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CD Spectroscope
Using a shoebox and any compact disc, students
may construct a no-cost spectroscope. Functioning as a diffraction grating,
the disc's pitted surface separates incident light into its component
colors. Both emission and absorption spectra are observable using this
easily constructed optical instrument.
As the figure indicates, the spectroscope
consists of a CD mounted diagonally at one end of a shoebox. The CD may be
held in place with either a small piece of tape or by inserting it in a slit
cut in the bottom of the shoebox. A second narrow slit, approximately 5-cm
long and 5-mm wide, is cut in the shoebox lid. Situated over the CD and
parallel to the width of the shoebox, this aperture admits the light to be
analyzed.
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At the end opposite the CD a viewing window,
roughly the size of a postage stamp, is cut in the shoebox's end panel.
Trial and error is used to obtain the optimal spectral display when
positioning the CD.
Placing a plastic petri dish over the slit in the top of the shoebox permits
the examination of absorption spectra (see figure). When placed in the petri
dish, virtually any colored solution will produce dark stripes on a
continuous incandescent spectrum. Wakabayashi, et al 1. suggests trying
solutions of chlorophyll, cobalt chloride and potassium permanganate.
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The plan for the spectroscope shown to the
left, was inspired by a design that appeared in an article in the Journal
of Chemical Education.
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"We recently used the CD Spectroscope as an
extra credit assignment. The evaluation rubric used is as follows:"
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Spectroscope construction - 2 pt.
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Correct spectra key showing spectra of five
different light sources (You might consider incandescent sources, standard
fluorescent lights, various neon lights, sodium and mercury street lights,
and new high intensity car headlamps.) - 2 pt.
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Spectra of additional sources - 1 pt/each
(up to 3 pt)
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Attractive exterior (e.g. decorative
covering, clever spectra key display, spectroscope label, etc.) - 2 pt.
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Signature of parent(s) or guardian(s)
verifying that you have demonstrated your spectroscope and explained its
operation to them - 1 pt.
The reaction by students and their parents to
this device has been amazing! Students enjoyed observing the spectra of
light sources found outside the classroom. Parents, recently visiting school
for annual parent-teacher conferences, were clearly thrilled about their
child's involvement in physics.
Chris Chiaverina, New Trier High School
Reference:
1. Wakabayashi, F; Hamada, K.; Sone, K.; J.
Chem. Educ. 1998, 75, 1569
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| 12 Volt
Electricity
Figuring Physics
 
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My favorite demo with electric circuits is
the car battery with extended terminals. The extended terminals are
simply a pair of rigid rods (welding rods is what I use). They are
easily inserted and removed when female connectors are permanently
fastened into the battery terminals. Alligator clips at the ends of
lengths of wire allow bulbs to be connected to the terminals, showing
series and parallel circuits. It is easy for students to see the
usefulness of circuit diagrams that look so much like the demo itself.
In the sketch to the right we see how an ammeter can be connected to
read the line current.
Three identical lamps of resistance 12
ohms are connected to the 12 volt battery as shown.
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1.What
is the current in each lamp?
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2.What
is the voltage across each lamp?
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3.What
is the power dissipated in each lamp?
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4.How
does the power dissipated in Lamp C change if Lamp A is unscrewed?
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5.What
happens to the power dissipated in Lamp A if Lamp C is unscrewed?
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1.By
Ohm’s Law, Lamps A and B have 0.5 A in them. Lamp C has 1.0 A.
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2.Voltage
across Lamps A and B is 6v each (12v across both). Voltage across Lamp
C is 12v.
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3.Power
in A is 3w, and likewise, 3w in B. Power in C is 12w.
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 Paul G. Hewitt - Conceptual
Physics |
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Simple
Standing Wave
For little over a dollar, you can construct a standing wave
device that may be used for
demonstrations or quantitative measurements. The standing waves produced by
this simple apparatus must be witnessed to be believed.
Materials:
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1 - 1 ½ v electric motor
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1 - AA battery
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1 - ~1 ½ length of 3/8" dowel
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1 - ~1 meter length of string or cord
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3 - 2" lengths of insulated wire
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tape (electrical, masking, etc.)
Construction:
Form vibrator unit by attaching battery to
motor with tape.
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 Solder
2" leads to the ends of the battery. Solder one of these leads to an
electrical contact on the motor. Solder third lead to the other contact on
the motor.
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Drill ~1/16" hole close to end of dowel rod
segment. Attach dowel rod segment to motor shaft. Friction should keep
dowel rod on motor shaft.
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Tie string or cord to convenient point on
vibrator unit.
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To activate vibrator, twist free ends of
leads together. You can also use a AA battery holder as an option. Then
you can just insert the battery to make the connection.
I. Demonstrating Standing Waves
II. Determining Wave Speed - Method I
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Establish standing wave on the string.
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Measure the distance between adjacent nodes.
Multiply this distance by two to obtain wavelength of disturbance.
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Use a strobe light to measure frequency of
wave.
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Calculate wave speed from v=f·λ
III. Determining Wave Speed - Method II
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Use balance to find mass of vibrator unit
and mass of a string sample.
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Calculate weight of vibrator in newtons.
This equals tension in string.
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Find linear density of string (µ=
mass/length).
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Calculate wave speed from v= √T/µ.
Chris Chiaverina, New Trier High School |
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Bernoulli Bag
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The long plastic bag demo nicely illustrates Bernoulli’s principle. If you
were to blow it up by placing it firmly to your mouth, many lung-fulls of
air would be needed. But when you hold it in front of your mouth and blow,
air pressure in the stream you produce is reduced, entrapping surrounding
air to join in filling up the bag. So you can blow it up with a single
breath! This is especially effective after your students have counted many
of their own breaths in attempting to fill up the bag!
Paul G. Hewitt - Conceptual Physics |
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Talkie Tapes
The Talkie Tapes demonstrated at the Physics
Demo Show were created specifically for the 2002 NSTA National Convention.
Additional tapes are available and can be ordered here. All the
tapes say "Science is Fun!" and they are in limited supply, so it
will be first come, first served.
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How to use them:
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Attach the notched end of the Talkie Tape
to a sheet of paper, plastic cup, balloon, etc. with a piece of tape. You can
also punch a small hole in the bottom of the plastic cup and then tie the
pointed end in a knot.
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Slide your thumbnail down the grooved side
of the strip and listen carefully. The strip will talk!
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That's it. No Player. No Batteries. Plays
for years. Plays anywhere!
What's going on:
When a conventional phonograph record is made, a metal cutting needle cuts a
squiggly groove in the plastic. The wavy groove corresponds, or is
analogous, to the sound wave making the needle vibrate. That is why this
technology is called analog recording.
When a phonograph record is played, the needle, or stylus, vibrates as it
passes through the grooves on the record's surface. These vibrations
correspond to the original sound that made the cutting needle move. The
vibrating playback needle is connected to a small electrical generator (a
cartridge) to produce an electrical signal. This signal is then amplified
and sent to a loudspeaker.
With Talkie Tapes, the recorded information is spread out along a 24"
red plastic strip. On one side of the strip is a series of ridges and pits.
These high and low points contain information about frequency and loudness
of the sound that was used to produce them. During "playback", your
thumbnail takes the place of the needle. The sound is amplified by forcing
something with a larger surface area (a cup, paper, balloon,
etc.) to vibrate. This vibrating surface, in turn, moves the air molecules
that carry the sound to your ears. In this case the cup is used to amplify
the sound wave. You can also bite the end of the tape and your head will act
as the sound box.
Make your own record play-back device:
Get a large piece of poster paper and roll it into a cone. (like a dunce
cap). Then take a needle (or straight pin) and push it through the pointed
end of the cone. You will also need an old turntable or kid's record player.
Get an old record (you can find these at garage sales or second hand shops)
and place it on the moving turntable. Carefully set the needle on to the
record, gently holding the cone. You'll have no trouble hearing the
recording. You can also simulate this sound reproduction by flicking the
needle with your finger. Your students will be amazed how loud it is. Be
sure you tell your students not to try this with their CD's! That's a
completely different process. Don't laugh, you'd be surprised!
Chris Chiaverina, New Trier High School |
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Rainbow Sticks
Watch for this product in the 2003 Arbor Scientific catalog!
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This apparatus consists of a
sphere that represents a raindrop, along with three colored dowels. One
dowel is white, representing a ray of sunlight. Another is red, representing
a ray of red light, and another blue for a ray of blue light. The angles
between the dowels,
show the angles between incoming sunlight and
outgoing refracted and internally reflected red and blue rays of light. A
volunteer crouching in front of your chalkboard shows the class how the only
drops that cast light to him or her originate in drops along a bow-shaped
region. Hence the geometry of the rainbow’s bow shape.
Paul G. Hewitt - Conceptual Physics |
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UV
Potpourri
These beads are sensitive to UV light and change from white to an array of
bright colors when they are exposed to sunlight or UV rays. Take them
back indoors and they return to a white color. Great addition to your
demos on light and color.
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Unfortunately,
we ran out of time before we could get to this demo. So here is a link to a
work sheet for your students for identifying different sources of
Ultraviolet Light.
Students
Worksheet (Word .doc Format)
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Atmospheric Pressure Mat
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The rubber mat with the 50-gram hook is my favorite for demonstrating
atmospheric pressure. It originates with John MacDonald of Boise State
University. A sheet of soft rubber with any handle at its center will do.
The one John devised consists of a square sheet about a foot on each side,
with a 50-gram mass hanger poked through the center. Toss the rubber sheet
on any perfectly flat surface—best on the top of a lab stool. Picking the
rubber up by a corner is an easy task, because the air gets under it as it
is lifted. But lifting it by the middle is another story. As the middle is
raised, a low-pressure region is formed because air cannot get in. The
rubber sheet behaves as a suction cup, and the entire stool is lifted when
the handle is raised.
Paul G. Hewitt - Conceptual Physics |
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Einstein Dominoes
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We ended up not showing this demo at the show because the turn out of
teachers was so large it would have been very hard to see. But here's the diagram
for setting up dominoes in such a way as to see Einstein's face.
Chris Chiaverina, New Trier High School |
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Energy
Ball
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Make a connection with your
students!
This very cool device consists of a 1.5-inch
ball with two small metal electrodes. When the two electrodes are touched
simultaneously, the ball flashes and makes a strange tone. The Energy Ball
utilizes a field effect transistor so even the slightest conduction between
the two electrodes activates the Sphere. The Energy Ball is completely
self-contained and requires no additional batteries or energy source. It is
often used to demonstrate closed and open circuits, just line up your
students in different "circuits" and complete the connection.
Chris Chiaverina, New Trier High School |
This is the product Chris used
when he had a number of teachers on stage, showing different ways
to make a "human circuit". |
