Gcse 'isa' Key Terms

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Accuracy

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An accurate measurement is one which is close to the true value

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Anomalous

Back 2

If you have a set of measurements (data) from an experiment and one of the results does not fit the pattern obtained then this result is anomalous (it is an anomaly)

Front 3

Calibration

Back 3

This involves fixing known points and then marking a scale on a measuring instrument between these fixed points

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Data

Back 4

This refers to a collection of measurements

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Datum

Back 5

This is the singular of data

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Errors: Random

Back 6

These cause readings to be different from the true value. Random errors may be detected and compensated for by taking a large number of readings. Random errors may be caused by human error, a faulty technique in taking the measurements or by faulty equipment

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Errors: Systematic

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These cause readings to be spread out about some value other than the true value. Using an incorrectly calibrated instrument will lead to systematic errors

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Errors: Zero

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These are caused by measuring instruments that have a false zero. For example: A zero error will occur if an electronic balance indicates a value other than zero when no mass is placed on the pan. A zero error is a type of systematic error

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Evidence

Back 9

This comprises data which have been subjected to some form of validation. It is possible to give a measure of importance to data which has been validated when coming to an overall judgement

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Fair Test

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A fair test is one in which only the independent variable has been allowed to affect the dependent variable. A fair test can usually be achieved by keeping all variables other than the independent variable constant

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Precision

Back 11

The precision of an instrument is determined by the limits of the scale on the instrument being used. Precision is related to the smallest scale division on the measuring instrument that you are using. Using a ruler with a millimetre scale on it to measure the thickness of a book will give greater precision than using a ruler that is only marked in centimetres.

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Range

Back 12

The range of a set of measurements states the maximum and minimum values

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Reliability

Back 13

The results of an investigation may be considered reliable if the results can be repeated. If someone else can carry out your investigation adn get the same results then your results are more likely to be reliable. One way of checking reliability is to compare your results with those of others. The reliability of results can be improved by carrying out repeat measurements.

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Tolerance

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This is the acceptable range either side of the intended value. For example, if you order a set of 100 gram masses with a tolerance limit of 1 gram, then you will accept any value of mass from 99 grams to 101 grams

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True Value

Back 15

This is the accurate value which would be found if the quantity could be measured without any errors

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Validity

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Data is only valid for use in coming to a conclusion if the measurements taken are affected by a single independent variable only

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Variables: Categoric

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A categoric variable has values which are described by laves. For example, if you investigate the effect of acid on different metals, the type of metal used is a categoric variable. When you present the results of an investigation of this type you must use a bar chart or pie chart and not a line graph to illustrate your results

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Variables: Continuous

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A continuous variable is one which can have any numerical value. For example, if you investigate how the height form which a ball is released above the floor affects the speed at which the ball hits the floor you are using a continuous variable since it could be any height that you choose. The results of an investigation of this type should be presented on a line graph.

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Variable: Control

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A control variable is one which may, in addition to the independent variable, affect the outcome of an investigation. This means that you should keep these variables constant otherwise it may not be a fair test. If it is not possible to keep it constant you should monitor it to see if any change leads to an effect on the outcome of the experiment

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Variable: Dependent

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The dependent variable is the variable the value of which you measure for each change in the independent variable. It is the thing that changes as a result of you changing something else

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Variable: Independent

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The independent variable is the variable for which values are changed or selected by the investigator. It is the only thing that you deliberately change to see what effect it has. The independent variable can be thought of as being the cause and the dependent variable can be thought of as being the event

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Variable: Discrete

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This is a type of categoric variable whose values are restricted to whole numbers. For example: The number of pupils in a form group

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Variable: Ordered

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This is a type of categoric variable that can be ranked. For example: The size of marble chips could be described as large, medium or small