Science practical key terms

Hazard A chemical or piece of apparatus that could cause harm.

Risk An action that could result in the hazard causing harm – the dangerous part of

the method

Control measures Something that can be done to reduce or prevent a risk while allowing you to

carry out the experiment.

variable The variable that you change

Dependent variable The variable that you measure and record during the investigation – the results

Controlled variable A variable that should be kept the same because it may affect the investigation

Range The maximum and minimum values of the independent or dependent variables.

This should not be too big or too small.

Accuracy A result is considered accurate if it is judged to be close to the true value.

Anomaly/Anomalou

s

Value in a set of results which does not fit with the other results.

Reliability For the data to be reliable, the repeat results must be close together

Repeatable Results are repeatable if the experiment is carried out by a single student/group

and the repeat results are close together.

Reproducible Results are reproducible, if repeats by different students/ groups obtains the

same or similar results. This could include using different equipment/ methods.

This is a harder test of the quality of data than repeatability

Resolution This is the smallest change in the quantity being measured by a measuring

instrument that can be observed. For example, 1mm on a

1 metre ruler, 1°C on a thermometer., 0.01s on a stopwatch.

Valid conclusion A conclusion supported by valid data, obtained from an appropriate

experimental design and based on sound reasoning.

Validity of

experimental design

Suitability of the investigative procedure to answer the question being asked.

Strategies to ensure validity include fair tests and controls that aim to isolate

the effect of the independent variable on the dependent variables.

Was it a good experiment?

Measurement

error

The difference between a measured value and the true value. – More Accurate

equipment could be used

Precision

This shows the closeness of agreement between measured values – if the

repeat results are all close together then they are precise.

It gives no indication of how close results are to the true value – the result may

be precise but not accurate!

Random error

These occur due to results varying in an unpredictable way from one

measurement to the next.

The effect of random errors can be reduced by taking more measurements and

calculating a mean.

Systematic error

These cause readings to differ from the true value by a consistent amount each

time a measurement is made.

Systematic errors can include the influence of the environment, the methods of

observation or the instruments used.

The effect of systematic errors cannot be reduced by increased repeats.

True value This is the value that would be obtained in an ideal measurement.

Uncertainty

The interval within which the true value can be expected to lie, with a given

level of confidence or probability, eg “the temperature is 20 °C ± 2 °C, at a level

of confidence of 95 %.