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PHYS 432 A: Modern Physics Laboratory

Meeting Time: 
MW 1:30pm - 4:20pm
* *
David Pengra

Syllabus Description:

Physics 432 (Online) - Atomic Physics

Experiments in atomic physics.  Examples are spectroscopy of hydrogen, x-ray spectra, Franck-Hertz effect, Zeeman effect, optical pumping in rubidium and the Hanle effect.


David B. Pengra
Office: Physics/Astronomy Building, Room B256A
Phone: 543-4783

Class Hours (Online)

Section A – Monday & Wednesday, 1:30–4:20
Section B – Tuesday & Thursday, 1:30–4:20

First 30-45 minutes may be used for lecture and general comments.
Each section will be divided into tutorial discussion sections, meeting separately, for about 30 minutes (see below).

Required Reading/Viewing Material

Website (Standard URL links to Canvas page)


There is no required text.  Material will be provided through the course website.

Recommended References:

  • Experiments in Modern Physics, Adrian C. Melissinos (Academic Press, San Diego, CA, 1966 or 2nd ed, 2003).
  • The Art of Experimental Physics, Daryl W. Preston and Eric R. Dietz (John Wiley & Sons, New York, 1991).
  • Atomic Physics, Christopher J. Foot ((Oxford Master Series, 2005).


The 43x series of advanced laboratories are intended to provide a bridge between introductory labs, which are mostly "canned," in the sense that there is a fixed sequence of activities and a fairly rigid analysis to perform, and the kind of "open-ended" research found in real experiments, where you don't really know what will happen or how you should interpret the results. The physics itself is also more complicated than in the intro labs, both in terms of the underlying phenomena and the operation and interpretation of the experimental apparatus. 

In practice, the advanced labs focus much more on data analysis and interpretation.  Basic data reduction is often done with a computer program.  Data sets may be looked at in different ways, i.e., with different types of graphs, with fits to complex curves, and with extra attention paid to calibration steps. In some cases uncertainty calculations must be carried out to complete one's interpretation of the results.  

Interpretation of experimental results is distinct from data analysis.  To interpret the results means to construct a story to explain them within the framework of physical theory, and to note and describe trends, patterns and anomalies in the data.  Interpretation also combines the physics of the phenomena being measured (e.g., nuclear magnetic resonance) with the physics of the apparatus (e.g., a pulsed NMR spectrometer that includes a strong magnet, an RF source, and a pulse generator).  

"Online lab" - what does that even mean?   When you think of a "lab" course, you think of a class in which you gather with your partners around a lab bench to manipulate apparatus.  It is a hands-on activity that gives you the experience of learning to turn knobs, connect wires, and fiddle with oscilloscopes and the like.  This kind of experience is the foundation of all "in-person" lab courses.  Learning of essential skills and a direct encounter with the phenomena are to be found in such courses, and this part of a "lab" course cannot be replaced by purely online tools.

You may wonder, with the loss of such practical hands-on experience, how any online course could call itself a "lab." This loss is real and should not be downplayed.  However, in actual experimental research, hardware manipulation and direct data collection usually forms only a small part of an experimental project.  Indeed, if one conducts experiments at certain large facilities, such as a telescope or particle accelerator, one may never set foot in the lab itself, since the apparatus may be inaccessible (orbiting around the earth or in a desert in Australia), or it may be too specialized and delicate to allow anyone other than trained technicians to operate it (such as a synchrotron beamline at Brookhaven National Laboratory).  Even when you have all of the apparatus to yourself in a single room, most of your time and effort will not be on taking data.  Instead, you spend your days (and sometimes nights) staring at your data, writing code, making graphs, deriving formulas, checking units, staring at your data, talking to your colleagues, reading the literature, staring at your data, and finally writing your paper.

Thus, the "online" course will concentrate on these aspects.  The "experiment operation" part will be presented in video form, and the videos will mainly deal with how the apparatus is assembled and used, and what the experiment looks like when it is running properly.  Data sets will be recorded in a form that most closely matches what you would do yourself were you to be in the lab room; these may be handwritten tables and notes, digital files produced by data collection software, or photographs of oscilloscope traces.  After that, you will carry out the rest of the experimental investigation in the same manner that you would in the normal "in-person" version of the class.

Because of the loss of the experiential part of the lab, more emphasis will be placed on other aspects of experimental work than in the in-person course: you will be asked to read more deeply into how apparatus works, to learn to apply modern computational methods to data analysis, to work with your partners to complete group work, and to write about your experiment - interpret it, critique it, explain it.

Learning Goals

"Learning goals" is a term for the most important skills and understanding you should expect to learn by taking this course.  At the end of this Atomic Physics Laboratory course, you should be able to

  • Explain the concept of "atomic spectra" in terms of how it relates to the structure of atoms and describe different ways that atomic spectra are measured.
  • Derive the energies of transition from measurements of atomic spectra through analysis of different experimental data sets derived from different experimental methods.
  • Relate the energies to the physics of particular atomic systems, for example, the effect of different isotopic mass on the spectrum of hydrogen, the effect of magnetic fields on the spectrum of mercury, and the relationship between an atom's atomic number and the spectrum of x-rays it emits.
  • Carry out complete numerical analysis of experimental data using Python and common computer libraries (numpy, LMFit, matplotlib, etc.)
  • Explain and describe different experimental techniques for the collection of spectra in atomic physics experiments.
  • Explain and describe the operation of apparatus common to such experiments, such as light detectors, multichannel analyzers, the Fabry-Perot interfeometer, and associated test equipment.


The following are rules which you can't violate unless there are special reasons to do so, such as family emergencies, illness, equipment failure, and such.

  • Experimental groups must be no larger than three persons. With four persons or more, there is not enough to do to keep everyone busy.  Tutorial discussion sections will consist of 3-4 experimental groups.
  • Each student must complete both individual assignments and contribute to group work. Students will work together on experiment observation, data reduction and analysis, and they are encouraged to discuss their results with each other (and with other students).  This group work will go into the Group Document (like a lab notebook, but adapted for the online course) for the experiment.  But, each student must independently create their own individual data analysis assignment (a Python notebook) and write a short individual report.
  • Only if and when University restrictions on in-person instruction are lifted may a student or group of students enter the physical lab space in the Physics/Astronomy Building.

Every person is welcome in this course.  Instances of discrimination (e.g., shunning, belittling, bullying, harassment) for any reason (e.g., ethnicity, religion, sexual orientation, gender identity, different-ability, or political beliefs) will incur thorough investigation and possible sanction through University approved processes.  If you believe you have been subject to such discrimination, please contact the instructor directly, or see University Policies for information on how to contact University officials.

Course Structure

The lab will consist of five experiment cycles of two weeks duration each.  Although there are some common themes throughout the experiments in the Atomic Physics Laboratory, each experiment is independent of the others; in other words, a later experiment does not depend directly on an earlier experiment.  However, the experiments will start with those that are "easier" and end with some that are "harder." How easy or hard an experiment will seem depends on your own level of background preparation and concurrent study of the related theory.  The underlying physics draws on electronics, thermal physics, basic quantum mechanics and E&M.  Recommended readings from textbook sections will be posted along with the instructions for each experiment, and you will be expected to draw on that content in your analysis and interpretation.

The experiments will duplicate some foundational discoveries in  atomic physics.  All are associated with Nobel-Prize winning research, and the techniques used in them continue to be used in current research.  This means that each experiment will give only a brief introduction to a deep, rich and complex sub-field; indeed, one could easily spend 10 weeks on any one of the experiments and its related phenomena.

For each experiment you will: meet with your lab partners, watch the videos that show the experiment, read the literature associated with it, study the data sets provided and manipulate them to derive results, perform computational tasks with Python to make graphs, fit curves, and calculate various quantities, collect you work in a group document, and reflect on the experiment and write a brief (2 page) report.  The details follow:

Basic requirements

There is no final exam (or any exam).  Your grade is based on the work submitted and your active participation in the online meetings.

Graded work:

  1. Participation (25%): Meeting participation, question posting/online discussion
  2. Experimental work:
    • Individual analysis tasks (20%)
    • Group document contribution (25%)
  3. Individual reports (30%)

Each of these items is discussed below, along with how they will be graded.

Weekly Tasks

Over each experimental cycle, students should plan to accomplish the following tasks (expected to take 7-9 hours/week), more-or-less in this order:

  1. Read the experiment instructions. Attend the lecture and/or watch video(s) concerning basic theory.  Watch the experimental videos that walk through the experiment structure, operation and data collection. Take notes and think about what you need to learn more about (1-1.5 hrs)
  2. Attend the live Zoom+Slack sessions: (1) the lecture at beginning of class period and (2) the tutorial discussion as scheduled for your group. (0.5 hrs first meeting, 1 hrs second meeting)
    • Meet with group members on Slack to work through the experiment.
    • Post questions/comments/results on Zoom+Slack
  3. Carry out assigned tasks for experiment: typically this involves your individual data analysis plus contribution for group document. (3-5 hours, including additional group meetings)
  4. Write individual report, based on assigned prompt(s). (1 hr)
  5. Before due date: review and sign-off on group document. Upload group document, individual data analysis task and written report.


The core content of this course will be delivered via Panopto or Zoom videos.  There are two basic types: Theory Lectures and Experiment Operation and Data Collection.

Theory Lectures will be about 15-20 minutes in length, one per class meeting (i.e., 2 videos per week).  These are voice-over-slide videos that discuss the important theoretical ideas behind the week's experiments.  They may be given live with a recorded version posted for reference, although some may only be posted. The focus of the "theory" is to help you make sense of the experiments themselves: how the apparatus works, how/where the high-energy particles come from, and how to understand the ways that the experiment illustrates the underlying physics.  Lecture slides will also be available for separate study.

Experiment Operation and Data Collection videos show an experiment in detail: what the apparatus is, how it is assembled, how the electronics are configured and connected together, and any other important physical detail you would need to know in order to operate it. The videos will also show how data are collected, plus other measurements needed for calibration or analysis.  Experiment videos will be broken up into sections of variable length, typically between 5 and 25 minutes each.  For example, one video may give an overview of the apparatus, another may delve into its setup and calibration, and a third may show how data are collected.

Plan to spend some time with these videos.  They are not meant as entertainment but as vehicles for presenting crucial information that would be difficult to transmit in purely written form.  You will often need to extract numerical data from them, as well as derive a diagram of the apparatus.  You are recommended to use the tools under Panopto to set bookmarks, take notes, and generally keep track of the most important sections.

Writing prompts for the individual reports may also refer to topics discussed in these videos, so it is a good idea to have a look at the prompts before watching them.

Zoom Meetings

Each scheduled class period will contain two different Zoom meetings. 

The Lecture Meeting will start promptly at 1:30 pm, Pacific Time, and last 20-40 minutes.  All students in the section are expected to attend because this will be the meeting where information concerning the course as a whole will be discussed, for example, class management and due dates, general questions about the week's activities, or additional lecture material not included in the videos.  The Lecture Meeting will be automatically recorded and saved in the Zoom folder and made accessible to the class.

The Tutorial Meeting(s) will start at a later time (e.g., 2:30 or 3:00) and consist of approximately half the students in the section (5-9 persons), comprising 2 to 3 experiment groups.  It will last 30 minutes.  The second meeting may provide participation credit.   The purpose of the second meeting is for you and your partners to discuss with the instructor, TAs, and other students topics related to the experiment.  These topics may come from prompts provided by the instructors (a question like. "why does the pulse size depend on the PMT voltage?") or from your own contributions to Slack for the experiment.  The Tutorial Meeting will be recorded for grade-keeping purposes only; it will not be posted for access by the class.

Office Hours

In addition to the scheduled meetings above, the instructor and TAs will be available on Zoom for "office hours" at other times during the week.  TAs will arrange their own schedule for office hours.  For office hours with the instructor, please send a Direct Message (DM) through Slack.

Participation Credit

To earn participation credit YOU MUST PARTICIPATE.  There are various ways to earn participation credit:

  • Attend the tutorial meeting and speak up in audio discussion and/or contribute to discussion via "Chat" posts. Your meeting attendance will be recorded by Zoom, as well as any posts you make in the Zoom chat.  As noted, your audio comments will also be recorded for this grading purpose. If you are registered as present but do not participate via post or discussion, you will receive 50% credit for that day.  You do not receive credit for attendance in the Lecture Meeting.
  • Post on Slack during the Tutorial Meeting time.  You may remain anonymous to all other students through a Slack DM (direct message), or anonymous to students outside your group if you post in your group's private channel.
  • Post on Slack during times outside of the Tutorial Meeting within 24 hours of the meeting time. 
  • Post answers to Checkpoints on Slack within 24 hours of the Tutorial Meeting.  A Checkpoint is a required task of the experiment that you complete well before the due date.  (It is not "extra work.")  The purpose of a Checkpoint is to keep you and your group on track to complete the assignment on time.  Checkpoints may be data analysis tasks, answers to conceptual questions, calculations, or brief research topics.  They will be posted on Slack in the public channel for the experiment.

Posted comments must be germane to the experiment, for example, "I'm here and have no questions." would not count towards participation.

To summarize: you earn participation credit on a given day by (A) speaking up during Tutorial Meeting, (B) Posting on Zoom Chat or Slack during Tutorial Meetings, or (C) Posting on Slack within one day of the Tutorial Meeting.

Working Groups

Research is a collaborative process.  Most scientific work is done in teams, some quite large.  Even if you are a solo theorist, you need to talk to others to refine your ideas, brainstorm and challenge assumptions.  Thus, learning how to work in a group is essential.  In experimental research, projects are broken down into specific tasks to be accomplished by subject experts (e.g., coding, hardware, sample preparation) and those who may be learning the field (e.g., grad students).

You will be expected to form a group of 2-3 persons in your section.  Group membership will be assigned by the instructor, and initially it will be based on your answers to a short survey (See Main Page) that will also ask about your personal preferences.  For example, are you a strong computer coder or are you just beginning to learn?  Do you like to plan your tasks in detail or just start fiddling with the data?  Which would you rather do: experiments or theory?  Also, do you know someone in the class that you have worked well with in the past (or conversely, someone you may have had a bad experience with)?  The goal of the survey is to get information to form groups whose members can complement each other, but who also have a good chance of forming productive working relationships.

Group members are not  bound to the same group for the duration of the course, but if possible, those groups working well together will be preserved.

What Your Group Should Do

At minimum, your group has two main tasks:

  1. Decide which members are primarily responsible for which tasks to complete the group document.
  2. Decide when and how to meet/communicate, outside of the scheduled class meetings, to accomplish and assess your group's progress.  You are strongly recommended to use the Slack page to coordinate with group members and TAs/instructor.

For each experiment there will be a set of tasks assigned to the group.  For example, to create a diagram of the apparatus, to perform basic data reduction, to carry out a particular calculation.  Your group should decide who is most responsible for a particular task, and also decide on how the other members will monitor progress, offer advice, ask questions, etc.

Members should also plan to rotate tasks from experiment to experiment.  In other words, do not always have the same person draw the apparatus diagram, or carry out basic data reduction.

The other main purpose of the group is to work together to accomplish the data analysis tasks that should be completed by every member.  Such tasks are important enough that these will be assigned to all students.  However, it is expected that your group may work together and help each other solve these problems.

Group Documents

The "group document" is the primary product of the working group.  It should be created with a collaboration platform such as Google Docs.  The group document should be made accessible to the TAs and instructor so that they can view and comment on it during the course of the experiment. The easiest way to do this is to copy the Group Document template into a fresh document on Google Docs or Office 365 and link it to your Slack channel.

What Goes in the Group Document?

To complete the group document, use the template for the particular lab (posted on the experiment page).  The template lists the tasks to be completed and some information on how to accomplish them.  The template also indicates spaces for other information, such as the group members and contact info, who is assigned primary responsibility for which part, and reminders for the other members to review and sign-off on each section.

More information on how to set up the group documents and criteria for them are in Getting Started with Group Documents.

Individual Data Analysis Assignments

Some data analysis tasks will be assigned to all students. You may think of these like "homework" for a lecture class, but distinct from the writing focus of the Individual Reports.

There are two reasons for making such assignments not part of the group. 

First, such assignments usually concern core concepts in the experiment, such as creating a calibration, or finding an important quantity with a line fit.  Everyone in the class should know how to do these things, not just the one person who might be assigned to that task in the group.

Second, among the learning goals of this course involve building skills with computation as applied to experimental physics.  Data analysis tasks will be carried out with Python on Jupyter Notebooks.  This is part of an overall department effort to teach computation within the physics major.  The use of Python is based upon current trends in physics research, data science generally, and the growth and maturation of collaborative tools associated with Python.  See Python and Jupyter Notebooks for more information.

Individual Reports

Each student must also write and submit their own individual report, as a PDF uploaded to a Canvas assignment.  The structure and content of the report will be described in the assignment, and will vary as the course proceeds, but there are a few common aspects:

  • It must conform to strict formatting rules and length limits.  Typically,  a report must be between 1 and 4 pages (2 is the intended length), be typed, use 11 or 12 point font and 1 inch margins.
  • It must be written well, with complete, grammatically correct sentences and structured paragraphs.
  • It must address certain questions or topics in a certain order.  The writing prompt for the assignment will be posted on the experiment page.


The experiments are

  1. Hydrogen-deuterium spectrum
  2. X-ray fluorescence spectra
  3. The Franck-Hertz effect
  4. The Zeeman effect in mercury
  5. Laser Spectroscopy and the Lamb shift in hydrogen

Links to information about these experiments are posted on the main course page.


Overall grade portions are 25% participation, 45% experiment, 30% individual report.  These are further broken down as described below.


Zoom+Slack meetings & postings

Credit for participation will be assessed for each scheduled day. The participation credit will also follow a trinary scheme: A = Participation, as defined above;  C = Present in tutorial meeting only;  F = No participation. 

Participation will determine the participation grade (25% of total).

The student course evaluation will count for one participation day, as part of the total (not extra credit).


Group Document

Group document grading will reflect "real-world" assessments: the kinds of assessments that are typical in work environments and active research.  Notebook assessments will be listed as letter grades A, B, C, D, F which correspond to numerical grades 4, 3, 2, 1, 0, and are based on the typical workplace assessments outstanding, exceeds expectations, satisfactory, below satisfactory, nothing to assess

The Group Document grade will be broken into an overall scoring and an individual scoring.  Because different parts of the group document will be the primary responsibility of different members, the grade for a particular portion will be awarded to the group member with responsibility for it.  Because all members should work together to produce the final document, review, and sign-off on the other parts, the document as a whole will be assigned an overall grade, approximately equal to a weighted average of the individual parts.  (The weighting will depend on the relative importance of different sections, and vary from experiment to experiment).

The group document will account for 5/9 of the experiment grade (i.e., 25% of total).  Within a group document, the individual portion will be worth 3/5 and the overall portion will be worth 2/5.  The individual student's grade for the notebook will be calculated according to the formula

LaTeX: \text{Grade} = \frac{(\text{Indvidual grade})\times15\,+\,(\text{Overall grade})\times10}{25}

rounded up to the nearest +/- letter grade.  For example, if the individual grade is A (4.0) and the overall grade is B- (2.7) then the student's grade would be 3.48 which rounds up to 3.7, or A-.

Individual Data Analysis

Individual data analysis assignments will be done in Jupyter notebooks, converted to PDF, and uploaded to canvas for grading.  They will be graded according to the letter scale used for the Group document (A-F) and account for 4/9 of the total experiment grade (20% total).

Individual Report

The Individual Report will count for 30% of the total.  It will be subject to grading as follows:

If it is turned in by the due date (or a mutually agreed upon extension of the due date) it will be graded on a 3 level scale, corresponding to typical decisions made by scientific journals: accepted (A), accepted with revisions (AwR), and rejected (R).  These will correspond to letter/numeric grades of A/4.0, B/3.0, and F/0.0.  Reports that earn AwR or R may be resubmitted once. Exceptions to the submission process may occur if there is not enough time to grade, return, and resubmit, such as at the end of the term. A report that falls below a grade of AwR on its final submission will be graded B-, ..., R.  Reports that are originally graded R (0) but not resubmitted will retain the grade of 0.

If it is turned in past the due date, even if submitted within the grace period, it will be graded once on an A, AwR, B-, ..., R scale.  (Note there will be no A-, B+ grades, to make the scale consistent with the preferred submission-cycle scale)

To summarize:

Contribution Scale Percent of total
Participation A, C, F 25%
Group document A-F 25%
Individual Data Analysis A-F 20%
Individual Report A, AwR, R / A-F 30%

Due dates & Extensions

In order to keep things simple but also reduce stress, due dates are structured in the following way:

  1. There is a single due date for all documents (Group Document, Data Analysis task, Individual Report) for an experiment cycle: midnight (strictly 11:59pm) of the day a new cycle starts.
  2. There is an automatic grace period of 48 hours following the due date.  Think of this as an automatic extension, should you need to talk to the TA or instructor.  You do not need to ask for this extension.  However, Individual Reports turned in during the grace period or later will be graded only once.
  3. Extensions beyond the grace period will be granted, but they must be requested before the end of the grace period.  A new due date will be assigned to work granted an extension.
  4. Late work that has not been granted an extension according to the above will not be graded, except by appeal to the instructor.  It will be marked as F following the grace period.

For example, if you are in section B (T, Th), your first set of assignments (Experiment 1) will be due Tuesday, 13 April, at midnight.  You may delay without penalty or special request submitting one or more parts until Thursday, 15 April.  If you need an extension on any part, it will be granted (without penalty) as long as that request is made before the end of Thursday, 15 April.  But, if you do not turn anything in by the end of Thursday, 15 April, your grade will be assigned a zero (F) for the missing work.  You may appeal to the instructor if you have extenuating circumstances.

Grade Calculation

The final grade will be calculated according to the formula

Grade =
Percent score
× 4.2

Thus, to earn a 4.0, you need about 95%.

Writing ("W") Option

A writing "W" credit will be awarded to any student who earns at least 4 "Accept" grades on their Individual Reports.

University Policies

A number of University of Washington policies pertain to this course, including those concerning religious observances.  See University Policies.

Catalog Description: 
Experiments in atomic physics, e.g., x-ray fluorescence, hydrogen-deuterium spectrum, Zeeman effect, optical pumping, hydrogen fine structure. Prerequisite: PHYS 225 and PHYS 334. Offered: Sp.
GE Requirements: 
Natural Sciences (NSc)
Section Type: 
Last updated: 
April 16, 2021 - 9:51pm