Level 3 Practical Level 3 Practical InvestigationInvestigation

Where to start?Where to start?

AimAim

This is the purpose of your practical This is the purpose of your practical i.e. what it is that you want to find i.e. what it is that you want to find out out

Be specific – don’t use terms like Be specific – don’t use terms like ‘best’‘best’

Make a prediction = hypothesisMake a prediction = hypothesis This does not have to be correct! This does not have to be correct! It is quite alright if your experiment It is quite alright if your experiment

DISPROVES your hypothesis.DISPROVES your hypothesis.Record a few ideas for initial consideration

VARIABLESVARIABLES

After deciding on or while you After deciding on or while you contemplate your area of contemplate your area of investigation, you should consider investigation, you should consider completing a planning table. completing a planning table.

It should easily be able to fit onto It should easily be able to fit onto one side of A4 paper – Use your one side of A4 paper – Use your logbook!logbook!

PLANNING TABLEPLANNING TABLEMake note of the variables - these are Make note of the variables - these are

things that things that couldcould change while you change while you carry out your experiment.carry out your experiment.

VARIABLESVARIABLES

Some variables may turn out to have Some variables may turn out to have no effect at all on the outcome of the no effect at all on the outcome of the investigation. investigation.

Most of these are usually quite trivial Most of these are usually quite trivial and can be ignored. and can be ignored.

Sometimes, however, it is important Sometimes, however, it is important to establish that what appears to be to establish that what appears to be an important variable does not in an important variable does not in fact affect the investigation.fact affect the investigation.

VARIABLESVARIABLES

TYPES OF VARIABLESTYPES OF VARIABLES

VARIABLES - examplesVARIABLES - examples

VARIABLEVARIABLE MEASURING MEASURING DEVICEDEVICE

UNITS UNITS &SYMBOL&SYMBOL

DISTANCEDISTANCE length length breadth breadth heightheight

RulerRuler metre metre (m) (m) centimetrecentimetre

(cm) (cm) millimetre millimetre

(mm)(mm)

VARIABLES - examplesVARIABLES - examples

VARIABLEVARIABLE MEASURING MEASURING DEVICEDEVICE

UNITS UNITS &SYMBOL&SYMBOL

AREAAREA calculated calculated rectangle rectangle area = l x barea = l x b

square square metre (m2)metre (m2)

square square centimetres centimetres (cm2)(cm2)

VARIABLES - examplesVARIABLES - examples

VARIABLEVARIABLE MEASURING MEASURING DEVICEDEVICE

UNITS UNITS &SYMBOL&SYMBOL

VOLUMEVOLUME calculated calculated cube volume cube volume ==

l x b x hl x b x h

OR FOR OR FOR LIQUIDS use a LIQUIDS use a measuring measuring cylindercylinder

cubic cubic centimetres centimetres (cm3) [1cm3 = 1 ml](cm3) [1cm3 = 1 ml]

millilitres millilitres (ml) (ml)

litres (l)litres (l)

VARIABLES - examplesVARIABLES - examplesVARIABLEVARIABLE MEASURINMEASURIN

G DEVICEG DEVICEUNITS UNITS

&SYMBOL&SYMBOL

TIMETIME

RATERATE

eg.eg. speedspeed

MASSMASS

CONCENTRATIOCONCENTRATIONN

TEMPERATURETEMPERATURE

VARIABLES - examplesVARIABLES - examplesVARIABLEVARIABLE MEASURINMEASURIN

G DEVICEG DEVICEUNITS UNITS

&SYMBOL&SYMBOL

VOLTAGEVOLTAGE

CURRENTCURRENT

ACIDITY [ pH ]ACIDITY [ pH ]

LIGHT LIGHT INTENSITYINTENSITY

VARIABLEVARIABLE

For most Higher Level investigations For most Higher Level investigations there will be a choice of variables. there will be a choice of variables.

If there is not suitable Higher Level If there is not suitable Higher Level knowledge to use for a prediction knowledge to use for a prediction then choose another variable. then choose another variable.

You need to be able to produce a You need to be able to produce a good predictiongood prediction

DEPENDENT VARIABLEDEPENDENT VARIABLE

The Dependent variable is nearly The Dependent variable is nearly always a always a continuouscontinuous variable. variable.

INDEPENDENT VARIABLEINDEPENDENT VARIABLE

A A categoriccategoric variable is normally a variable is normally a poorpoor choicechoice. .

They are often the simplest variables They are often the simplest variables to investigate but it is often to investigate but it is often impossible to generate a worthwhile impossible to generate a worthwhile prediction. prediction.

In general, don't even consider a In general, don't even consider a categoric variable.categoric variable.

INDEPENDENT VARIABLEINDEPENDENT VARIABLE

A A DiscreteDiscrete variable can get top marks, variable can get top marks, although you need to double check that although you need to double check that what you think is a discrete variable is not in what you think is a discrete variable is not in fact a continuous variable. fact a continuous variable.

Supposing you were carrying out an Supposing you were carrying out an insulation experiment and decide upon the insulation experiment and decide upon the number of layers of insulation as the number of layers of insulation as the independent variable. You would not gain independent variable. You would not gain top marks. What you should do is measure top marks. What you should do is measure the total thickness of the insulation. the total thickness of the insulation. Thickness is a continuous variable and Thickness is a continuous variable and would give access to the top marks.would give access to the top marks.

INDEPENDENT VARIABLEINDEPENDENT VARIABLE

The best choice is often a The best choice is often a ContinuousContinuous variable. variable.

This allows you to put together a This allows you to put together a quantitativequantitative prediction. prediction.

COMPLEXITYCOMPLEXITY

If the investigation is too simple it If the investigation is too simple it will be impossible to gain top marks. will be impossible to gain top marks.

If it is too complex you may run out If it is too complex you may run out of time or end up with poor quality of time or end up with poor quality results.results.

TIMETIME

This is probably the most important This is probably the most important consideration. consideration.

If you do not budget carefully you will If you do not budget carefully you will run out of time. Look carefully at what run out of time. Look carefully at what is involved to set-up and carry out the is involved to set-up and carry out the experiment, including all the repeats. experiment, including all the repeats.

Estimate the total time. Is it feasible? Estimate the total time. Is it feasible? It is no good having a brilliant plan if It is no good having a brilliant plan if you only manage to collect half the you only manage to collect half the required results.required results.

RESOURCESRESOURCES

Check that all the equipment you Check that all the equipment you need is available. need is available.

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

RANGE OF THE INDEPENDENT RANGE OF THE INDEPENDENT VARIABLEVARIABLE

The range of values you decide to The range of values you decide to investigate must be sufficient to give your investigate must be sufficient to give your prediction a good test. prediction a good test.

This means as big a range as is practical This means as big a range as is practical for you to carry out. for you to carry out.

You need You need at leastat least 5 sets of data, 8 would 5 sets of data, 8 would be more realistic, more where results can be more realistic, more where results can be obtained quickly. be obtained quickly.

In general, take as many measurements In general, take as many measurements as you have time for. as you have time for.

You need enough measurements such that You need enough measurements such that there is no doubt that your graph shows a there is no doubt that your graph shows a true and accurate trend.true and accurate trend.

RANGE OF THE DEPENDENT RANGE OF THE DEPENDENT VARIABLEVARIABLE

Don't forget to check that you can Don't forget to check that you can still measure the outcome over all still measure the outcome over all the values of the independent the values of the independent variable you intend to use. variable you intend to use.

If the dependent variable goes off If the dependent variable goes off the scale you may be able to tweak the scale you may be able to tweak some of the control variables to some of the control variables to reduce it to more manageable reduce it to more manageable values.values.

REPEATINGREPEATING Readings must be repeated a suitable number of Readings must be repeated a suitable number of

times. times. There is no magic rule for how many times you There is no magic rule for how many times you

must repeat readings. must repeat readings. If repeat readings are very similar twice would be If repeat readings are very similar twice would be

enough.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 If you get two similar and the third is way off you

know something has gone wrong and you can know something has gone wrong and you can double check it to eliminate the bad result. double check it to eliminate the bad result.

If there is a big variation between results then If there is a big variation between results then you must take more repeats to get a good you must take more repeats to get a good average. average.

RANGE OF THE DEPENDENT RANGE OF THE DEPENDENT VARIABLEVARIABLE

Don't forget to check that you can Don't forget to check that you can still measure the outcome over all still measure the outcome over all the values of the independent the values of the independent variable you intend to use. variable you intend to use.

If the dependent variable goes off If the dependent variable goes off the scale you may be able to tweak the scale you may be able to tweak some of the control variables to some of the control variables to reduce it to more manageable reduce it to more manageable values.values.

At all times, you At all times, you should be recording should be recording

your ideas and your ideas and findings in your log findings in your log

book!book!