Monday, 28 May 2012

Photosynthesis Rate vs Light Intensity in Elodea


LED full spectrum lamp
Boiling tube
Clamp & stand
Sodium bicarbonate (Baking Soda)
Elodea pond weed


Make up a 0.2% solution of the Sodium Bicarbonate and water to provide a source of Carbon Dioxide for the Elodea.

Fill the boiling tube with the solution and add a piece of Elodea such that there is 2cm of solution present above the Elodea. Clamp this in place making sure the that clamp obscures as little of the Elodea and solution as possible. Gently tap the tube to dislodge any gas introduced to the tube with the Elodea.

Set up the LED lamp at a 5cm distance from the side of the boiling tube. A normal lamp can be used, however the temperature increase caused by using an incandescent lightbulb will introduce an error into your experiment as temperature also affects the photosynthesis rate. For improved results ambient lighting should be kept constant or the experiment should be done using the LED lamp as the only source of light.

Wait for the Elodea to start producing bubbles. Start the stopclock and count the bubbles produced over a one minute period. Repeat measurement a further two times.

Move the lamp further away from the Elodea by between 5cm and 10cm depending on how many measurements you wish to take. Wait two or three minutes for the rate of bubble production to settle and then repeat the measurements of the bubble count over a minute.


Light intensity obeys and inverse square law - this means that if you double the distance you quarter the intensity. To analyse your results you should square the distance between the lamp and the Elodea and then take the inverse of this number to plot the x axis of your graph. By plotting this against the number of bubbles produced you will be able to determine the relationship between light intensity and photosynthesis rate.

Rate of photosynthesis & light intensity

This experiment will need careful setting up to give you valid results.

First you will need to source some pond weed, Elodea or Cabomba will work. You will also need a large beaker or ice cream tub and a clear measuring cylinder - a glass one would be best. Finally you will need a lamp, a ruler and a stopclock.

The pond weed should be placed into the measuring cylinder and then this should be filled with water in the ice cream tub and then inverted so that the measuring cylinder is full of water. Set the lamp up at a known distance from the pond weed and start the stop clock.

It is up to you how long you leave the equipment set up like this, however the longer you can leave it the more gas will be produced. You will need to record the volume of gas produced when you return to the experiment.

Replace the water in the measuring cylinder set up, move the lamp to a new distance from the pond weed and then leave the equipment for the same time as before.

Repeat again for at least one more distance between lamp and pond weed, however if you can do more then do.

If you are leaving the equipment set up for a significant length of time unattended you will need to make sure that the measuring cylinder is supported - especially if it is made of glass. You should also ensure that there is nothing resting on or near the lamp as depending on the type of bulb used the lamp could become hot after extended periods of operation.

Hookes Law 2 - elastic bands

Equipment list

Elastic bands
Clamp & stand


Set up the clamp and stand so it holds the ruler and the elastic band.
Place the foam under the elastic band and put on the goggles.
Add masses to the elastic band and measure how much it stretches by as you add each mass.
Should you overextend the elastic band and it breaks the foam will catch the masses and any flying pieces of rubber will not go in your eyes.
Record your results in a table.
If you have time repeat your experiment a couple more times and calculate an average of the extensions.
Plot a graph of your results.


Try the experiment again with two and three elastic bands.
Try different configurations of the elastic bands, knotting them together lengthways, or placing them side by side.
How does this affect the shape of the graph and why?

Sunday, 13 May 2012

Hookes law 1


This experiment will allow you to find the spring constant of the spring you are using and, if graphed correctly allow you to work out the energy transferred into the spring when it is deformed past the limit of proportionality.


Clamp stand
Boss head
Extending tape measure
Metal spring
Mass hangers (kilograms in 100g divisions)


Set up the equipment as shown in the diagram below
Measure the length of the spring with no mass attached
Add a 0.1kg mass, measure the extension of the spring
Keep adding masses and measuring the extension until the spring stretches past the limit of proportionality (it will not return to its original length in this case)
Remove the masses one at a time until all the masses are removed.


Calculate the force applied (1kg = 9.8N of force)
Plot a graph of the results with the Extension on the x axis. Use separate colours for adding and subtracting masses so you have two lines.
The slope of the linear part of the graph is the spring constant for the spring.
The area between tho two lines represents the energy that has been transferred to the spring.

Exothermic reaction of Calcium Oxide 2


calcium oxide powder
stirring rod
5 polystyrene cups


Half fill each of the cups with water so that they are all full to the same level
Record the temperature of the water
Add 1 spatula of CaO to the first cup, 2 spatulas into the second one etc and stir to make sure it all dissolves
Wait 1 minute and measure the temperature in all the cups again
Rinse all the cups out and repeat the experiment another two times
Calculate the average temperature rise for each cup


CaO is an irritant and contact with skin should be avoided.

Exothermic reaction of calcium oxide 1


To see how the mass of calcium oxide affects the temperature change produced in a reaction with water


Adding Calcium Oxide to water produces an exothermic reaction as aqueous Calcium Hydroxide is formed. The total energy released will increase as more bonds are broken by using a greater mass of Calcium Hydroxide

CaO powder
De-ionised water
50 ml measuring cylinder
Insulating beaker
Balance (.01g resolution)
Temperature probe and data logger
Stirring rod


In an insulating beaker combine 50ml of water with 1g of CaO
Stir and record the maximum temperature reached using a temperature probe and datalogger
Repeat the experiment by using fresh water and increasing the mass of CaO used by 1g


As CaO will react exothermically with water care should be taken to avoid contact with skin where reaction with moisture could cause irritation and in extreme cases burns.