Lab #2
First Order Circuits
Due: End of THIS Lab Session
Name / SN:____________________________________
TA:
__________
Name / SN:____________________________________
TA:
__________
A) Pick up the following components from the TA:
1.
2.
3.
4.
100 resistor (1)
1K resistor (1)
100nF capacitor (2)
100mH inductor (1)
B) Connect the capacitor and 1K resistor in series with a 5V power supply.
1.
Measure the voltage across the resistor and capacitor and compute the current in the circuit.
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Resistor
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Capacitor
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Current
C) Replace the power supply with a signal generator. Set the signal generator to a
5Vpeak, 300Hz square wave. Adjust the offset so that Vmin=0. Adjust the duty
cycle so that the signal stays high for 1ms. Use one scope probe to display the
input signal and the other scope probe to display the voltage across the
capacitor.
TA: ____________________________________
1.
Compute the time constant. Read the time constant from the scope.
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Computed 
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Measured 
ECE 251 - Circuit Analysis I
Department of Electrical & Computer Engineering, UBC
2.
Reduce the duty cycle as much as possible and adjust the frequency so that the on time is
equal to 1x the computed time constant. Record the maximum voltage measured across
the capacitor. Compute the percentage of the steady state voltage (the voltage across the
capacitor if it were given a very long time to charge up).
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Voltage
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Percentage
D) Use the RCL meter to measure the actual inductance of the inductor and the
Multimeter to measure the resistance of the inductor. Replace the resistor and
capacitor with the 100 resistor and the inductor. Repeat steps B and C.
TA: ____________________________________
1.
Compute and measure all of the corresponding values.
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Inductor Inductance
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Inductor Resistance
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Resistor
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Inductor
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Current
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Computed 
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Measured 
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Voltage
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Percentage
2.
In this circuit, is it reasonable to model the inductor as an ideal inductor? Propose a more
accurate ideal circuit model. Recompute using your new model.
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Better Model
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Computed 
ECE 251 - Circuit Analysis I
Department of Electrical & Computer Engineering, UBC
E) Make a voltage divider out of the two capacitors. Drive it with a 5Vpeak, 20KHz
square wave. Use one scope probe to display the input signal and the other
scope probe to display the voltage between the two capacitors.
TA: ____________________________________
1.
Sketch the input waveform with the voltage divider connected and dis-connected.
Explain why the two are not the same and whether or not capacitors make a good voltage
divider.
2.
Theoretically, you can also make a voltage divider out of two inductors. Would this make
a better or worse voltage divider than 2 capacitors? Explain (assume near ideal behaviour).
ECE 251 - Circuit Analysis I
Department of Electrical & Computer Engineering, UBC