Level 3 Practical Investigation Where to start?

Aim This is the purpose of your practical i.e. what it is that you want to find out This is the purpose of your practical i.e. what it is that you want to find out Be specific – don’t use terms like ‘best’ Be specific – don’t use terms like ‘best’ Make a prediction = hypothesis Make a prediction = hypothesis This does not have to be correct! This does not have to be correct! It is quite alright if your experiment DISPROVES your hypothesis. It is quite alright if your experiment DISPROVES your hypothesis. Record a few ideas for initial consideration

VARIABLES After deciding on or while you contemplate your area of investigation, you should consider completing a planning table. After deciding on or while you contemplate your area of investigation, you should consider completing a planning table. It should easily be able to fit onto one side of A4 paper – Use your logbook! It should easily be able to fit onto one side of A4 paper – Use your logbook!

PLANNING TABLE Make note of the variables - these are things that could change while you carry out your experiment.

VARIABLES Some variables may turn out to have no effect at all on the outcome of the investigation. Some variables may turn out to have no effect at all on the outcome of the investigation. Most of these are usually quite trivial and can be ignored. Most of these are usually quite trivial and can be ignored. Sometimes, however, it is important to establish that what appears to be an important variable does not in fact affect the investigation. Sometimes, however, it is important to establish that what appears to be an important variable does not in fact affect the investigation.

VARIABLES

TYPES OF VARIABLES

VARIABLES - examples VARIABLE MEASURING DEVICE UNITS &SYMBOL DISTANCE length length breadth breadth height heightRuler metre (m) centimetre (cm) millimetre (mm)

VARIABLES - examples VARIABLE MEASURING DEVICE UNITS &SYMBOL AREA calculated rectangle area = l x b square metre (m2) square centimetres (cm2)

VARIABLES - examples VARIABLE MEASURING DEVICE UNITS &SYMBOL VOLUME calculated cube volume = l x b x h OR FOR LIQUIDS use a measuring cylinder cubic centimetres (cm3) [1cm3 = 1 ml] millilitres (ml) litres (l)

VARIABLES - examples VARIABLE MEASURING DEVICE UNITS &SYMBOL TIME RATE eg.speed MASS CONCENTRATION TEMPERATURE

VARIABLES - examples VARIABLE MEASURING DEVICE UNITS &SYMBOL VOLTAGE CURRENT ACIDITY [ pH ] LIGHT INTENSITY

VARIABLE For most Higher Level investigations there will be a choice of variables. For most Higher Level investigations there will be a choice of variables. If there is not suitable Higher Level knowledge to use for a prediction then choose another variable. If there is not suitable Higher Level knowledge to use for a prediction then choose another variable. You need to be able to produce a good prediction You need to be able to produce a good prediction

DEPENDENT VARIABLE The Dependent variable is nearly always a continuous variable. The Dependent variable is nearly always a continuous variable.

INDEPENDENT VARIABLE A categoric variable is normally a poor choice. A categoric variable is normally a poor choice. They are often the simplest variables to investigate but it is often impossible to generate a worthwhile prediction. They are often the simplest variables to investigate but it is often impossible to generate a worthwhile prediction. In general, don't even consider a categoric variable. In general, don't even consider a categoric variable.

INDEPENDENT VARIABLE A Discrete variable can get top marks, although you need to double check that what you think is a discrete variable is not in fact a continuous variable. A Discrete variable can get top marks, although you need to double check that what you think is a discrete variable is not in fact a continuous variable. Supposing you were carrying out an insulation experiment and decide upon the number of layers of insulation as the independent variable. You would not gain top marks. What you should do is measure the total thickness of the insulation. Thickness is a continuous variable and would give access to the top marks. Supposing you were carrying out an insulation experiment and decide upon the number of layers of insulation as the independent variable. You would not gain top marks. What you should do is measure the total thickness of the insulation. Thickness is a continuous variable and would give access to the top marks.

INDEPENDENT VARIABLE The best choice is often a Continuous variable. The best choice is often a Continuous variable. This allows you to put together a quantitative prediction. This allows you to put together a quantitative prediction.

COMPLEXITY If the investigation is too simple it will be impossible to gain top marks. If the investigation is too simple it will be impossible to gain top marks. If it is too complex you may run out of time or end up with poor quality results. If it is too complex you may run out of time or end up with poor quality results.

TIME This is probably the most important consideration. This is probably the most important consideration. If you do not budget carefully you will run out of time. Look carefully at what is involved to set-up and carry out the experiment, including all the repeats. If you do not budget carefully you will run out of time. Look carefully at what is involved to set-up and carry out the experiment, including all the repeats. Estimate the total time. Is it feasible? It is no good having a brilliant plan if you only manage to collect half the required results. Estimate the total time. Is it feasible? It is no good having a brilliant plan if you only manage to collect half the required results.

RESOURCES Check that all the equipment you need is available. Check that all the equipment you need is available. Check that all the resources, such as chemicals, are available in the amounts you require. Check that all the resources, such as chemicals, are available in the amounts you require.

RANGE OF THE INDEPENDENT VARIABLE The range of values you decide to investigate must be sufficient to give your prediction a good test. The range of values you decide to investigate must be sufficient to give your prediction a good test. This means as big a range as is practical for you to carry out. This means as big a range as is practical for you to carry out. You need at least 5 sets of data, 8 would be more realistic, more where results can be obtained quickly. You need at least 5 sets of data, 8 would be more realistic, more where results can be obtained quickly. In general, take as many measurements as you have time for. In general, take as many measurements as you have time for. You need enough measurements such that there is no doubt that your graph shows a true and accurate trend. You need enough measurements such that there is no doubt that your graph shows a true and accurate trend.

RANGE OF THE DEPENDENT VARIABLE Don't forget to check that you can still measure the outcome over all the values of the independent variable you intend to use. Don't forget to check that you can still measure the outcome over all the values of the independent variable you intend to use. If the dependent variable goes off the scale you may be able to tweak some of the control variables to reduce it to more manageable values. If the dependent variable goes off the scale you may be able to tweak some of the control variables to reduce it to more manageable values.

REPEATING Readings must be repeated a suitable number of times. Readings must be repeated a suitable number of times. There is no magic rule for how many times you must repeat readings. There is no magic rule for how many times you must repeat readings. If repeat readings are very similar twice would be enough. If repeat readings are very similar twice would be enough. Most people take 3 sets to be on the safe side. Most people take 3 sets to be on the safe side. If you get two similar and the third is way off you know something has gone wrong and you can double check it to eliminate the bad result. If you get two similar and the third is way off you know something has gone wrong and you can double check it to eliminate the bad result. If there is a big variation between results then you must take more repeats to get a good average. If there is a big variation between results then you must take more repeats to get a good average.

RANGE OF THE DEPENDENT VARIABLE Don't forget to check that you can still measure the outcome over all the values of the independent variable you intend to use. Don't forget to check that you can still measure the outcome over all the values of the independent variable you intend to use. If the dependent variable goes off the scale you may be able to tweak some of the control variables to reduce it to more manageable values. If the dependent variable goes off the scale you may be able to tweak some of the control variables to reduce it to more manageable values.

At all times, you should be recording your ideas and findings in your log book!