Description
Please write all the words in red into your own word, and draw the chart again.
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Alessandro
Experiment
Daniel
1
Sunny
Electrostatics
INTRODUCTION
Charge, like mass, is a fundamental property of matter. However, unlike mass, which seems to be
more or less unchanging, the effects of charge are not always apparent. In fact, we use terms like
“charged” or “uncharged” to describe objects when we would not think of using parallel descriptors
for mass. In this experiment, you will observe charge separation and transfer and learn how to
measure the electric charge of objects.
OBJECTIVES
In this experiment, you will
• Use a Charge Sensor and Faraday Pail to measure electric charge.
• Observe and quantify the separation of electrical charge by friction.
• Observe and quantify charging by contact.
• Observe and quantify charging by induction.
MATERIALS
Vernier data-collection interface
Logger Pro or LabQuest App
Vernier Charge Sensor
Faraday Pail and Cage
grounding plane
two wires to ground objects
grounding wrist strap
charge separators
cotton cloth
You will use a Charge Sensor and a Faraday Pail to measure the sign and magnitude of the
electrostatic charge in these activities. This combination of equipment is capable of measuring very
small amounts of charge, which can be accidentally introduced into your experiment. It is important
to know how and when to discharge the sensor and when to ground objects in order to obtain
satisfactory data.
You should perform Part 1 and discuss your findings before proceeding with the rest of the
experiment.
PART 1 THE STATIC ELECTRICAL CHARGE ON YOUR BODY
PROCEDURE
This part of the experiment demonstrates the quantity of charge that can reside on your body and
how you can minimize the effects of this build-up of charge in subsequent experiments.
1.
Set up the Faraday pail and charge sensor as shown in Figure 1.
a. Place the plastic disk that holds the Faraday pail and cage on the grounding plane.
b. Place the Faraday pail and the cage on the disc.
Figure 2
c. Connect the black lead from the charge
sensor to the grounding plane.
d. Connect the red lead from the charge
sensor to the Faraday pail.
e. Connect the charge sensor to the datacollection interface and set the range
switch to the +/- 10 V position.
Figure 1
f. Connect a grounding wire between the cage
and the grounding plane.
g. This equipment is capable of measuring
very small amounts of charge. As you
proceed with the experiment, your
equipment may accidentally or
intentionally develop a charge. It will be important to remove or ground unwanted charge
either in the Faraday pail or on the sensor. This is accomplished by pressing and holding the
Reset button on the sensor.
h. You are now ready to measure the charge of objects that are inserted into the center of the
Faraday pail.
2.
Scuff your shoes on the floor or carpet. (Note: Do not use the grounding strap yet.) Insert a
finger into the pail without touching the pail or cage. Observe the readings on the meter.
3.
Remove your finger. Again, observe the readings on the meter. Record your findings.
4.
Touch the metal grounding plane that holds the Faraday pail with your finger.
5.
Insert your finger into the pail without touching the pail. Observe the reading on the meter.
Remove your finger. Again, observe the reading on the meter. Account for your observations.
6.
7.
If possible, repeat Steps 2 and 3 using a different combination of shoe type or flooring
(perhaps your lab partner has a different type of shoe).
Ground the pail and zero the sensor by pressing and holding the Reset button on the sensor.
8.
Attach the alligator clip on the grounding strap to the grounding plane and attach the
grounding strap to your wrist.
9.
Repeat Steps 2 and 3. (Note: This time you will use the grounding strap.) Make a record of
your observations in your lab notebook.
Describe the reading of the charge sensor when you placed your finger in the Faraday pail
and then removed it. How do your findings compare with others in the class?
PARTS 2–4 THE SEPARATION AND MOVEMENT OF CHARGE
PROCEDURE
For the remainder of this experiment you will collect charge data as a function of time. During your
analysis you will identify events on the graph (e.g., when an object is inserted into or removed from
the pail) using features in the software called Data Marks and Data Tags. Data Marks and Data Tags
are both ways to add a note to a particular moment in data collection, but Marks are added during
data collection only. During data collection, press a key or tap an icon to mark an event. The time
and associated sensor value is noted; later, you can add notes to that event.
Mark Data in Logger Pro
a. While collecting data in Logger Pro, press the “D” key on the keyboard for each point of
interest. Each time an event is marked, a Data Mark helper object will be displayed on the
graph.
b. When data collection is complete, double-click each Data Mark helper object and enter a
description for the event.
c. If you wish to add additional tags after you have stopped data collection, you may insert a
Data Tag. Turn on the Examine tool. Click the point on the graph you wish to tag and choose
Tag Data from the Experiment menu or press “D.” A Data Tag helper object will appear.
Part 2 Charge separation due to friction
In Part 1, you explored the charge that accumulated on your body, but you did not explore the
charge that might be on the floor or carpet. If you were able to measure the charge on the floor,
what would you expect to observe? In this part of the experiment, you will use small dissimilar
materials to explore the charge on each of them after they are rubbed together.
1.
Choose New from the File menu. Change the data-collection duration to 60 seconds and the
data-collection rate to 10 Hz.
2.
Attach the alligator clip on the grounding strap to the grounding plane, and then attach the
grounding strap to your wrist. Ground the system and discharge the charge sensor by pressing
and holding the Reset button on the sensor.
3.
To remove any charge from the charge separators, dab each charge separator on a damp
cotton cloth. Do not rub the charge separator and cotton cloth together, as this might result in a
build-up of charge on the disc. Insert the charge separators into the Faraday pail one at a time to
verify that they are electrically neutral.
4.
Rub the white and gray charge separators together, then hold them separately.
5.
In the next step, mark each time you insert or remove the charge separator.
6.
Start data collection; be ready to mark events. Insert the white charge separator into the
middle of the pail without touching the pail. Wait 4 or 5 seconds, then remove it. Wait a couple
of seconds, then insert the gray charge separator into the middle of the pail and wait 4 or 5
seconds. Remove it and wait a couple of seconds. Finally, position both charge separators in the
pail; be careful to keep the charge separators from touching the pail or each other. Wait 4 or 5
seconds, then remove both separators and stop data collection.
7.
Label the marked events for each of the charge separators. Sketch or print the graph
(label below).
8.
Store this run.
Part 3 Charging by contact
In Parts 1 and 2, you inserted and removed a charged object in the Faraday pail. What do you expect
would happen if you touched the pail with the charged object?
1.
Continue use of the grounding strap as you did in Part 2. Ground the system and discharge
the charge sensor by pressing and holding the Reset button on the sensor.
2.
To remove any charge from the charge separators, dab each charge separator on a damp
cotton cloth. Insert the charge separators one at a time into the Faraday pail to verify that they
are electrically neutral.
3.
4.
Rub the charge separators together, then set one aside.
Start data collection; be ready to mark events. Insert one of the charge separators into the
middle of the pail without touching the pail (see Figure 2). Wait 4 or 5 seconds, then remove it.
Wait a couple of seconds. Now lightly rub the charge separator across the top edge of the pail
and remove it from the pail. Stop data collection.
5.
Label the marked events. Sketch or print the graph.
6.
Store the run.
Part 4 Charging by induction
In Part 1, you found that touching the grounding plane “removed” excess charge from your finger.
Suppose the pail were grounded with a conducting wire when a charged body was brought close to
it. What effect would this have on the charge of the pail? In this part, you will take a closer look at
the effect of “grounding” in this situation.
1.
Continue use of the grounding strap as you did in Part 2. Ground the system and discharge
the charge sensor by pressing and holding the Reset button on the sensor.
2.
Attach a second grounding wire to the grounding plane, leaving the other end disconnected.
You’ll use this later to ground the pail.
3.
As you did in Part 3, make sure that the charge separators are electrically neutral.
4.
Rub the charge separators together. When you collect data, use the same separator as you did
in Part 3 and set the other one aside.
5.
Start data collection; be ready to mark events. Insert the charge separator into the middle of
the pail (be careful to not touch the side of the pail). Wait 4 or 5 seconds, then remove it. Wait
another couple of seconds. Reinsert the charge separator into the pail, then ground the pail by
briefly touching it with the second grounding wire. Wait 4 or 5 seconds, then remove the charge
separator. Wait a couple of seconds and move the charge separator back into the pail. Wait 4 or 5
seconds, then remove the charge separator and stop data collection. Save your data file.
6.
Label the marked events. Sketch or print the graph.
Y
Separator Added
-h
no
grounded
removed
age
e
Added
Time
EVALUATION OF DATA
It would be helpful for you to view the graph of charge vs. time for only one run at a time. To do
this in Logger Pro, click the vertical axis label, choose More, and select Charge for the run you
wish to view. In LabQuest App, tap the field next to the Filing Cabinet and select the desired run.
Part 2
1.
Make note of the sign of the charge on each charge separator. Compare the magnitude
of the charge on each.
2.
From your answer to Question 1, account for the shape of the graph in terms of the
transfer of charged particles between the charge separators. Account for the features of
the graph when each of the charge separators was in the pail separately and when they
were in the pail together.
Part 3
1.
Account for the shape of the graph in each of these regions in terms of the transfer of
charged particles between the separator and the pail.
2.
Did the charge in the pail return to zero at the end of the experiment? Why or why
not?
Part 4
1.
Account for the shape of the graph in each of these regions in terms of the transfer of
charged particles between the pail and grounding plane and the role of the charge
separator.
2.
Did the net charge in the pail return to zero at the end of the experiment? Why or why
not?
3.
Compare your findings with those who used the other charge separator.
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