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Topics
Points of Emphasis
Prerequisites
Lab Activities
Gives an overview of AC circuits. In particular, the following theoretical
predictions concerning AC circuits are checked by the student:
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the current in a circuit and the voltage across a resistor are always "in
phase";
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the current in a circuit leads the voltage across a capacitor by 90
degrees;
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the current in a circuit lags behind the voltage across an inductor by 90
degrees;
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the ratio of the voltage across a capacitor to the capacitive reactance,
1/wC, gives the current in that circuit element;
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the ratio of the voltage across an inductor to the inductive reactance, wL,
gives the current in that circuit element;
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for an LRC circuit with a square wave driving voltage:
a. when R < 2*(L/C)1/2, the current oscillates with an angular frequency given
by w = (1/L*C)1/2;
b. when R = 2*(L/C)1/2, the current does not oscillate but rather returns to
zero in the fastest possible time; and
c. when R > 2*(L/C)1/2, the current does not oscillate but rather returns to
zero slower than the critically damped case.
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for an LRC circuit with a sine wave driving voltage:
a. when w2 << the natural oscillating frequency squared, wo2, the current
leads the driving voltage by approximately 90 degrees;
b. when w2 = wo2, the current is in phase with the driving voltage; and
c. when w2 >> wo2, the current lags behind the driving voltage by
approximately 90 degrees;
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a plot of the angular frequency of the driving voltage vs the current is
that of a typical resonance curve; and
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the ratio of the driving voltage to the impedance gives the current in the
circuit.
Quantitative results tend to be within 10% of the theoretically predicted values.
Course Level
Introductory level - P4, P14, P16
Student Handouts
Equipment
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Number of set-ups available: 20
Per lab station:
1 oscilloscope
1 function generator
1 frequency counter
1 multimeter
1 resistance substitution box
1 capacitance substitution box
1 inductor
8 banana leads
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Notes
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