Uncertainty 2

Question 1

Percentage uncertainty of measurement =

Answer 1

(uncertainty )/value x 100%

Question 2

Percentage uncertainty of repeated measurement

Answer 2

(uncertainty )/(mean value) x 100%

Question 3

size of real object =

Answer 3

size of real object= (size of image)/magnification

Question 4

Uncertainty =

Answer 4

half the range +/- mean value

Question 5

Percentage uncertainty of graph

Answer 5

percentage uncertainty= |best gradient (gradient of line of best fit)-worst gradient (steepest/shallowest gradient of line of best fit)|/(best gradient) × 100%

Question 6

Percentage uncertainty of y-intercept

Answer 6

percentage uncertainty= |best y intercept-worst y intercept|/(best y intercept) × 100%

Question 7

Uncertainty of ruler

Answer 7

When measuring length, two uncertainties must be included: the uncertainty of the placement of the zero of the ruler and the uncertainty of the point the measurement is taken from. As both ends of the ruler have a ±0.5 scale division uncertainty, the measurement will have an uncertainty of ±1 division. For most rulers, this will mean that the uncertainty in a measurement of length will be ±1 mm.

Question 8

Uncertainty from sig figs

Answer 8

one unit of lowest decimal place e.g. if value is 123.456

then uncertainty is +/- 0.001

Question 9

Temperature is measured in

Answer 9

Kelvin

Question 10

1W =

Answer 10

1 J/s

Question 11

Micrometers give readings to within (What is the precision)

Answer 11

0.01mm

Question 12

A digital micrometer gives a read-out equal to the

Answer 12

width of the micrometer gap

Question 13

How do micrometers work

Answer 13

An analogue micrometer has a barrel on a screw thread with a pitch of 0.5mm – the edge of the barrel is marked in 50 equal intervals so each interval corresponds to changing the gap of the micrometer by 0.5/50mm = 0.01mm – the stem of the micrometer is marked with a linear scale graduated in 0.5mm marks – the reading of a micrometer is where the linear scale intersects the scale on the barrel. The linear scale + (barrel scale * 0.01)

Question 14

How do vernier callipers

Answer 14

Vernier callipers are used for measurements of distances up to 100mm or more. Readings can be made to within 0.1mm. The sliding scale of an analogue vernier has ten equal intervals covering a distance of exactly 9mm so each interval of this scale is 0.1mm less than a 1mm interval. To make a reading – the zero mark on the sliding scale is used to read the main scale to the nearest millimetre. The reading is rounded down to the nearest millimetre. The mark on the sliding scale closest to a mark on the millimetre scale is located and its number noted. Multiplying this number by 0.1mm gives the distance to be added on the rounded-down reading

Question 15

Accuracy

Answer 15

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

Question 16

Calibration

Answer 16

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 17

Data

Answer 17

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

Question 18

Measurement error

Answer 18

The difference between a measured value and the true value.

Question 19

Anomalies

Answer 19

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

Question 20

Random error

Answer 20

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 21

Systematic error

Answer 21

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 22

Zero error

Answer 22

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 23

Evidence

Answer 23

Data that have been shown to be valid.

Question 24

Fair test

Answer 24

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

Question 25

Hypothesis

Answer 25

A proposal intended to explain certain facts or observations.

Question 26

Interval

Answer 26

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

Question 27

Precision

Answer 27

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 28

Prediciton

Answer 28

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

Question 29

Range

Answer 29

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

Question 30

Repeatable

Answer 30

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

Question 31

Reproducible

Answer 31

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 32

Resolution

Answer 32

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

Question 33

Sketch graph

Answer 33

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 34

True value

Answer 34

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

Question 35

Uncertainty

Answer 35

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 %”.

Question 36

Validity

Answer 36

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 37

Valid conclusion

Answer 37

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

Question 38

Categoric variables

Answer 38

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 39

Continuous variables

Answer 39

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 40

Control variables

Answer 40

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 41

Dependent variables

Answer 41

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

Question 42

Independent variables

Answer 42

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

Question 43

Nominal variables

Answer 43

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

Question 44

Variables

Answer 44

These are physical, chemical or biological quantities or characteristics.