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Preliminary Introduction
8.2 Communication
8.3 Electrical
8.4 Moving About
8.5 Cosmic Engine

 

CONTENTS

 

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.

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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.

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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.

 

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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

Distance of source from Geiger Tube (cm)

Radioactive Source

 

Alpha (Counts/30s)

Beta (Counts/30s)

Gamma (Counts/30s)

1.0

 

 

 

2.0

 

 

 

3.0

 

 

 

4.0

 

 

 

5.0

 

 

 

No. of sheets of shielding covering source

Alpha (Counts/30s)

Beta (Counts/30s)

Gamma (Counts/30s)

Aluminium 1

 

 

 

Aluminium 2

 

 

 

.

 

 

 

.

 

 

 

.

 

 

 

Lead 5

 

 

 

 

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.

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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://astronomy.org.au/amateur/amateur-societies/australia/

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

NAME OF OBJECT

DESCRIPTION

 

Moon

Our natural satellite.  Mean distance from earth 384 400km.  A moon filter was added to the eyepiece lens to reduce glare.  Craters, mountains and mare (seas) were clearly visible with the low power 25mm eyepiece.  Detail inside craters was visible.  For instance some craters were seen to have other craters inside them.  Some craters had mountains inside them.  Crater Plato was identified.  This is about 100km x 100km in dimension.  Crater Copernicus was identified.  This is 93km x 93km in dimension and about 3760m high.  Crater Tycho was identified.  This is 84km x 84km in dimension and about 4800m high.  It contains a central mountain about 1500m high.  Best views of Moon features were along the terminator (the line separating light from dark).

 

a-Centauri

Triple star system in the constellation Centaurus.  a-Centauri is the bottom pointer of the Southern Cross.  It was observed as a bright binary star a-Centauri A and a-Centauri B, these stars being separated on average by about the distance from the Sun to Uranus.  They are about 4.3 light years from earth.  The third member of the system, a white dwarf called Proxima-Centauri is the closest star to earth at 4.2 light years and orbits a-Centauri A & B at about 13000AU.  It was not observed.

 

a-Crucis

A binary of equal blue-white stars about 370 ly from earth and found in the constellation Crux (the Southern Cross).  The two stars are separated by a distance of about six times the diameter of our solar system.  Each of the stars is about one and a half to two times the size of our Sun.  The stars were observed as very bright, bluish tinged points of light, clearly separated by some distance.

 

b-Crucis

A blue-white giant star about 490 ly away and found in the constellation Crux (the Southern Cross).  It is about five times the sun’s size.  It is also a variable star – its brightness pulsates slightly.  It was observed as a very bright, bluish tinged point of light.

Betelgeuse

Supergiant Red Star in constellation of Orion.  Distance from earth is between 400 and 1400 light years.  Its distance & luminosity are not yet precisely determined.  It was observed as a bright, orange-red point of light – thanks to Brad who found it through the tree.

 

Jupiter & 4 moons

Planet.  Mean Distance from Sun: 5.5AU or 778 million km.  Jupiter was observed in the eastern to northern sky.  Two horizontal brown bands were observed above & below the equator.  Above, below & between these bands are regions that appear yellowish-white in colour.  The four Galilean moons were clearly observed.  A diagram of Jupiter and its moons was drawn.

 

Saturn & 3 moons

Planet.  Mean Distance from Sun: 9.5AU or 1427 million km.  Saturn was observed in the northern to western sky, directly below the constellation of Orion.  The planet’s disc was clearly visible – a whitish sphere with some dark banded markings visible.  The ring system was also observed.  Two distinct sections of rings were visible separated by the dark Cassini Division.  The rings were very well tilted allowing easy observation.  Three moons were visible as faint points of light.  A diagram was drawn of Saturn and its moons.

 

Jewel Box Open Cluster

NGC 4755, the Jewel Box, is an open cluster of stars about 7600 light years from earth.  It is located about 1o SE of b-Crucis in the constellation Crux (the Southern Cross).  Many bright, coloured stars were observed – blue, orange-red, red, yellow and white – probably in excess of 60 to 70 stars in all, across 10 arc minutes of sky.  The brightest stars are 4 blue supergiants & 1 red supergiant.

 

Great Nebula in Orion

M42 (Messier Object 42) or NGC 1976.  Distance from earth is about 1500 light years.  The Great Nebula is a huge diffuse nebula in the constellation of Orion, roughly NW of the top star in the belt of Orion covering an area of sky of about 90 arc minutes by 60 arc minutes.  A greyish-white cloud of gas and dust was observed.  Several stars were visible shining through and around the edges of the cloud.  The Trapezium Open Cluster of newly formed stars was clearly visible.

 

 

Eta Carina Nebula

 

 

 

NGC 3372.  Distance from Earth is about 7500ly.  Masses of bluish-grey nebulosity rifted by dark dust-lanes and patches, and highlighted by crowds of faint stars.  Several small clusters were observed containing hot O and B type stars.  The nebula was located at about 8.30pm approximately a hand-span north-east of a-Crucis and just a little way north-west of q-Carinae.

 

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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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