Adnan Menderes University
Elec. & Electronics Eng. Dept.
EE209 Circuit Laboratory I
2015-2016
Experiment 8
First Order Circuits
OBJECTIVES
In this experiment, you will learn:
1. Observing the both voltage across and current through a capacitor while it is charging and
discharging by using DSO.
2. Observing the both voltage across and current through an inductor by using DSO.
3. Measuring the time constant of an R-C and R-L circuit.
EQUIPMENT LIST
1. Power Supply
2. Digital Storage Oscilloscope (GW Instek GDS-1072A-U)
3. Function/Arbitrary Waveform Generator (AATech AWG 1020A)
4. Breadboard
5. Carbon resistor: 1 kΩ
6. Capacitor: 100 nF
7. Inductor : 100 mH
PRELIMINARY WORK
1. Study the basic principles of natural and step responses of capacitors and inductors
regarding the first order circuits.
2. Plot the expected outputs of the R-C and R-L circuits when the input voltage is a
square wave.
3. What is the time constant (τ) for the R-C and R-L circuits? Explain the relationship
between τ and charging or discharging times of the capacitor and inductor.
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EXPERIMENTAL WORK
R-C Circuit
1. Build up the circuit given in Fig. 8.1 with
, C=100 nF. Apply VPP=10V and
f=500 Hz square wave from the function generator, observe and plot vin(t) and vout(t)
simultaneously by using DSO.
2. What is the final voltage across the capacitor when it is fully charged? Compare it with
the supply voltage, is it same? Explain.
3. What is the voltage across the capacitor when it is fully discharged? Is it zero? Explain.
4. Measure time constant (τ) for the R-C circuit from the vc(t) graph and record your
measurement as obs.
obs = ……………………
Is this observed τ (obs) consistent with the calculated (theoretical) time constant (cal)?
Explain.
5. How many time constants did it take for the capacitor to reach full charge? Full
discharge?
Fig.8.1 R-C Circuit
6. Repeat the steps 1-3 for an input signal with VPP=10V and f=5 kHz square wave.
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R-L Circuit
To analyze the R-L circuit, the circuit given in Fig. 8.1 is used again by replacing “C” with “L”.
7. Build up the R-L circuit by using “L” instead of “C” in circuit given in Fig. 8.1. Observe
and plot the voltage across a resistor R by using DSO. (f=50 kHz)
8. Plot the inductor current (IL) by using your measurement in previous step (Hint: what is
the relationship between the inductor current and resistor current?) What is the maximum
and minimum values of inductor current? Compare the experimental results with the
expected value of the inductor current.
9. Measure time constant (τ) for the R-L circuit from the VR(t) graph and record your
measurement as obs.
obs = ……………………
Is this observed τ (obs) consistent with the calculated (theoretical) time constant (cal)?
Explain
10. What is the minimum and maximum inductor voltages?
11. Repeat the steps 7 and 8 for an input signal with VPP=10V and f=200 kHz square wave.
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