april 26 th, 2006 ac circuits phys 102 where t is the period of oscillation
TRANSCRIPT
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April 26th, 2006 AC Circuits
PHYS 102Where
T is the period of oscillation.
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April 26th, 2006 AC Circuits
PHYS 102Transformers:
One symbol used to denote a transformer is:
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April 26th, 2006 AC Circuits
PHYS 102Transformers:
Looks like two solenoids in close proximity to one another.
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April 26th, 2006 AC Circuits
PHYS 102Transformers:
VP= NP(Induced EMF); VS= NS(Induced EMF); same induced EMF
S PN NCalled step-up transformer
P SN NCalled step-down transformer
If primary current is alternating in time, then the magnetic flux in transformer core is changing!
Induced EMF
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April 26th, 2006 AC Circuits
PHYS 102Transformers:
Remember: Power input must equal power output (Always)
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April 26th, 2006 AC Circuits
PHYS 102Transformers:
Have we all seen a transformer?
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April 26th, 2006 AC Circuits
PHYS 102How 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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April 26th, 2006 AC Circuits
PHYS 102Resistors:
We say that the current is “in phase” with the driving voltage.
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April 26th, 2006 AC Circuits
PHYS 102Capacitors:
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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April 26th, 2006 AC Circuits
PHYS 102Capacitors:
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.
Resembles current through resistor.
Since the sine function has a maximum value of 1, we could define a peak current.
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April 26th, 2006 AC Circuits
PHYS 102Capacitors:
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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April 26th, 2006 AC Circuits
PHYS 102Inductors:
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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April 26th, 2006 AC Circuits
PHYS 102Inductors:
I tV
Ltp( ) sin( )
2
IV
L
V
XPp p
L
X LL
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.