PHYS 102

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PHYS 102

• Where

T is the period of oscillation.
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PHYS 102

• Transformers
• One symbol used to denote a transformer is

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PHYS 102

• Transformers
• Looks like two solenoids in close proximity to
  one another.

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PHYS 102

• Transformers

If primary current is alternating in time, then
the magnetic flux in transformer core is
changing! Induced EMF
VP NP(Induced EMF) VS NS(Induced EMF) same
induced EMF
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PHYS 102

• Transformers

Remember Power input must equal power output
(Always)
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PHYS 102

• Transformers

Have we all seen a transformer?
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PHYS 102

• How do the other circuit elements behave under
  the influence of an AC source?
• Remember, everything in the past has been
  analyzed with a DC source.

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PHYS 102

• Resistors

We say that the current is in phase with the
driving voltage.
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PHYS 102

• Capacitors

We say that the current is out of phase with
the driving voltage. Current in a capacitor
leads the voltage by 90o.
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PHYS 102

• Capacitors

Since the sine function has a maximum value of 1,
we could define a peak current.
Resembles current through resistor.
XC is called the reactance of a capacitor.
Units Ohms. The slower the frequency the
greater the capacitive reactance. Low
frequencies? capacitor acts like open
circuit. High frequencies? capacitor acts like
short circuit.
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PHYS 102

• Capacitors

XC is not the same as Resistance because no power
is dissipated through a capacitor.
Current leads driving voltage it takes current
to move charge on the capacitor plates?current
must flow before the voltage can change
significantly.
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PHYS 102

• Inductors

We say that the inductor current is out of
phase with the driving voltage. Current in an
inductor lags behind the voltage by 90o.
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PHYS 102

• Inductors

XL is called the reactance of an inductor.
Units Ohms. The greater the frequency the
greater the inductive reactance. Low frequencies?
inductor acts like short circuit. High
frequencies? inductor acts like open circuit.