Experiment Key Words

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 measuring instrument
• This involves establishing the relationship between indication of a measuring instrument and standard or reference quantity values, which must be applied e.g. placing a thermometer in melting ice to see wether it reads 0 degrees Celsius, in order to check if it has been calibrated correctly

Question 3

Data

Answer 3

Information, either qualitative or quantitative, that have 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 raised by random uncertainty

Question 6

Random Error

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 y making more measurements and calculating a new mean

Question 7

Systematic Error

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 instruments used
• Systematic error 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 e.g. the needle on an ammeter failing to return to zero when no current flows
• A zero error may result tin a systematic uncertainty

Question 9

Evidence

Answer 9

Data that has shown to be valid

Question 10

Fair Test

Answer 10

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

Question 11

Hypothesis

Answer 11

A proposal intended to explain certain facts or observations

Question 12

Interval

Answer 12

The quantity between readings e.g. a set of 11 readings equally spaced over a distance of 1 metre would give an interval of 10 centimetres

Question 13

Precision

Answer 13

• 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 14

Prediction

Answer 14

A predication is a statement suggesting what will happen in the future, based on observation, experience or a hypothesis

Question 15

Range

Answer 15

• The maximum and minimum values of the independent or dependent variables
• For example a range of distances may be quotes as either; ‘From 10cm to 50 cm’ or ‘From 50cm to 10cm’

Question 16

Repeatable

Answer 16

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

Question 17

Reproducible

Answer 17

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

Question 18

Resolution

Answer 18

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

Question 19

Sketch graph

Answer 19

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 20

True Value

Answer 20

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

Question 21

Uncertainty

Answer 21

The interval within which the true value ca be expected to lie, with a given level of confidence o rporbeility e.g. “the temperature is 20 degrees Celsius plus minus 2 degrees Celsius, at a level of confidence of 95%”

Question 22

Validity

Answer 22

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 23

Valid conclusion

Answer 23

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

Question 24

Variables

Answer 24

These are physical, chemical or biological quantities or characteristics

Question 25

Categoric Variables

Answer 25

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

Question 26

Continuous Variables

Answer 26

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 bu measurement (e.g. light intensity, flow rate etc.)

Question 27

Control Variables

Answer 27

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 28

Dependent Variables

Answer 28

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

Question 29

Independent Variables

Answer 29

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

Question 30

Nominal Variables

Answer 30

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

Question 31

Random error, what are some reasons?

Answer 31

An error that affects a measurement in an unpredictable fashion

• Observer error (writing down a measurement wrong
• The readability of the equipment (e.g. trying to measure the height to which a bouncy ball rises, or reading an ammeter when the current is changing quickly
• External factors in the measured item (e.g. changes in ambient temperature or pressure in gas measurements)

Question 32

What are some reasons for systematic error?

Answer 32

1. Poor technique (e.g. not avoiding parallax when reading an analogue voltmeter)
2. Zero error on an instrument (e.g. a newton-meter that shows a value for force when there is nothing hanging from it)
3. Poor calibration of the instrument (the scale on a thermometer being incorrect so that one degree is too large)
4. The wrong unit being recorded

Question 33

How can a systematic error be reduced?

Answer 33

-Will NOT be reduced by repeating measurements
-Use different methods or instruments to obtain the same value will allow you to compare he results obtained and may identify a systematic error
E.G temperature with mercury thermometer, infrared camera, bimetallic strip thermometer would allow a comparison to be made between instruments

Question 34

What is parallax?

Answer 34

Occurs when the position of an object appears to be different when viewed from different positions. This can lead to measurement errors. A mirror is often placed behind the pointer of metres so that by lining up the pointer and its image you know you are avoiding parallax

Question 35

How can you take into account systematic errors?

Answer 35

1. Correcting the value of the readings taken
   E.G if a newton meter has a systematic error of +0.2N then we can subtract this from our results to obtain a more accurate value

Question 36

What is the sensitivity of an instrument?

Answer 36

A sensitive instrument produces a large change in output for a small change in input E.G a sensitive analogue ammeter is one that shows a large deflection for a small change in current

Question 37

What is the resolution of a measuring instrument?

Answer 37

Resolution is the smallest observable change being measured by a measuring instrument
E.G measuring diameter of metal bar that is about 3mm in diameter, could use a ruler that can measure to the nearest 0.5mm or they could use a micrometer such can measure tot he nearest 0.005mm and the micrometer will give a more accurate measurement with greater resolution