Teach lesson
Electronics Lab Essentials (3/7): measure resistance and voltage correctly
Students choose DMM resistance or DC-voltage mode, connect across the correct nodes, preserve the required powered state, and interpret units and signs.
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Learning Outcomes
Choose resistance or DC-voltage mode for a stated measurement.
Explain why resistance is normally measured on an unpowered circuit.
Connect a voltmeter in parallel across two powered nodes.
Interpret Ω, kΩ, V, mV, polarity, and an over-range/open indication.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
1 · One meter, two very different tests
6 min
A digital multimeter—or DMM—can measure several electrical quantities. That
does not mean the procedures are interchangeable.
For resistance, the meter sends a small internal test signal through an
unpowered component or network. For voltage, the meter observes the
potential difference between two nodes while the circuit is usually
operating. Selecting the wrong mode or powered state can produce a false
reading and may damage a physical meter or circuit.
A digital multimeter
On a future physical DMM, check three things together: the probe sockets, rotary or
button-selected function, and expected range. A correct screen symbol with a
lead in the wrong socket is still an incorrect setup.
You want to check the resistance of a loose resistor before placing it in a
circuit. Which setup is appropriate?
2 · Match quantity, connection, and powered state
7 min
Use these rules before touching a circuit:
### Resistance (Ω)
- Turn external power off. If capacitors or other energy-storage components are
present, use the laboratory's approved discharge method, then verify with the
DMM in DC-voltage mode that the relevant nodes are near 0 V before selecting
resistance mode. Never discharge a capacitor by directly shorting its leads.
- Isolate the component when other circuit paths could affect the reading.
- Place probes across the component or network.
- A finite reading describes opposition to the meter's test current. OL, OPEN, or an over-range symbol often means an open path or a value above the selected range; check the meter manual because displays vary.
### DC voltage (V⎓)
- Keep the circuit in the operating state you intend to examine.
- Place the voltmeter in parallel between the two nodes of interest.
- The display reports red-probe potential minus black-probe potential.
- A negative sign normally means the red probe is at the lower potential.
The connection changes with the quantity
This lesson uses the first two panels. Current measurement is shown for contrast
and is taught separately because it requires opening the circuit path and using
a current input socket.
Prefixes change the scale:
- 1 kΩ = 1000 Ω
- 1 MΩ = 1,000,000 Ω
- 1 V = 1000 mV
A meter displays 2.00 kΩ. Convert the reading to ohms, then explain the factor
used.
Why can a voltmeter be placed across two existing circuit nodes without opening
the normal current path, while an ohmmeter test should normally be done with
external power removed?
3 · Perform both tests on real hardware
10 min
You will use two saved Hive setups. The wiring and modes are already correct so
you can concentrate on the measurement logic. Hive shows the selected virtual
function, but it does not reproduce the physical act of placing leads in the
COM and V/Ω sockets or checking a manual range. Those are optional theory in
this lesson and must be practiced later only with the actual meter's instructions
and appropriate supervision.
Resistance test: unpowered 2 kΩ network
Open Hive from this block and wait for two
1 kΩresistors to appear.Confirm that no DC supply wire powers the measured resistor path.
Open the Multimeter and confirm resistance (
Ω) mode.Predict the series total:
1 kΩ + 1 kΩ = 2 kΩ.Select Perform Measurement (
Realizar mediciónin Spanish) once.Record the displayed number and unit in the resistance row below.
Voltage test: +5 V relative to ground
Open this saved setup and locate the supply and ground connections.
Open the Multimeter and confirm DC-voltage (
V⎓) mode.Predict a positive reading near
5 Vbecause the red side is at the higher potential.Select Perform Measurement once.
Record the signed number and unit in the voltage row below.
Complete exactly two rows. The External power during test column checks the
procedure, not merely the result. Format-only example: the first row could
read `Two 1 kΩ resistors in series | resistance (Ω) | off / not applied | 2.02 |
kΩ. Replace 2.02` with your own result. Leave extra blank rows unused.
DMM mode comparison
Complete the two fixed rows after their Hive measurements. Record selected mode, whether external power is applied to the measured network, the signed displayed value, and unit.
| Test | DMM mode | External power during test | Displayed number | Displayed unit |
|---|---|---|---|---|
Compare the two procedures using your evidence. State the mode, powered state,
connection purpose, and approximate result for each test.
4 · Optional theory: diagnose a physical DMM setup
7 min
No physical DMM is required. For a future supervised lab, practice saying
the complete measurement aloud:
> quantity → mode → sockets → powered state → probe nodes → expected scale → unit
For example: “DC voltage, V/Ω socket and COM socket, circuit powered, red probe
at the output, black probe at ground, expecting about five volts.” This short
habit catches many first-lab mistakes.
In a hypothetical later lab, a physical meter in resistance mode displays an
open/over-range indication for a resistor expected to be 1 kΩ. Which are
sensible power-off checks? Select all that apply.
Using only the theory above, write a one-line setup statement for measuring the
voltage across a powered resistor in a hypothetical future physical lab.