Measurements and Their Errors

Question 1

Accurate

Answer 1

A measurement that is obtained, using accurately-calibrated instruments correctly, is said to be accurate.

Question 2

Base units

Answer 2

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

Question 3

Error bar

Answer 3

Representation of an uncertainty on a graph.

Question 4

Error of measurement

Answer 4

Difference between a measured value and the true value. Errors can include systematic (including zero error) and random.

Question 5

Linear

Answer 5

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

Question 6

Precision of a measurement

Answer 6

Precise measurements are ones in which there is very little spread about the mean value. Precision depends only on the extent of random error and it gives no indication of how close the results are to the true value.

Question 7

Precision of an instrument

Answer 7

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

Question 8

Probable Error

Answer 8

Estimate of the uncertainty of a measurement

Question 9

Random error

Answer 9

Error of measurement due to results varying in an unpredictable way from one measurement to the next. They 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 10

Range of a set of a reading

Answer 10

The range of a set of readings of the same measurement is the difference between the minimum and the maximum reading.

Question 11

Range of an instrument

Answer 11

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

Question 12

Sensitivity of an instrument

Answer 12

The output reading per unit input quantity.

Question 13

SI System

Answer 13

The scientific system of units.

Question 14

Systematic errors

Answer 14

Causes readings the differ from the true value by a consistent amount each time a measurement is made. Sources of systematic errors can include the environment, methods of observation or instruments used.

Question 15

Uncertainty

Answer 15

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

Question 16

Zero error

Answer 16

Any indication that a measuring system gives a false reading when the true value of a measured quantity is zero. A zero error may result in a systematic uncertainty.