practicaldef1

Question 1

Accuracy.

Answer 1

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

Question 2

Calibration.

Answer 2

Marking a scale on a measuring instrument.
This involves establishing the relationship between indications of a measuring instrument and standard or reference quantity values, which must be applied.

Question 3

Data.

Answer 3

Information, either qualitative or quantitative, that has been collected.

Question 4

Measurement error.

Answer 4

The difference between a measured value and the true value.

Question 5

Anomalies.

Answer 5

These are values in a set of results which are judged not to be part of the variation caused by random uncertainty.

Question 6

Random errors.

Answer 6

These cause readings to be spread about the true value, due to results varying in an unpredictable way from one measurement to the next.

Random errors are present when any measurement is made, and cannot be corrected.

The effect of random errors can be reduced by making more measurements and calculating a new mean

Question 7

Systematic uncertainty.

Answer 7

These cause readings to differ from the true value by a consistent amount each time a measurement is made.

Sources of systematic error can include the environment, methods of observation or instruments used.

Systematic errors cannot be dealt with by simple repeats. If a systematic error is suspected, the data collection should be repeated using a different technique or a different set of equipment, and the results compared.

Question 8

Zero error.

Answer 8

Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero, eg the needle on an ammeter failing to return to zero when no current flows.

A zero error may result in a systematic uncertainty.

Question 9

Fair test.

Answer 9

A fair test is one in which only the independent variable has been allowed to affect the dependent variable.

Question 10

Hypothesis.

Answer 10

A proposal intended to explain certain facts or observations.

Question 11

Intervals.

Answer 11

The quantity between readings.

Question 12

Precision.

Answer 12

Precise measurements are ones in which there is very little spread about the mean value.

Precision depends only on the extent of random errors - it gives no indication of how close results are to the true value.

Question 13

Range.

Answer 13

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

Question 14

Repeatable.

Answer 14

A measurement is repeatable if the original experimenter repeats the investigation using same method and equipment and obtains the same results

Question 15

Reproducible.

Answer 15

A measurement is reproducible if the investigation is repeated by another person, or by using different equipment or techniques, and the same results are obtained.

Question 16

Resolution.

Answer 16

This is the smallest change in the quantity being measured (input) of a measuring instrument that gives a perceptible change in the reading.

Question 17

Sketch graph.

Answer 17

A line graph, not necessarily on a grid, that shows the general shape of the relationship between two variables. It will not have any points plotted and although the axes should be labelled they may not be scaled.

Question 18

True value.

Answer 18

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

Question 19

Uncertainty.

Answer 19

The interval within which the true value can be expected to lie, with a given level of confidence or probability.

Question 20

Vailidity.

Answer 20

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

For example, an investigation to find out if the rate of a chemical reaction depended upon the concentration of one of the reactants would not be a valid procedure if the temperature of the reactants was not controlled

Question 21

Valid conclusion.

Answer 21

A conclusion supported by valid data, obtained from an appropriate experimental design and based on sound reasoning.

Question 22

Categoric variables.

Answer 22

Categoric variables have values that are labels eg names of plants or types of material or reading at week 1, reading at week 2 etc.

Question 23

Continuous variables.

Answer 23

Continuous variables can have values (called a quantity) that can be given a magnitude either by counting (as in the case of the number of shrimp) or by measurement (eg light intensity, flow rate etc).

Question 24

Control variables.

Answer 24

A control variable is one which may, in addition to the independent variable, affect the outcome of the investigation and therefore has to be kept constant or at least monitored.

Question 25

Dependent variables.

Answer 25

The dependent variable is the variable of which the value is measured for each and every change in the independent variable.

Question 26

Independent variables.

Answer 26

The independent variable is the variable for which values are changed or selected by the investigator.

Question 27

Nominal variables.

Answer 27

A nominal variable is a type of categoric variable where there is no ordering of categories (eg red flowers, pink flowers, blue flowers)