Lab Manual

169 Pages·2002·1.971 MB·English

by  Crowell B., Roundy V.

Lab Manual
Benjamin Crowell and Virginia Roundy
Fullerton College
www.lightandmatter.com
Copyright(c)1999-2002byB.CrowellandV.Roundy. ThislabmanualissubjecttotheOpenPublication
License on page 166. If you do not agree to the license, then you do not have permission to copy the
manual. The lab manual is available for downloading from www.lightandmatter.com, and a copy of the
Open Publication License is also available at opencontent.org.
2
Contents
1 Kinematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Interactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3 Free Fall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4 Newton’s Second Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5 Air Friction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6 Acceleration In Two Dimensions . . . . . . . . . . . . . . . . . . . . . . . . 22
7 Vector Addition of Forces. . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8 Vector Addition of Forces. . . . . . . . . . . . . . . . . . . . . . . . . . . 26
9 Conservation Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
10 Conservation of Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
11 Conservation of Momentum . . . . . . . . . . . . . . . . . . . . . . . . . . 36
12 Conservation of Momentum in Two Dimensions. . . . . . . . . . . . . . . . . . . 38
13 Torque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
14 The Moment of Inertia. . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
15 Absolute Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
16 The Pendulum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
17 Resonance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
18 Resonance (short version). . . . . . . . . . . . . . . . . . . . . . . . . . . 56
19 Standing Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
20 Resonances of Sound . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
21 Static Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
22 The Oscilloscope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
23 The Speed of Sound. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
24 Electrical Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
25 Kirchoff’s Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
26 Electric Fields and Voltages . . . . . . . . . . . . . . . . . . . . . . . . . . 80
27 The Dipole Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
28 Magnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
29 Relativity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
30 The Charge to Mass Ratio of the Electron. . . . . . . . . . . . . . . . . . . . . 94
31 RC Circuits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
32 Energy in Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
33 LRC Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
34 Faraday’s Law. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
35 Electromagnetism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
36 Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
37 Refraction and Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
38 Geometric Optics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
39 Two-Source Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
40 Wave Optics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
41 Polarization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
42 The Photoelectric Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
43 Electron Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
44 The Hydrogen Atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
Appendix 1: Format of Lab Writeups . . . . . . . . . . . . . . . . . . . . . . 148
Appendix 2: Basic Error Analysis. . . . . . . . . . . . . . . . . . . . . . . . 150
Appendix 3: Propagation of Errors . . . . . . . . . . . . . . . . . . . . . . . 154
Appendix 4: Graphing. . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
Contents 3
Appendix 5: Finding Power Laws from Data. . . . . . . . . . . . . . . . . . . . 158
Appendix 6: Using the Photogate. . . . . . . . . . . . . . . . . . . . . . . . 160
Appendix 7: Using a Multimeter . . . . . . . . . . . . . . . . . . . . . . . . 162
Appendix 8: High Voltage Safety Checklist . . . . . . . . . . . . . . . . . . . . 164
Appendix 9: Laser Safety Checklist . . . . . . . . . . . . . . . . . . . . . . . 166
Appendix 10: The Open Publication License. . . . . . . . . . . . . . . . . . . . 168
4 Contents
Contents 5
1 Kinematics
Apparatus Setup
computer ................................1/group Set the cart on the track without the fan. Prop
track ....................................1/group the motion detector (sonar gun) at one end of the
dynamics cart ...........................1/group tracksothatitisaimedslightlyupward. Thisangle
fan ......................................1/group is critical — measure 86◦above horizontal with the
AA batteries .............................4/group protractor, and tape it to the backrest.
aluminum slugs ..........................2/group
With the computer turned off, plug the motion de-
motion detector ..........................1/group
tector into the PORT2 plug on the interface box.
protractor ...............................1/group
Startupthecomputer. Forcompactness,I’lluseno-
tationlikethistodescribethecomputercommands:
Start>Programs>Vernier Software>Logger Pro
Goal
Thisisthecommandtostartthecomputersoftware
Learn how to relate the motion of an object to its
running. “Start” means to click on the start menu
position-versus-time graph.
at the bottom left corner of the screen, “Programs”
means to select that from the menu, and so on.
Introduction Make sure that the interface box is plugged into
COM1(thefirstCOMport)atthebackofthecom-
Analyzing motion is the most fundamental thing we
puter, not COM2. If the computer presents you
doinphysics. Themostversatilewayofrepresenting
with a dialog box saying “Set Up Interface,” choose
motioniswithagraphthathastheobject’sposition
COM1.
on the upright axis and time on the horizontal axis.
It takes some practice to be able to sketch and in- Once the program is running, do File>Open, then
terpretthesegraphs,butonceyougetusedtothem, go into Probes and Sensors and then into Motion
they become very intuitive. Detector. At this point, you may get the following
error message, which you can ignore: “This file can-
not run properly with this hardware interface.”
Apparatus
You’ll get three graphs on the screen, but you only
want one, the x−t graph. Click on the x−t graph,
The object whose motion you’ll study is a cart that
and then do View>Graph Layout>One Pane, and
rolls on a track. You can either push the cart by
the other two graphs will go away.
hand,startitmovingwithashove,orclampafanon
top of it to make it speed up or slow down steadily. If you now click the button to tell it to collect data,
Tomeasurethecart’smotion,you’llusealittlesonar the motion detector should start clicking rapidly,
gun that sends out clicks. When it hears the echo and it you move the cart back and forth you should
from the cart, it figures out how far away the cart see a graph of its motion. Make sure it is able to
wasbasedonthetimedelayandtheknownspeedof sense the cart’s motion correctly for distances from
sound. The sonar gun is connected to a computer, 50 cm to the full length of the track. If it doesn’t
which produces a position-versus-time graph. work when the cart is at the far end of the track,
play with the angle of motion detector a little.
Observations
InpartsAthroughE,youdon’tneedtotakedetailed
numericaldata—justsketchthegraphsinyourlab
notebook. Allofyourgraphswillhavegarbagedata
atthebeginningandtheend,andyouneedtomake
sure you understand what’s what.
6 Lab1 Kinematics
A Fastandslowmotion F Changingthedirectionofmotion
Moving the cart by hand, make a graph for slow Change the fan back to full strength.
motion and another for fast motion. Make sure the
Now suppose instead of releasing the cart from rest
motionissteady,anddon’tgetconfusedbytheparts
close to the motion detector, you started it moving
of the graph that come before and after your period
with a push toward the motion sensor, from the far
ofsteadypushing. Sketchthegraphsandmakesure
end of the track. It will of course slow down and
you understand them.
eventually come back. Discuss with your partners
Any time you want a close-up view of part of a what the position-time graph would look like. Now
graph, do View>Graph Options>Axis Options to try it.
select ranges of time and position values that you
G Rateofchangingspeed
want. (Notethatifyoutakedifferentdatalater,you
may need to fiddle with this again because you’ll be The goal of this part of the lab is to determine
zoomed in on the wrong part of the new graph.) whetherthespeedofthecartinpartFwaschanging
at a constant rate, i.e., by the same amount every
B Motionintwodifferentdirections
second.
Now try comparing the graphs you get for the two
Zoominontherelevantpartofyourgraphfrompart
different directions of motion. Again, record what
F, and print out a big copy. If the printer in room
they look like and figure out what you’re seeing.
418 is working, you can do this simply by choosing
C Reproducingagraph File>Print in Logger Pro.
Now see if you can produce a graph that looks like Ifthatprinterisn’tworking,here’swhatyouneedto
this: do instead. Do File>Export Data, and select “.txt”
for the type of the file. Use a text editor such as
WordPad to delete the header from the file. Save it
x
in your FC student directory, and also on a floppy
disk if you intend to work on it at home. Get into
OpenOffice or Excel, and open the file. Appendix 4
describes how to use OpenOffice. Whatever method
youuse,makesurethewholegroupwillendupwith
copies.
t
If you’re using Excel or OpenOffice to make your
graph, you can make the grid overlaid on the graph
D Acceleratingawayfromthesensor haveaveryshortspacingbothhorizontallyandver-
tically, to give the best possible accuracy when you
Suppose the fan is mounted on the cart as shown
measuretheslopesofthetangentlines. Ifyou’reus-
in the figure, so that if the cart is released from a
ingLoggerPro,theredoesn’tseemtobeanywayto
position close to the motion detector, it will begin
control the grid’s spacing, so the simplest thing to
moving away from it. Predict what you think the
do is simply to use a ruler to measure vertical and
cart’s position-time graph will look like, and show
horizontal distances, and determine the slopes from
your prediction to your instructor before getting a
these; although the resulting slopes won’t be in any
fan.
standard units, that won’t affect your conclusion.
Beforeputtingthebatteriesinthefan,makesurethe
fan’sswitchisoff(totheright). Putthebatteriesin
and clamp the fan on the cart. Prelab
Set up the situation described above, and compare Thepointoftheprelabquestionsistomakesureyou
the results with what you predicted. understand what you’re doing, why you’re doing it,
and how to avoid some common mistakes. If you
E SloworRapidAcceleration
don’t know the answers, make sure to come to Al’s
The aluminum slugs can be used to replace two of Placebeforelabandgethelp! Otherwiseyou’rejust
the batteries so that the fan will exert about half as setting yourself up for failure in lab.
much force. Discuss with your partners what you
P1 Makeapredictionofthefourgraphsyou’llob-
think will happen if you repeat your previous run
tain in parts A and B.
with a weakened fan. Now try it.
7
Self-Check
Do the analysis in lab.
Analysis
Atone-secondintervals,drawnicelongtangentlines
onthecurvefrompartGanddeterminetheirslope.
Some slopes will be negative, and some positive.
Summarize this series of changing speeds in a table.
Didthevelocityincreasebyaboutthesameamount
with every second?
8 Lab1 Kinematics
9
2 Interactions
Apparatus ball being pushed outlines two relationships involv-
ing four objects:
single neodymium magnet ................1/group
triple neodymium magnet ................1/group The earth is the rock's natural place.
compass earth rock
triple-arm balance ........................2/group
clampand50-cmverticalrodforholdingbalanceup
string The hand gives motion to the ball.
hand ball
tape
scissors
According to Aristotle, there are asymmetries in-
heavy-duty spring scales
volved in both situations.
rubber stoppers
(1)Theearth’sroleisnotinterchangeablewiththat
of the rock. The earth functions only as a place
where the rock tends to go, while the rock is an
Goal
object that moves from one place to another.
Form hypotheses about interactions and test them. (2) The hand’s role is not analogous to the ball’s.
The hand is capable of motion all by itself, but the
ballcan’tmovewithoutreceivingtheabilitytomove
Introduction
from the hand.
Why does a rock fall if you drop it? The ancient If we do an experiment that shows these types of
GreekphilosopherAristotletheorizedthatitwasbe- asymmetries, then Aristotle’s theory is supported.
causetherockwastryingtogettoitsnaturalplace, If we find a more symmetric situation, then there’s
incontactwiththeearth. Whydoesaballrollifyou something wrong with Aristotle’s theory.
push it? Aristotle would say that only living things
havetheabilitytomoveoftheirownvolition,sothe
Observations
ball can only move if you give motion to it. Aristo-
tle’sexplanationswereacceptedbyArabsandEuro-
The following important rules serve to keep facts
peans for two thousand years, but beginning in the
separate from opinions and reduce the chances of
Renaissance, his ideas began to be modified drasti-
getting a garbled copy of the data:
cally. Today,Aristotelianphysicsisdiscussedmainly
by physics teachers, who often find that their stu- (1)Takeyourrawdatainpen,directlyintoyourlab
dents intuitively believe the Aristotelian world-view notebook. Thisiswhatrealscientistsdo. Thepoint
and strongly resist the completely different version is to make sure that what you’re writing down is
of physics that is now considered correct. It is not a first-hand record, without mistakes introduced by
uncommon for a student to begin a physics exam recopying it. (If you don’t have your two lab note-
and then pause to ask the instructor, “Do you want books yet, staple today’s raw data into your note-
ustoanswerthesequestionsthewayyoutolduswas book when you get it.)
true,orthewaywereallythinkitworks?” Theidea
(2) Everybody should record their own copy of the
ofthislabistomakeobservationsofobjects,mostly
raw data. Do not depend on a “group secretary.”
magnets, pushing and pulling on each other, and to
figure out some of the corrections that need to be (3) If you do calculations during lab, keep them on
made to Aristotelian physics. a separate page or draw a line down the page and
keep calculations on one side of the line and raw
Some people might say that it’s just a matter of
data on the other. This is to distinguish facts from
definitions or semantics whether Aristotle is correct
inferences.
or not. Is Aristotle’s theory even testable? One
testable feature of the theory is its asymmetry. The Because this is the first meeting of the lab class,
Aristotelian description of the rock falling and the there is no prelab writeup due at the beginning of
the class. Instead, you will discuss your results with
10 Lab2 Interactions