Teachers

Displaying the signals from your TV remote
Connect the Light Gate Receiver to TSA and power the unit.

Hold the TV remote immediately in front of the Light Gate and press a channel button

Observe that the green LED flashes and note that the LED on TSA also flashes.

Now connect a storage scope to the 4mm terminals of the LED which is flashing on TSA.

Observe the pattern.
If you do not have access to a storage scope use an ordinary scope - the pattern can still be seen.

This is a nice simple demonstration applicable to any course in Communications or elementary analog/digital signals.

Speed of Sound Through Wood
Connect your two sound switches to TSA and power the unit

Place the switches facing the ceiling and about 80 cm apart

Put a piece of foam under each switch.

Now place a metre stick so that it lies on top of the two microphones with about 20 cm overhanging from one of the switches.

Select the Fast Timer mode in TSA and carefully reset the Sound Switches.

Tap the metre stick at one end with a toffee hammer or screw driver.

Observe that the time to travel through the wood is much less than the time to travel through air.

Repeat the experiment hitting the metre stick in the vertical direction and also in the horizontal direction and note the different times. This is analagous to s-type and p-type waves.

Speed of Sound in Air
The speed of sound in air is dependent on the temperature. Listed below are the speeds for various temperatures.

It is interesting to ask pupils why sound travels faster through wood than air. Hopefully you will receive answers about the density of the materials and the packing of the particles. Now ask why the speed of sound is faster in hot air compared with more dense cold air.

Introduction to Gradients in Mechanics
Connect your Sound Switches to TSA and power the unit.

Select the Fast Timer mode and place the switches 20 cm apart

Record the time and distance - repeat to get an average.

Now place the Sound Switches 40 cm apart and repeat the above.

Continue in this way until the Sound Switches are 120cm apart (or greater).

Draw a displacement/time graph - note that time is on the x axis.

Find the gradient of the graph.

If the gradient is expressed in m/s then the pupils will recognize this number as the speed of sound. This puts the gradient in a meaningful context for the pupil.

On Your Bike
Using TSA and with a few modifications to a bike it is possible to measure the acceleration of a pupil. 

Strap a piece of dowelling to the crossbar of a bike so that 40cm or more sticks out in front of the bike.

Connect a large double mask made from stiff card to the front of the dowelling. You may find this easier to do before connecting the dowelling to the bike.

If you are using the corridor as the 'speedway' then it is necessary to span the corridor with a light gate at the correct height. Connect a PP3 to run TSA and the Light Gate Receiver. Use a very bright torch with a beam which can be focused ('Mag Light') as the light source and move the source further and further away from the detector until the gap is big enough to cycle through. With a good torch and fresh batteries this is possible. The photodiode in the detector has a daylight filter and this means that it is only the infra red which is being detected. It may be worth while exploring other lamps which give off a reasonable amount of heat if you experience difficulties with a torch - N.B. a laser will not work.

You are now ready to do some Physics. It is interesting to ask the pupil to predict a ball park figure for their acceleration.

What happens to their acceleration as they move further back from the light gate?

What gear gives the best acceleration?

What is the deceleration when the brakes are applied.

It should be stressed that safety is paramount in all the suggestions above, both for the cyclist and the onlookers.

Induced Voltage and di/dt - Disk 4
When this experiment is performed with a Unilab 0.5H air-cored coil an excellent straight line is obtained, the gradient of the graph giving the value of inductance. However on repeating with an iron-core the graph is non linear at the start where the rate of change of current is greatest. The explanation offered in the Teachers' Notes is that the domains are initially arranged randomly and at switch on they take a short time to align themselves. Another suggestion offered is that the equation e = L di/dt is incomplete - it should be e = L di/dt + i dL/dt. Further comments are welcome.

Q/V Relationship - Disk 2
Using this Application the slope of the QV graph gives the approximate value of the capacitor. The relationship E = 1/2 CV² can also be determined from the data set.

Select the graph.

From the Graph Menu select Tools then Extract Area.

Draw an Area/Voltage graph.

Fit a polynomial of degree 2 (i.e. a parabola) to this curve.

The equation should show that Energy (area) is approximately 1/2 CV². You will of course have determined C from the slope of the Q/V graph.

Flash Gun
Connect the Linear light sensor to ALBA and set up the Investigator to take 1000 readings at 1ms intervals. No trigger was used but this could be investigated if desired. When you obtain the graph zoom in on the relevant portion.

Note that if you have the light sensor too close to the flashgun you will saturate the sensor.

Lens Aperture
Set the 12V bulb supplied with the Inverse Square Law Kit immediately infront of the lens of an SLR camera. Open the camera and place the Linear Light Sensor pointing through the lens. Set the speed to 1/30s and the f stop to f5.6.

Set up the Investigator to take 100 readings at 1ms intervals. Set the trigger to 0.05mW/cm2.

Which colour is seen most easily?
This experiment is perhaps best suited for younger pupils.

Place a piece of white paper on the bench and shine an anglepoise lamp or microscope lamp on it. Use the Linear Light Sensor to monitor the amount of reflected light from the paper. Monitor the reflected light using the Meter option in the Investigator software. Now replace the white paper with different colours of paper and determine which colour reflects the light best. This leads to what colours should be worn so that you are seen easily on a dark morning or walking in the mountains.

The experiment could be repeated using materials other than paper. Also try materials with dull and shiny surfaces and/or smooth and rough surfaces.

Falling Magnet
To obtain the results of a magnet falling through a coil as shown in the ALBA Software section of the site try the following:

• Obtain a length of miniature electrical trunking - discard the flat part.
• Push the trunking through the centre of a Unilab coil (1200 - 0 -1200 turns). The trunking acts as a guide for a magnet to fall through the coil.
• Set up the Investigator for 100 readings, 500 microsecond intervals, 5V bi-polar input and a rising trigger (increases by 0.1V).

It matters what pole of the magnet enters the coil first and what way the coil is wound so it may take several attempts to get a rising voltage.

Monitoring the Oxygen as a Candle Burns
For this teacher demonstration you will require:

• a carboard tube with a lid. The tube must be at least 50cm long - this is important - and diameter approximately 8cm.
• a djb microtech oxygen gas sensor.
• a night light or small candle
• matches

Cut a hole in the lid so that the oxygen sensor fits tightly through it.

At the other end of the tube about 5 -10 cm up from the end cut a rectangualr window and cover the window with thick polythene. This window will enable you to see the candle as it burns. You may have to place a small block of wood under the candle so that the candle can be viewed through the polythene window.

Set the Investigateor to take 300 readings at 1s intervals. Light the candle but don't place the tube over the flame just yet. Let the software log the normal oxygen content of the air in the room for say 20s and then place the tube containing the sensor over the burning candle. Ensure that it cannot topple. Typical results are shown below.

Other investigations are possible. Does a wider tube show the same effect? Does the more dense carbon dioxide move the same way in the wider tubes? Please remember not to damage your oxygen gas sensor by putting it too close the the flame. You could of course insert heat sheilds in the middle of the tube!

Monitoring the oxygen content of the gas you breathe out
Connect your oxygen gas sensor to the ALBA Interface.

Use the Investigator software and select Meters and click Use Table checkbox adjacent to it.

You will be asked to give the column data a name and how many decimal places you wish to display on the meter.

On clicking GO the data streams into your Table and percentage oxygen is displayed on the meter. Breathe out over the sensor for a period of 5-10s. Now while the data is still streaming into your Table select the two data columns in your table by clicking once in each of the Headings. Now click the graph icon and you will see a dynamic display of the oxygen/time graph. Breathe again over the sensor. A typical result is shown below. Further investigations could include holding your breath for a short time and then breathing out; vigorous exercise then breathing over the sensor.