Tuesday, 22 April 2014

Testing plastic bag (polymer) strength

This experiment will let you compare the strength of carrier bags provided by different retailers.


Plastic bags from different supermarkets
Two tables
Four G clamps
Four wooden battens


Cut a 30cm square from the plastic bag.
Place one edge between two wooden battens and clamp to the edge of one table firmly with two of the clamps.
Repeat with the opposite edge and clamp to the other table.
Measure how far the tables are apart and make sure this is the same for each test.
Add masses 100g at a time to the centre of the plastic sheet until it breaks and record the mass used.
Repeat for each plastic bag from the different supermarkets.


Be careful to stand well back when adding masses as the plastic may break unexpectedly and the masses could fall on your feet. Also make sure you are using heavy enough tables that will not be pulled over by the mass in between them.

Wednesday, 19 March 2014

Diffusion in egg white

This experiment will allow you to investigate how the rate of diffusion into egg white is affected by the concentration of the solution they are suspended in.


Food colouring (red or black will work best)
6 egg whites
Ice cube tray
Steamer or hot water bath
Measuring cylinder
6 beakers
Paper towels


Distribute the egg white into the ice cube tray so that the wells are filled.
Either in a steamer or water bath (taking care not to let the water get into the wells) heat the egg white until it solidifies. Do not use a microwave as the heating is too vigorous and will result in air bubbles forming in the egg white.
Gently remove the egg white from the trays and use the ruler and knife to cut the egg white into uniform 1cm cubes - you should aim for at least 12 cubes.
Make 6 different concentrations of food colouring solution using 100ml of water and 1, 2, 3, 4, 5 and 6 ml of food colouring.
Place each solution in a different beaker and add at least two cubes of egg white.
Leave in the solution for 3 hours then remove the egg white cubes and dry the outside using the paper towels.
Carefully slice the cube in two and use the ruler to record how far the colour has penetrated into the cubes in each solution.


Steam or hot water used to solidify the egg white could cause a scald so take care to let the ice cube tray cool before handling.
Any spills should be cleared up as quickly as possible. Any breakages should also be carefully cleared up using a dustpan and brush.
Care should be taken when using the knife to make sure you do not cut yourself.

Ball bounce height vs surface material


Squash ball
Metre stick
Clamp and stand
Different materials (e.g. carpet, lino, cork, wood, rubber)

NOTE: ideally materials should all be the same thickness.


Place one material on the floor and use the clamp and stand to support the metre stick next to it.
Next drop the ball from the top of the metre stick onto the surface and record the maximum height to which the ball bounces.
Repeat this experiment at least another two times.
Change the material and carry out another three tests.

Risk Assessment

Ensure the ball does not roll away into an area where it could get underfoot and cause a fall.
When setting up the metre stick make sure it is clamped securely so it won't fall onto people carrying out the experiment.

Squash Ball bounce height vs temperature

In this experiment you can investigate how the height at which a squash ball bounces is affected by the termpaerture of the ball.


5 squash balls of the same type
Water bath with temperature control
Paper towels
Digital video camera (high speed if possible)
Metre stick with clear markings
Clamps & stands


Place the squash balls into the water bath set to 20 degrees Celcius and ensure they are completely submerged.
Leave the balls in the water for at least 5 minutes to ensure the temperature of the rubber has stabilised.
Set up the metre stick so one end is on the floor using the clamp and stand to support it.
Set up the video camera so there is room to drop the balls between it and the metre stick and so that it has a clear view of the metre stick scale.
Use the tongs to remove one rubber ball and quickly blot off any excess water using a paper towel.
Start the video camera and drop the ball from level with the top of the metre stick.
Repeat with each of the remaining 4 balls.
Stop the camera and note the recording time.
Increase the temperature of the water bath by 10 degrees and replace the balls in it, again for at least 5 minutes.
Repeat a new recording of the balls being dropped.
Continue increasing the water bath temperature and recording the balls being dropped at 10 degree intervals until you reach at least 60 degrees.
Finally review the tape to record the maximum height each ball reached on its first bounce.

Risk assessment

Slips and falls may occur if the floor gets wet, this should be prevented by drying the balls carefully and by mopping up any wet areas quickly.
At higher tempertures there is a risk of scalding from the water. Tongs should always be used to remove the balls from the water bath to prevent contact with the skin. Additionally the experiment should not be run at a water bath temperature higher than 60 degrees Celcius

Wednesday, 27 November 2013

Transformers - voltage & coil ratios.


To investigate how the ratio of number of turns on the primary and secondary coils affects the potential difference across them.


laminated iron C cores and holder
Insulated wire for winding
Power supply (12V a.c.)
Digital Multimeter or a.c. voltmeter
Connecting leads & crocodile clips


Wind each side of the C core with 50 turns of wire.
Connect one side to the a.c. power supply set to 6V - this is the primary coil.
Connect the other side to the multimeter (set to measure a.c. voltage) or the a.c. voltmeter - this is the secondary coil.
Join the C cores using the holder.
Switch on the power supply and record the reading on the meter, then turn off the power supply again. Repeat the reading twice more.

On the side connected to the multimeter UNWIND 5 turns.
Take another three readings for the voltage.
Continue unwinding and taking readings until you have only 5 coils on the secondary side of the transformer.

Risk assessment

Wires may become hot if current is allowed to flow for too long due to low resistance so the power supply should not be left on. If it is left on too long wires should be allowed to cool after the power is shut off before moving the equipment.

There is a risk of electric shock with this experiment.
It is very important to start with the maximum number of turns on the secondary and then unwind it. This prevents any stepping up of the voltage which could cause sparking.
The current will increase as the voltage is stepped down so all changes should be made to the secondary coil without the power being turned on.
The equipment should not be touched when turned on.
Anyone with a heart condition or who has a pacemaker should be especially careful.

Tansformer power measurements

This experiment will allow you to perform a basic investigation of the power transfer & efficiency of a simple transformer.


Power supply (12V a.c )
12V bulb
Variable resistor
Two a.c Voltmeters
Tw a.c Ammeters (multimeters could be used)
Connecting leads with croc clips
Wire for winding (laminated or insulated)
Iron rod 15 - 20 cm long


From the power supply attach the variable resistor and one ammeter in series. Create a primary coil of fifty turns around one end of the iron rod using the winding wire and use croc clips to connect this pimary coil in series with the ammeter and variable resistor back to the power supply. Connect one voltmeter in parallel across the primary coil.

Create a secondary coil at the other end of the iron rod, again using fifty turns. Using crocodile clips connect the bulb and the second ammeter in series with the secondary coil and connect the voltmeter in parallel to teh secondary coil.

With the variable resistor turned completely one way not the readings on all of the meters.

Turn the variable resistor and take readings in five to ten different positions until the variable resistor reaches the other limit of rotation.

Repeat twice more, using the variable resistor to give your the same values for current and voltage on the primary coil each time.


Find the mean readings for each step and then use the equation P = I V to find the power on the primary and the power on the secondary.

Plot a graph of the input and output power and describe any relationships you notice. Why is there a discrepancy in the power between each side?

Sunday, 2 June 2013

Reflection from a curved mirror

This experiment uses a laser to determine the focal point of a curved mirror on its concave surface.

On a piece of paper draw a line which will be your principal axis. Place the mirror at one end of this line so that the centre of the mirror bisects the line.

Use the laser to shine a ray of light parallel to the principal axis so that it reflects off the mirror. Using a sharp pencil mark the path of the ray on the paper.

Repeat this for a number of different starting positions - the point where all the lines cross the axis is the focal point of the lens.

It should be noted that there are risks using lasers. Care should be taken to choose a laser which is eyesafe at the aperture and to be careful with the laser alignment so that stray reflections are minimised.