HPP Activity 60v2
Going Around a Loop
In order for an electrical signal to be transmitted, whether it be a nerve signal within the
human body, an electrical signal between two computers, or the electricity that powers the
lights of your house, there must be a closed circuit. You will now conduct a series of
quantitative measurements to gain a better understanding of how circuits behave.
Task #1 - An Introduction to Two New Tools
Your instructor will briefly introduce two new measurement tools: an analog ammeter
and a digital multimeter. You will use these tools to investigate the properties of a variety of
circuit configurations during this lesson. These tools are also discussed on the separate
reference sheet.
1.
Write a brief summary of each tool in your logbook. Describe its name, what it measures,
and how to use it correctly. Be sure to note the correct orientation of the meter when
placing it in a circuit.
2.
Using the DMM set to measure resistance, measure and record the resistance of your body
in the following ways:


In general you should never place your body into a circuit!
Make certain that the multimeter is not connected to anything before you try
this experiment.
(a)
(b)
(c)
Across two points of your palm.
Across two points on your arm.
Between your two palms.
(d)
Describe how these results help to account for your results in the mini-experiments
conducted last week with the chirping toy. What does this tell you about the
resistance of human skin?
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 1 of 10
HPP Activity 60v2
Using A Digital Multimeter to Measure Voltage
To measure the potential difference (V) between two points
with the digital multimeter:





Make sure that the voltage (V) button is pressed.
Set the scale to its maximum value (1000 V).
Place the two leads of the DMM on either side of the
component you wish to measure. Place the high (+)
lead on the positive terminal and the low (-) lead on
the negative terminal.
Adjust the scale to an appropriate range.
Record the value.
High
+
DMM
Low
-
V
Measuring the potential
difference V across a battery
Using a Digital Multimeter to Measure Resistance
To measure the resistance () of something:





Press the resistance () button on the DMM.
Set the scale to its maximum value (20M).
Place the two leads of the DMM on either side of the
component you wish to measure. Make sure the
component is isolated. That is, nothing should be
connected to the component except the two leads of the
DMM.
Adjust the scale to an appropriate range.
Record the value.
Low
-
DMM

High
+
Resistance
R
Measuring the resistance R
of a circuit element
Using An Analog Ammeter to Measure Current
Current flow is measured in units of amperes where 1 Ampere = 1 A = 1 C/s. Current
can be measured by an instrument called an ammeter.
When connecting the ammeter into a circuit, make
certain that the lead connected to the negative terminal of
the battery connects to the negative (COM.) terminal of the
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 2 of 10
HPP Activity 60v2
ammeter. To measure the current flowing through a circuit,
the ammeter must be connected directly into the circuit, in
series with another component. That way, all the current
flowing through the component of interest will flow through
the meter!
For our ammeters, each red terminal is labeled with
the maximum current it can measure. Currents larger than
the labeled values can damage the meter, so always start
measuring currents using the terminal with the largest
rating (5 A). If the pointer moves to the extreme right at any
R2
R1
R
3
+
-
(red) +
A
Com. -
Using an ammeter to measure the
current I1 through R1
time, disconnect the meter (or the battery) immediately to avoid damage.
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 3 of 10
HPP Activity 60v2
Task #2 - Measuring Potential Differences and Currents
Equipment:
Digital multimeter (DMM), Ammeter, 4 D-cell battery set, Wood block with mini
sockets, Bulb #46 (red base), Bulb # 40 (blue base), Key switch, Banana leads
Experiment #1 – Two non-identical bulbs in series
A
Build the following circuit using two bulbs,
four D-cell batteries, and a key switch.
+
#40
B
#46
Circuit with two non-identical bulbs in series
C
3.
Close the key switch and carefully observe the behavior of the two bulbs. Describe and
compare the brightness of each of the bulbs.
Discuss in your group the following prediction questions.


How would the potential difference across the #40 bulb and across the #46 bulb (if the
switch were closed) compare to the potential difference across the batteries?
How would the current measured at points A, B, and C be related to each other (if the
switch were closed)? Which currents would be largest, smallest, and/or identical?
Data Collection - Experiment #1
You will now test your predictions by completing the following procedures. Be sure to
close the key switch whenever you are taking a measurement. However, open the key switch
any time you are not taking a measurement (to preserve the life of the batteries!).

Carefully draw a picture of the circuit so you can clearly label what you are measuring.

Using the DMM, measure the following three potential differences: across the battery set,
across the #40 bulb, and across the #46 bulb. Label and record these values as VBatt=VAC,
V#40=VAB, and V#46=VBC.

Using the ammeter, measure the current flowing through the following three locations: A, B,
and C. Label and record these values as IA, IB, and IC.
4.
Quantitatively compare the values of the three potential differences that you measured.
How do they appear to be related? If possible, write an equation relating the values
(i.e., VAC = …). How well does this result match your prediction?
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 4 of 10
HPP Activity 60v2
5.
Quantitatively compare the values of the three currents that you measured. How do they
appear to be related? If possible, write an equation relating the values (i.e., IA = …). How
well does this match your prediction?
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 5 of 10
HPP Activity 60v2
Experiment #2 – Two non-identical bulbs in parallel
A
Build the following circuit.
+
B
C
#46
Circuit with two non-identical bulbs in parallel
#40
D
6.
Close the key switch and carefully observe the behavior of the two bulbs. Describe and
compare the brightness of each of the bulbs. Compare the result to what you observed
when the bulbs were in series.
Discuss in your group the following prediction questions.


How would the potential difference across the #40 bulb and across the #46 bulb (if the
switch were closed) compare to the potential difference across the batteries?
How would the current measured at points A, B, C, and D be related to each other (if
the switch were closed)? Which currents would be largest, smallest, and/or identical?
Data Collection - Experiment #2
You will now test your predictions by completing the following procedures. Be sure to
close the key switch whenever you are taking a measurement. However, open the key switch
any time you are not taking a measurement (to preserve the life of the batteries!).

Draw a picture of the circuit so you can clearly label what you are measuring.

Using the DMM, measure the following three potential differences: across the battery set,
across the #40 bulb, and across the #46 bulb. Label and record these values as VBatt=VAD,
V#40=VCD, and V#46=VBD.

Using the ammeter, measure the current flowing through the following four locations: A, B,
C and D. Label and record these values as IA, IB, IC, and ID.
7.
Compare the values of the potential differences that you measured for this parallel circuit.
How do they appear to be related? Write an equation relating the three values.
8.
Compare the values of the currents that you measured. How do they appear to be
related? Write an equation relating the four values.
9.
Based on your data, describe how series and parallel circuits seem to be similar and how
they seem to be different.
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 6 of 10
HPP Activity 60v2
10.
The word "resistance" is used to quantify how much of an obstacle a component adds to
current flow through a circuit. Based on this description, which light bulb seems to have
the greater resistance? Describe your reasoning.
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 7 of 10
HPP Activity 60v2
Task #3 - Using Resistors in Place of Light Bulbs
Equipment:
Digital multimeter (DMM), Ammeter, 4 D-cell battery set, Plastic circuit block,
Three assorted resistors, Key switch, Banana leads
R1
Build the following
circuit with the three provided
resistors and the plastic circuit
block. Be sure each resistor is
securely fastened to the circuit
clock.
A
B
+
R2
-
R3
C
D
E

Carefully draw this circuit in your logbook including the corresponding labels (R1, R2, R3, A,
B,…).
11.
What elements in this circuit appear to be in parallel? Explain.
What elements of this circuit appear to be in series? Explain.
12.
Discuss and answer the following prediction questions:
(a) Based on your earlier experiments, predict two voltage values in this circuit that will
have the same value. Explain your reasoning.
(b) Based on your earlier experiments, predict two current values in this circuit that will
have the same value. Explain your reasoning.
Using the provided equipment, test your two predictions and record their results. If
your predictions were not correct, try to adjust your reasoning accordingly and explain your
new conclusions.
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 8 of 10
HPP Activity 60v2
Be sure to answer the following items as you write your Implications section to this
week's lab. Based on your results for the different circuits…




Write a rule that describes the potential differences that can be found when circuit
components are in series with each other.
Write a rule that describes the currents that can be found when circuit components are
in series with each other.
Write a rule that describes the potential differences that can be found when circuit
components are in parallel with each other.
Write a rule that describes the currents that can be found when circuit components are
in parallel with each other.
End of Lab Cleanup
Complete the following before you leave…
 Turn off the multimeter.
 Unplug all banana leads.
 Return the three resistors to the box provided at your station.

Be sure to read pages 2-3 of Lesson 63 before the start of the next lab!
Introduction to A New Tool: Resistor Color coding
Resistors are circuit elements that have been manufactured to have a specific value of
resistance within a given tolerance (say, within  5%). To assist in the easy identification of
resistors, the industry has adopted a color code system to identify the resistance values.
Sample Resistor:
Resistor Color Code Scheme
Blue Green Red Gold
6
5
2
5%
R = 65 x 10 2   5%
R = 6500   325 
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 9 of 10
HPP Activity 60v2
silver
Last (fourth) band = Tolerance
Gold ± 5%
Silver ±10%
None ±20%
gold
-2
-1
black
0
brown
red
1
2
orange
yellow
3
4
green
blue
5
6
violet
gray
7
8
white
9
Activity Guide
 2010 The Humanized Physics Project
Supported in part by NSF-CCLI Program under grants DUE #00-88712 and #00-88780
Page 10 of 10