Measurements & their errors

Question 1

accepted value

Answer 1

value of the most accurate measurement available, sometime referred to as the ‘true value’

Question 2

accuracy

Answer 2

The closeness of a measurement to the true value (if known)

Question 3

Base units

Answer 3

The units that define the SI system (e.g. the metre, the kilogram, the second, the ampere).

Question 4

dependent variable

Answer 4

a physical quantity whose value depends on the value of another physical variable

Question 5

differentiation

Answer 5

mathematical process of finding the gradient of a line from its equation.

Question 6

error bar

Answer 6

representation of an uncertainty on a graph

Question 7

independent variable

Answer 7

physical quantities whose values are selected or controlled by the experimenter

Question 8

Integration

Answer 8

Mathematical process of finding the area under the curve from its mathematical equation

Question 9

Limit of proportionality

Answer 9

The limits beyond which when a wire or a spring is stretched its extension is no longer proportional to the force that stretches it

Question 10

linear

Answer 10

two quantities are said to have a linear relationship if the change of one quantity is proportional to the change of the other

Question 11

linearity

Answer 11

an instrument that gives readings that are directly proportional to the magnitude of the quantity being measured

Question 12

logarithmic scale

Answer 12

a scale such that equal intervals correspond to a change by a constant factor

Question 13

mean value of a set of readings

Answer 13

sum of the readings divided by the number of readings

Question 14

percentage uncertainty

Answer 14

=uncertainty/mean value x 100%

Question 15

precision of a measurement

Answer 15

the degree of exactness of a measurement, usually expressed as the uncertainty of the readings used to obtain the measurement

Question 16

precision of an instrument

Answer 16

the smallest non-zero reading that can be measured using the instrument, also sometimes referred to as the instrument sensitivity or resolution

Question 17

random errors

Answer 17

errors vary randomly with no recognisable pattern or trend or bias

Question 18

range of a set of readings

Answer 18

the difference between the largest and smallest reading

Question 19

range of an instrument

Answer 19

the difference between the minimum and maximum reading that can be obtained using the instrument

Question 20

reliability

Answer 20

an experiment or measurement is reliable if a consistent value is obtained each time it is repeated under identical conditions. The reliability of an experiment is increased if random and systematic errors have been considered and eliminated and, where appropriate, a more precise best fit line has been obtained.

Question 21

repeatable

Answer 21

an experiment or measurement that gives the same results when it is repeated by the original experimenter using the same method and equipment

Question 22

reproducable

Answer 22

an experiment or measurement that gives the same results when it is repeated by another person or by using different equipment or techniques.

Question 23

sensitivity of an instrument

Answer 23

output response per unit input quantity

Question 24

SI system

Answer 24

scientific system of units

Question 25

systematic errors

Answer 25

differ systematically and show a pattern or trend or bias

Question 26

uncertainty of a measurement

Answer 26

half the range of the readings used to obtain the measurement

Question 27

valid measurement

Answer 27

measurements that give the required information by an acceptable method

Question 28

zero error of an instrument

Answer 28

a systematic error due to a non-zero reading when the quantity to be measured is zero