oscillations with semi-coordinated lab

basketontarioElectronics - Devices

Nov 2, 2013 (3 years and 9 months ago)

91 views

First semester sophomore physics:
The advantages of waves &
oscillations with semi
-
coordinated lab

Walter F.
Smith

Physics
Dept. Haverford
College

Haverford PA


Conference on Laboratory Instruction
Beyond the First Year of College

Philadelphia, July 25, 2012


A tension in education:

depth vs. breadth



Sophomore physics:

varies quite widely



One common approach:

Modern Physics





Relativity





Quantum mechanics





Nuclear physics





Particle physics





Statistical mechanics

Approach to sophomore physics at Haverford College:


Rigorous quantum mechanics in lecture and lab


Lecture:

Advantages:


Quantum mechanics is very exciting to students!


Central to many hot areas of research (e.g. q. computing, q. info)


Philosophically challenging (e.g. entanglement, locality, …)


Required for many of our most impressive results (transistors,



solar power) and most important challenges




Gives students a real insight into the physics major



before they declare





Disadvantages:


Only 1
-
2 weeks on relativity in first 2y (during 1
st
-
year
e&m
)


There are many exciting areas of physics that don’t involve
q.m
.

http://www.latimes.com/news/science/la
-
sci
-
quantum
-
entanglement
-
20120707,0,802675.story

Our experience at Haverford:


Originally, students began study of quantum right after two
semesters of intro


Most students struggled, achieved poor understanding



New system:


Semester 1: Waves and Oscillations


Semester 2: Quantum Mechanics



Works very well!


Increased number of majors

(~12 per year, with student


body of 1200)


Excellent, supportive


atmosphere among majors

Advantages of Waves & Oscillations in the sophomore year:


Important in most areas of physics


Electricity & magnetism


Anything involving quantum


Acoustics


Plasmas


Nanoscience


Provides exactly the mathematical ideas and techniques
needed for quantum (and many other areas), in a less
intimidating classical context


Differential equations


Complex exponentials


Matrix math


Hilbert space and orthogonal function analysis (e.g.
Fourier analysis)


Eigenvalue

equations


Bra
-
ket

notation


Advantages of sophomore Waves & Oscillations (
ctd
.):



Most of material is new to students (e.g. coupled
oscillators), but connected to things they’ve studied
before & understand


Gives students a feeling of the challenge they will see in
upper
-
level courses

Text:

Connections to current research:


Whale calls:

Total internal reflection fluorescence microscopy:

Prof. Christopher Clark, Cornell Univ.

A.
Gunnarson

et al.,
Nano

Letters
8
, 183
-
188 (2008).

Connections to “everyday” life:


Magnetic
Resonance
Imaging

Quartz crystal

f
rom a watch

Dr. Erhard
Schreck

Web support with custom
-
developed

a
pplets & links to web resources

Custom
-
developed

c
oupled pendulum

a
nd Hilbert space

applet

Link to

Physical Review Focus
summary of

Physical Review Letters

paper on bat sonar

Prof. Rolf
Müller
, Shandong Univ.

Bra
-
ket

notation for coupled oscillators


Refreshing writing style


Humor when appropriate



Check it out Thursday in Poster Session I

Semi
-
coordinated lab:

Goals of our first
-
semester sophomore lab:


Transition to more independent lab work:


Second semester sophomore lab


Advanced lab (junior / senior)


Research


Provide common background of experimental expertise:


Simple electronics (input & output impedance, scope operation,



op amps)


Better understanding of optics


Coherent presentation of results


Three oral reports


Two full
-
length written reports


Reinforcing data analysis: Uncertainty analysis, curve fitting

Another tension in education:

creativity/exploration vs.


learning the ropes

Another tension:


Challenging your students to stretch themselves



vs. Discouraging them








Oral reports:


Presentations based on data graphs, tables,


etc. (not PowerPoint)


Given to an instructor


Presentations in pairs


Typically about 30 minutes

Overview of the lab:


Another tension:

Reinforcing understanding vs. introducing new material


At a variety of intervals





Connected to old material


(reading, class, problem sets,


lab, exams, other courses,


research)


Using different parts of the brain




New context






Half
-
credit, usually taken in the same semester as the
lecture component


First five weeks are single
-
week labs, done in unison by pairs,
coordinated with lecture.


Week 1: Input and output impedance for DC circuits


Essential concepts for all electronics

Week 2: High
-

& low
-
pass filters


Connects to complex notation for AC circuits in
lecture

Week 3: Resonant circuits


Connects to ideas in lecture

Week 4: Diodes


Crystal radio; synthesizing concepts

Week 5: Op amps


What is an amplifier? What is gain?


Feedback


The connection between a schematic & physical
circuit


Debugging


Last 9 weeks are a series of two week labs (plus a week off!).


Done in rotation by pairs of students.


Not coordinated with lecture.


Why only semi
-
coordinated?


Equipment costs


Allowing students to encounter some things in lab first


Variability in timing between the lecture & lab is OK


Less sense of competition for fastest completion


Students who’ve done the lab previously help the current
students, building camaraderie.





Dispersion relation of water waves


The beginnings of how to be


really clean


Challenging non
-
linear curve fitting


Dispersion relations can be


non linear


Torsional

oscillator (
TeachSpin
) & coupled oscillators


Connects to key concepts from lecture


Further practice with scopes, function generators


Computer acquisition of voltages


Reinforces concepts of Faraday’s Law, and creating
B

with current

wiki.brown.edu/confluence/display/


PhysicsLabs
/Experiment+120


Diffraction as a Fourier transform and spatial filtering


Connection to lecture


Deeper understanding of optics


Practice thinking in reciprocal space


Simple optical design exercise: beam expander


Optical setups using research
-
grade components


Aspects of laser safety











www.doitpoms.ac.uk/tlplib/DD1
-
6/image.php



Ultrasound imaging


Applications of wave ideas to a new context

3B Scientific

Shortcomings include:


Main equipment used for two of the two
-
week labs will never
be used again. (water waves, ultrasound)


In our current version of Advanced Lab, students don’t revisit
op amps. Students rarely use them in research.


Because the two
-
week labs are only semi
-
coordinated, the
connection to lecture is different for different students


Conclusions:


Sophomore:


waves & oscillations first semester


quantum mechanics second semester


semi
-
coordinated labs


High level of student interest


Students know what they’re getting into when they major.


First semester labs continue building a good foundation of
experimental skills and intuition.


Helpful to have a connection between lab& lecture, but exact
coordination is not necessary, or even always preferred.