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Practical No. 1 – Spectrum
of Hydrogen and Mercury
Aim: To observe the emission spectrum of hydrogen and mercury. Method: Set up a variable deviation spectrometer with a diffraction
grating mounted on the spectrometer table.
Connect first a hydrogen and then a mercury discharge lamp to an
appropriate high voltage source and observe & draw the emission spectrum of
each element.
Results: Should include labelled diagrams and a written description
of each spectrum. Discussion: If used in the Cosmic Engine topic, I would omit the
discussion from student reports. When
used as a mandatory prac in the From Quanta To Quarks Option, students
can write a discussion that shows that they understand HOW the emission lines
are produced. Note that this prac can easily be extended to include a measurement of the wavelength of one or all hydrogen emission lines and a subsequent comparison with literature values. The Teacher would need to provide the additional information & formula (nl = d sinq) to enable this measurement to take place. Conclusion: A brief statement of what was achieved in this experiment.
Practical No. 2 –
Absorption of Sodium Light
Aim: To observe the absorption of sodium light by sodium vapour. Method: Sprinkle sodium chloride crystals into the flame of a
Bunsen burner that is sitting directly in front of a sodium light source (eg
sodium discharge lamp). A shadow of
the flame will appear on a white cardboard screen on the opposite side of the
Bunsen to the sodium light source. Results: A simple, labelled diagram showing the shadow of the flame
and a brief written description would be all that is required. Discussion: An explanation of what was observed.
This should indicate that the student understands that the sodium vapour
produced in the Bunsen flame absorbed the sodium light from the discharge tube,
thus creating a shadow of the flame. Some
comment may be made on the fact that when an elemental vapour absorbs light, it
absorbs those same wavelengths that it would normally emit when heated to high
temperatures such as those in a discharge lamp.
Some attempt may also be made to comment on the absorption spectra of
stars and the usefulness of such spectra. Conclusion: A very brief statement of what was achieved in this experiment.
Practical No.3 - Inverse Square Law for Light
You may like to do this experiment in Cosmic Engine rather than The World Communicates topic. If so, follow this Link & use the back arrow of your Browser to come back here. Inverse Square Law for Light Prac.
Practical No. 4 – Natural
Nuclear Radiation
Aim: To observe the relative penetrating abilities of a, b and g radiation through air, lead and aluminium. (Syllabus point 8.5.4 Column 3 dot point 1) Equipment: Sources of a, b and g radiation – eg radium-226 for alpha, strontium-90 for beta and cobalt-60 for gamma Retort stand Geiger-Muller tube & Geiger counter Several pieces of lead & aluminium, each of identical thickness Metre rule Health
Warning:
No student must touch any of the radioactive samples or equipment during
this demonstration. The Teacher
must wear protective clothing in the form of a lab coat and plastic gloves.
Handle the radioactive samples with tweezers.
Only one sample at a time should be outside the radioactive sample
storage box. Place paper towels over the bench area you are going to use.
Throw theses away at the end of the experiment.
Wash the bench area that was used & your hands thoroughly at the end
of the experiment. Method: 1.
Set up the equipment as shown in the following diagram. 2. With no radioactive source on the base of the retort stand, measure & record the background radiation count for 30 seconds. You must subtract this figure from all counts taken in the rest of the experiment. 3. Place the alpha source on the base of the retort stand directly under the Geiger-Muller tube. Arrange the Geiger-Muller tube, henceforth called the detector, to be 1cm above the source. Record the number of counts for a 30 second time period. This is a measurement of the alpha radiation’s penetration ability through air. 4. Repeat this procedure with the source-detector distance at 2cm, 3cm, 4cm & 5cm. 5. Next set the detector at 2cm from the source. Place 1 sheet of aluminium over the top of the source and record the count for 30 seconds. Add another sheet of aluminium over the source and repeat the count measurement. Proceed in this fashion with up to 5 sheets of aluminium. 6. Then repeat step 5 using lead sheeting instead of aluminium. 7. Now repeat the whole sequence of steps from 1 to 6 using the beta source. 8. Again repeat steps from 1 to 6 using the gamma source. Results: Use a table similar to the following to record your results. Table No.1: Counts Recorded for 3 Different Radioactive Sources
For one of the sources, say the alpha source, graphs could
be drawn of Counts/30 seconds versus distance from source through air and
Counts/30 seconds versus number of sheets of shielding.
These could be examined for trends. Discussion: Have a careful think about your results.
Maybe estimate the distances through air at which the count from each
different source dropped to half. Does
that tell you anything? Maybe work
out how many sheets of aluminium or lead were required to cause the count from
each different source to drop to half. Does
this tell you anything? Were the
results as expected? Any surprises? If so, how do you account for these? What do the results suggest about the effect on radiation of
the distance travelled through air? What
do they suggest about the effect on radiation of different types of absorbing
material? Can you conclude anything
about the relative penetrating abilities of a, b and g radiation? Would it perhaps be a good idea to increase the count
time in this experiment to produce more statistically meaningful results? Does it matter that the radioactive sources used were
almost certainly not identical in terms of their activity (the number of atoms
of a radioactive substance that disintegrate per unit time – measured in
curies)? Conclusion: A very brief statement of what was achieved in this experiment. Return to Contents
Practical No.5 –
Astronomical Observations
Aim: To use a telescope to observe some features of the night
sky. Equipment (as used at SFX
College – obviously, any decent telescope you can get your hands on will do): Bintel BT 252 Newtonian Reflector on Dobsonian mount. Focal Length: 1250mm Aperture: 250mm (10 inches) Focal Ratio (focal length/aperture): f/5 Eyepieces used in this experiment: 25mm & 9mm Bintel Plössl, fully coated with multi-coatings, 1.25" barrel diameter Magnification with these eyepieces: 50x & 139x respectively Finder Scope: 8x power, 50mm aperture Method: A 10-inch objective Newtonian reflecting telescope on a Dobsonian mount as described above was used to observe examples of planets, stars, open clusters, nebulae and the moon. A brief description was written for each object observed and diagrams were drawn for some of the objects. A diagram of the telescope is shown below.
NOTE:
This prac is best done in small groups, say 6 to 8 students
at a time, to maximise the viewing time for individual students.
Most school yards, even urban ones, will have somewhere appropriate to
set up the telescope where it is reasonably dark with a clear view of the
ecliptic. Set up preferably on
grass, especially in hot weather, to reduce turbulence due to hot air currents
rising from the ground. Again in
hot weather if possible try to avoid looking over the rooves of houses – lots
of hot air currents rise from these as the rooves cool. If you have no access to a decent telescope, contact the local branch of the Astronomical Society. They will often be able to help out by providing a viewing night for students. Go to the following URL to get an appropriate link. When you get there just page down & you will find links to all the Amateur Astronomical Societies in Australia. http://www.astronomy.org.au/ngn/engine.php?SID=1000022&AID=100136
There are many objects that can be viewed depending on time
of year: the moon, the planets (Venus, Mars, Jupiter & Saturn are the
easiest to find & view), stars, open & globular clusters, nebulae,
galaxies, comets (occasionally) and so on.
When organizing a viewing evening, take into account the phase of the
moon. It is good for students to be
able to see a large selection of astronomical objects, including the moon but realize
that if the moon is too full, its fairly intense light will drown out many other
objects in the sky. So, pick a
night when the moon is no more than a quarter full. That way you will still get a reasonably good look at most
other objects you are likely to want to view. A list of objects commonly viewed by students at SFX on
astronomical evenings includes (not all on the one night obviously): the moon,
the planets (Venus, Mars, Jupiter + moons & Saturn + moons), some stars (a-Centauri,
b-Centauri, the
Southern Cross – a, b, g, d
& e-Crucis, Sirius, Canopus, Betelgeuse, Rigel, Antares,
Aldebaran and many others), note that several binary star systems are included,
open clusters (the jewel box, M6, M7, the Pleiades), globular clusters (w-centauri)
and nebulae (the Great Nebula in Orion, the Eta Carinae nebula, the Coalsack
dark nebula). An example follows of the Data Sheet supplied to students after their viewing evening. This can be helpful for students to use during their write-up of the Prac. Astronomical Objects Viewed from SFX Staff Car Park on Tuesday 30/3/04 7.00-9.00pm
Practical
No.6 – Observation of the Sun
Aim: To use a telescope fitted with a solar filter to observe the Sun. Equipment: As for Practical No.5 plus a JMB Type A Solar Filter.
NOTE: Do NOT ever look directly at the Sun even when wearing sunglasses. Your eyes will suffer damage and in most cases this is permanent. NEVER, EVER, EVER look at the Sun through any optical instrument unless it is properly covered with a suitable solar filter and you are absolutely certain you know what you are doing! Permanent eye damage will result almost instantly by making such unprotected solar observations. Method: Set up your telescope with a suitable, safe, solar filter
attached over the objective end of the scope.
Ensure that no finder scope is attached to the telescope or that the
lenses of any finder scope are covered to eliminate any possibility of
accidentally viewing the unfiltered Sun. Aim
the scope by pointing it in the general direction of the Sun, without looking
directly at the Sun at any time, and adjust the scope until the shadow of the
scope is as small as possible. Then
your scope is pointing at the Sun. Make
observations & diagrams of sunspots & faculae.
If you possess a hydrogen-alpha filter use this to observe prominences,
filaments & flares. If you are unsure about observing the Sun, contact your
local branch of the Astronomical Society.
They may be able to assist. See the link above in Practical No.5
for links to all the Amateur Astronomical Societies in Australia. An example diagram of the Sun that students could present
is as follows.
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Last updated:
Bob Emery Catholic Schools Diocese of Maitland Newcastle © 2002