Measyurements and their Errors AQA A-level Definitions

Accuracy

A measure of how close a measurement is to the true value.

Precision

A measure of how close a measurement is to the mean value. It only gives an indication of the magnitude of random errors, not how close data is to the true value.

Random Error

Unpredictable variation between measurements that leads to a spread of values about the true value. Random error can be reduced by taking repeat measurements.

Systematic Error

Causes all readings to differ from the true value by a fixed amount. Systematic error cannot be corrected by repeat readings, instead a different technique or apparatus should be used.

Repeatable

The same experimenter can repeat a measurement using the same method and equipment and obtain the same value.

Reproducible

An experiment can be repeated by a different experimenter using a different method and different apparatus, and still obtain the same results.

Resolution

The smallest change in a quantity that causes a visible change in the reading that a measuring instrument records.

Uncertainty

The interval that a value is said to lie within, with a given level of confidence.

reduce random errors

take repeat readings

use digital data loggers/ computer to reduce human error

use appropriate equipment e.g. better resolution

reduce systematic errors

zero the balance

calibrate equipment by measuring known value

read from bottom of miniscus to reduce parallax error

reading

one value is found

measurement

difference between 2 readings is found (2 ends of a ruler)

uncertainty in reading

± half smallest division

uncertainty in measurement

± at least 1 smallest division

repeated data uncertainty

± range/2

reduce uncertainty

fix one end of the rule

measure multiple instances

adding/ subtracting data

add absolute uncertainties

multiplying/ dividing data

add percentage uncertainties

raising to a power

multiple percentage uncertainty by power

uncertainty in a gradient

(best- worst gradient)/best gradient x 100. also works best - worst y intercept

independant

variable changed

dependant

variable measured

discrete

certain values taken - scatter + bar

continuous

can take any value - line/ scatter

categoric

can be sorted into catagories - pie/bar

ordered

can be put into ordered categories e.g. high, medium, low - bar