DC Circuits
Part I. Equivalent resistance
1. Use the Digital Multimeter (DMM) in the ohmmeter mode and measure the resistance of R1,
R2, and R3.
question 1. How well do the actual measured values agree with the values claimed by the color
code? Give % differences.
2. Arrange the three resistors in series.
Use the DMM to measure the total or
R2
R1
R3
equivalent resistance of the combination.
question2. Compute the theoretical value of the series combination based on the individual
values you measured previously. Compare by giving the % difference.
3. Arrange the resistors in parallel and measure the equivalent
resistance.
question 3. Compute the theoretical value of the combination based on
the individual values you measured previously.
Compare to the measured value by giving the % difference.
R1
R2
R3
4. Arrange the three resistors in some other pattern. Record the schematic of your layout.
Measure the equivalent resistance.
question 4. Compute the theoretical value of the combination.
Compare to the measured value by giving the % difference.
Part 2. Circuits
R1
1. Construct the circuit shown.
2. Use the DMM in the DC volts mode to set the DC power
supply (red and black jacks at the end of the lab table) to 15 volts.
R3
3. Measure the potential across each resistor.
4. Record the current using the ammeter. Remember, you need to break the circuit and insert the
ammeter in series. To avoid blowing a fuse, ask your instructor if unsure how to connect the
ammeter.
question 5. Do your potential measurements support Kirchhoff's voltage law?
What is the sum of the potential increases and decreases around the loop?
question 6. Using the 15 volt setting and the values of the resistors, compute the expected current
and compare to the measured value.
question 7. Change the position of the ammeter to the location between the resistors R2 and R3.
Comment on your findings.
MEASURING ELECTRICAL POTENTIAL
The Oscilloscope & Digital Multimeter
1. Become familiar with the o-scope's functions.
Use channel one to look at a signal from the function generator. Manipulate the controls and
observe the changes. Take note of the volts per division (VOLTS/DIV) that applies to the
potential of the vertical scale and the seconds per division (SEC/DIV) that applies to the
horizontal scale. Frequently in electronics, the electron beam must be swept across the CRT
(Cathode Ray Tube) screen rapidly, so the time settings are often in the millisecond (ms) or
microsecond (µs) range.
2. Measure an ac voltage.
Use the DMM in the ac volts mode to measure the ac potential from the power supply (yellow
terminals at the end of the lab table). Then measure the same voltage using the o-scope. Record
the peak to peak voltage with the o-scope. Since ac voltmeters give the root mean square
voltage, you need to change to rms:
Vrms =
Vp ! p
2 2
Compare by giving the % difference.
3. Determine the frequency of an ac voltage.
Use the o-scope to measure the period of the ac voltage of the power supply (yellow terminals).
Compute the frequency (f=1/T) and compare (% difference) to the standard value (60 Hz).
4. Look at the operation of a diode.
Construct the circuit shown. If your instructor uses the function generator rather than the table
power supply (yellow terminals), be sure to keep the frequency below a couple of kilohertz to
see the proper diode behavior. The o-scope measures the voltage across the resistor. So the
waveform is not distorted, be sure to use DC and not AC coupling. Sketch the waveform. Note
that the diode conducts in only one direction.
diode
oscilloscope trace