PHYSICS 174
Laboratory Manual
Student Name:__________________
Section Number: ________
Department of Physics
University of Maryland
College Park, Maryland, 20742-4111
Ninth edition – December 2005
PHYSICS 174 - TABLE OF CONTENTS
0. Getting started in Physics 174
1. Introduction to Excel
2. Measurement Error and Uncertainty
3. Measurements, Averages and Standard Deviations
4. Straight Line Fits Using 2 and Excel
5. Propagation of Errors
5*. Using 2 to test a Theory
6. Review of Spreadsheets and Errors
7. Practical Test on Spreadsheets and Errors
8. Resistors and Multimeters
9. Current and Voltage
10. The Digital Oscilloscope and the Function Generator
11. The Oscilloscope and AC Signals
12. Reflection of Voltage Pulses
13. Review of Circuits
14. Practical Exam on Circuits and Error Analysis
Appendix A: Using Vernier Calipers
Appendix B: The Digital Oscilloscope and The Function Generator
Appendix C: Multimeter Specifications and Uncertainties
Published and Printed by The Department of Physics, University of Maryland, College Park,
Maryland 20742-4111 9th printing, Spring 2006, 8th printing Fall 2004,7th printing Summer
2003, 6th printing July, 2000, S.C. Eno and N.J. Hadley, Second-5th printings, F.C.Wellstood,
J.R. Anderson, S.C.Eno, N.J.Hadley
First Printing January 1998, F.C. Wellstood and J.A. Goodman
Corrections and comments may be sent to well@squid.umd.edu
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Getting Started in Physics 174
What You Need to bring to the Lab every time
1. This lab manual.
How to Get a Good Grade in this Lab
1. Don't miss classes and don't be late for class. During the first ten minutes, your
instructor will discuss the experiment, give helpful suggestions, and tell you about any
changes in procedure. If you're more than 10 minutes late, you may not be let in to the lab.
2. Learn how to use the spreadsheet program.
3. If you are working on the computer, remember to save your work at least once every 15
minutes.
4. Whether or not you have finished all of a lab, never leave the class-room until you have
submitted a copy of your spreadsheet to your instructor via WebCT. You can always
turn in a revised version later if there is something you need to finish, but that does not
change your obligation to turn in a copy before leaving. Failure to submit a lab before
leaving is probably the number one reason why students have to completely redo labs.
5. Make a disk copy of your spreadsheet before leaving the lab and make sure that you have
your disk before you leave the lab.
5. Read the course textbook about error analysis.
6. Do the Homework and turn it in on time.
7. If you have questions, ask your instructor or the TA. You may find this hard to believe,
but its part of our job to explain things to you and we get paid good money to do so. We
expect you to have questions and we enjoy explaining how things work. If your question
arises after class, don't be shy about sending an e-mail to your instructor or TA.
8. Fill in the following blanks so that you can reach your instructor and TA when you need to.
Instructor's name:___________________ phone #__________ e-mail ________________
TA's name:________________________ phone #__________ e-mail ________________
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Philosophy of the course
Physics 174 was first taught in the Spring semester of 1997 by Professor Jordan
Goodman. The course was started after the Department of Physics examined the physics majors
curriculum and discovered some problems in the laboratory program. What we found was that
students were not mastering the basic skills that they needed for working in a laboratory. Problem
areas included use of computers (spreadsheets, fitting, plotting), use of measurement tools
(vernier calipers, meters, oscilloscopes), and understanding error analysis.
Physics 174 is designed to introduce you to the basic skills and tools you will need for
working in the Physics Department's laboratories. Over the course of the semester, you will have
the opportunity to use some instruments and do some simple experiments with them. Specific
goals will be outlined for each section of the course. At the conclusion of each section you will
be required to demonstrate that you have mastered the key skills. For example, you will have to
demonstrate that you can use an oscilloscope and get it to trigger on an unknown signal. If you
do not pass this demonstration you will be required to practice some more and then demonstrate
that you can do it. The essence of this course is to train you with the tools you need and to make
sure that you learn how to use them. To help you, at the beginning of each lab and at intervals
during the lab, your instructor will get the class together and discuss what is going on. You will
have plenty of chances to take data, as in a traditional physics lab, but you will not perform and
write up complete physics experiments; that's reserved for the more advanced labs. Occasionally
you will work in small groups to collect data, but normally you will work by yourself and be
tested individually.
Analytical Tools for the Lab
Physics 174 begins by introducing you to two common analytical tools used in
experimental research: spreadsheets and error analysis. By using a computer spreadsheet, you
will be able to save yourself a lot of time and trouble analyzing and plotting data. If you are
already familiar with the spreadsheet program Excel, then you are way ahead and we might even
ask you to help out some of your classmates. If you don't know how to use Excel, don't worry
because we'll go over it in the first lab.
Why Study Error Analysis?
As you work through the labs, you may find yourself wondering: what is the point of
error analysis anyway? Error analysis plays a key role in physics because physics is an
experimental science. What this means is that theories are judged by how well they explain the
world we live in, and those theories don't agree with experiments are thrown aside. In many
experiments, the idea is to determine whether a given theoretical result or law of physics is
actually obeyed in the real world. One soon finds that this is not so easy to do. One reason is
that a measurement of a physical quantity, such as current or voltage, can only be made to within
a certain accuracy and a certain precision. Because of this, it turns out that one cannot prove with
mathematical rigor by doing experiments that a physical law is true. The best you can do is show
that your measurements agree with theory to within your experimental uncertainties. Thus, it is
essential to learn about measurement errors and uncertainties before you can decide whether a
theoretical result actually agrees with an experiment.
Ultimately, what you will get from understanding error analysis is the ability to design
proper experiments of you own and evaluate the work of other scientists. However, this will take
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several semesters of labs. In Physics 174, we aren't going to try to teach you everything there is to
know about error analysis. In fact, while the subject is quite fascinating, many aspects are too
complicated or difficult for an introductory lab course. Instead, what we want to do is teach you
enough so that, by the end of the lab course, you can use error analysis in some simple cases and
understand what it means to “prove” something experimentally. Without question, most students
have a difficult time "getting it", so don't be shy about letting your instructor know if something
isn't clear or doesn't make sense to you.
Course Textbooks
The required textbook for the course is "A Practical Guide to Data Analysis for Physical
Science Students", by Louis Lyons. We can also recommend "An Introduction to Error Analysis"
(second edition) by Taylor. Lyons is shorter, but Taylor is more user-friendly. Both books
provide a good introduction to error analysis and will be useful for later labs as well. For help
with spreadsheets, the recommended text is " Microsoft EXCEL Version 2000: Plain & Simple"
by Microsoft Press.
About the Equipment
The equipment used in the Physics 174 lab is fairly simple and durable. However, treat
all the equipment with care. Not only will the students who follow you be grateful, but you will
get better data. If something is broken or you experience a problem, immediately inform your
instructor or one of the lab technicians. In most cases, it should be possible to fix things or
provide a replacement with very little delay.
Safety First
The equipment you will be using in Physics 174 is quite safe. However, always think
about the potential dangers when using any piece of equipment; even a small mouse has sharp
teeth and can give you a painful bite. If you have doubts about how something should be used, or
if you think something might be dangerous, let your instructors know immediately.
Changes to the Seventh Edition of the Manual
The main changes to this edition of the manual are the correction of small typographical
errors and the addition of Experiment 5* on using 2 to test a theory. Instructors who feel that
students need more exposure to 2 should choose Experiment 5*, while Experiment 5 should be
chosen if it is felt that additional work is needed on propagation of errors. If both 5 and 5* are
assigned, then the best choice is to drop Experiment 12 so that the course to fits into a semester.
Acknowledgments
Special thanks go to the many students of Physics 174 who have helped us to create this
course and turn it into a fun and useful part of the Physics program at Maryland. We'd like to
especially thank William Parsons, who while taking the course also took the time to go through
the second edition with a fine editorial eye, correcting many errors and suggesting useful changes
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to help future students. We also acknowledge many valuable suggestions from Teaching
Assistants Phil Johnson and Paul Branoff, who contributed greatly to the success of the course.
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