

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).

Electric Motor

Motor: Converts electrical energy into mechanical energy.

Commutators – switch the current direction in the armature coil every
wire wrappings which turn field poles Commutators – switch the current direction in the armature coil every half turn

In an A.C. motor, input electricity continually switches direction; commutators not needed.

Maximum induced current when
cutting through lines of magnetism

Induced Alternating Current
With each ½ turn, wire in the armature changes its direction of motion in magnetic field.

A.C. Generator

D.C. Generator To produce an output of D.C., use commutators to switch current direction.

Motor: converts electrical energy to mechanical energy
Motor vs. Generator Motor: converts electrical energy to mechanical energy Generator: converts mechanical energy to electrical energy

When a motor is spinning, it also acts as a generator and generates an EMF opposite
the supplied EMF. This is called the back EMF.