ENGR225 Circuit Analysis Name_______________________________

**Lab
#6 - First Order RC and RL Circuits** Date________________________________

**Objectives:**

To see the actual voltage and current responses in first-order RC and RL circuits.

To see how our calculations agree with the observed responses.

**Procedures:**

1.
Use the LCR meter on the Cs & Rs
range to measure your capacitor for the circuit in Figure 1. The time constant will be the sum of the
three series resistors times the capacitance.
Build the RC circuit shown in Figure 1.
Set up the Wavetek for a 0-to-8V square wave __before__
you connect it to the circuit. *I will
show you how you can effectively observe this open circuit square wave even
after you connect the circuit.*
Adjust the frequency of the square wave so that the transient waveforms
are allowed to go to their final values after each square wave transition
(frequency = 500Hz). Record the current
waveform by measuring the voltage across the 51Ω resistor R and then
dividing the vertical scale by 51Ω to convert it to a current
waveform. Then interchange C and R and
record the voltage across C. __Obtain
scope pictures for both the current and the capacitor voltage waveforms when
the input is going from 0V to 8V and then when the input is going from 8V to 0V
(4 pictures).__

2. Calculate the expected capacitor voltage and current waveforms for part 1 right after the input voltage rises from 0V to 8V and then again when the input voltage drops from 8V to 0V. Compare your calculations with the measured waveforms by plotting the calculations in Mathcad on a similar time and amplitude scale or by plotting some calculated points right on the measured waveform displays. Either way compare and discuss the agreement between the calculated and measured waveforms.

3.
Use the LCR meter on the Ls & Rs
range to measure your values for the L and R_{L }(this is the Ls and Rs for the inductor) required for the circuit in Figure
2. Build the RL circuit of Figure
2. Set up the Wavetek
as in part one again choosing a frequency to allow the waveform to reach its
final value after each transition.
Measure the current waveform by measuring the voltage across the
51Ω resistor R and then dividing the vertical scale by 51Ω to convert
it to a current waveform. __Obtain
scope pictures for both the current and the inductor voltage waveforms when the
input is going from 0V to 8V and then when the input is going from 8V to 0V (4
pictures).__

4. Perform the same calculations for the voltage and current waveforms asked for in part 2 right after the input voltage changes from 0V to 8V and then again when the input voltage drops from 8V to 0V. Compare your results with the measured waveforms as before.

Note: the key points to compare between the calculated and measured waveforms are the initial values, the shape of the response curves, and the time it takes to reach the final values.