How to use a MULTIMETER in a simple circuit
A
i
∆V
+
Measuring current at
this position in series
-
AMMETER
∆V
R
V
Measuring voltage at
this position in parallel
i
VOLTMETER
To measure the VOLTAGE:
Set your multimeter to a voltmeter and select the range to the highest value
possible. Note: the probes of the multimeter have to be inserted in the V and
COM inputs.
To measure voltage across a resistor, place the voltmeter in parallel with the
resistor.
To measure the CURRENT:
Set your multimeter to an ammeter and select the range of measurements to
1 A initially. Note: the probes of the multimeter have to be inserted in the A
and COM inputs.
To measure current in parts of a circuit, the connections must pass through
the ammeter.
To measure the RESISTANCE:
Set your multimeter to an ohmmeter and select the range to the highest
value possible. Note: the probes of the multimeter have to be inserted in the
Ω and COM inputs.
Make sure the resistor is NOT CONNECTED in the circuit when using the
ohmmeter.
Each group was given a resistor. Determine its resistance value using the
ohmmeter mode of the multimeter.
Build a circuit based on the circuit diagram presented before, measure the
current for different voltages.
Start your measurements with the variable DC power supply set at 0 V and
make at least ten measurements between 0 and 15 V.
Make a plot of V vs. i, and calculate the slope (slope = ∆Y/∆X for Y vs. X plot).
Is the plot linear?_____________________
How much is the slope (write down the units!) ? ____________________
Voltage across
resistor
( )
Value of the
resistance
measured
with the
ohmmeter:
___________
Current
( )
Circuit in Series
Select 3 resistors of known resistance, and connect them in series such as the circuit
shown in the diagram below.
+
DC
supply
B
A
R2 =_______Ω
R1 =_______Ω
-
C
MEASURING THE CURRENT AT POINTS A, B, C, D:
Set the function A (for ammeter) in your multimeter, and the range to 200 mA.
Break the circuit at A, B, C, or D by disconnecting one at a time. Connect the red probe of
the multimeter to the part of the circuit that is closest to the potential source. The black
probe of the multimeter (inserted into the COM input of the multimeter) is then connected
to the remaining side, closing the circuit.
Use the DC power source to supply about 10 V across the circuit in series. Lower the
range scale in the multimeter to read an appropriate current value if needed. Fill in table 1.
MEASURING THE VOLTAGE ACROSS EACH RESISTOR:
Set the function V (for voltmeter) in your multimeter, choose DC current (
range to 20 V.
), and the
Set the probes of the multimeter across the voltage source and record the voltage of the
supply (Vtot).
Now place the probes across each resistor and record their potential drop. Lower the
range scale to a more sensitive range if necessary. Fill in table 2.
Table 1
Table 2
iA
Vtot
iB
VR1
iC
VR2
Answer these questions in your lab report:
What is the equivalent resistance of this circuit? __________
Do you find that VR1+VR2 = Vtot ? _________ Should you? Why/why not?
Using Ohm’s Law, what should be the electric current in this circuit? __________
Do you find that iA = iB = iC ? _________ Should you? Why/why not?
Circuit in Parallel
Select the same 3 resistors from the previous exercise, and connect them in parallel such
as the circuit shown in the diagram below.
+
DC
supply
-
itot
i1
A
i2
R1
D
itot
R2
C
B
MEASURING THE CURRENT AT POINTS A, B, C, D, E:
Set the function A (for ammeter) in your multimeter, and the range to 200 mA.
Break the circuit at A, B, C, D, or E by disconnecting one at a time. Connect the red probe
of the multimeter to the part of the circuit that is closest to the potential source. The black
probe of the multimeter (inserted into the COM input of the multimeter) is then connected
to the remaining side, closing the circuit.
Use the DC power source to supply about 10 V across the circuit in series. Lower the
range scale in the multimeter to read an appropriate current value if needed. Fill in table 1.
MEASURING THE VOLTAGE ACROSS EACH RESISTOR:
Set the function V (for voltmeter) in your multimeter, choose DC current, and the range to
20 V.
Set the probes of the multimeter across the voltage source and record the voltage of the
supply (Vtot).
Now place the probes across each resistor and record its potential drop. Lower the range
scale to a more sensitive range if necessary. Fill in table 2.
Table 1
i tot A
i1
i2
itot D
Table 2
Vtot
VR1
VR2
Answer these questions in your lab report:
What is the equivalent resistance of this circuit? _________
Do you find that i1+i2 = itot ? _________ Should you? Why/why not?
Using Ohm’s Law, what should be the total voltage across this circuit? _________
Do you find that VR1 = VR2 = Vtot ? _________ Should you? Why/why not?
Lab Report:
-Cover page
-You can attach all the previous pages completed (show the
values of the resistances). Show a drawing of the circuits and
the values of the resistances, in case you choose to write your
own information instead of just attaching pages. Remember to
answer any and all questions in your lab report in an organized
way.
-Graph
-Write a final page containing any and all calculations you’ve
done, and an analysis table, where you will compare the slope of
the graph with the formal value for the resistance given to your
group (assume formal value = value measured by ohmmeter).
You should always calculate the % difference. On the same
page, write a conclusion paragraph.