Measurements and their Errors

Measurements and their Errors


SI Base Units
☆ The base units are the set of seven units of measure from which
all other SI units can be derived.
☆ The ones you need to know are:
☆ Mass: Kilogram (kg)
☆ Length: Metre (m)
☆ Time: Second (s)
☆ Current: Amps (A)
☆ Temperature: Kelvin (K)
☆ Amount of Substance: Mole (mol)

☆ All other units can be expressed in terms of the base units.
☆ For example:
1J = 1 kgm2s-2
1V = 1 kgm2s-3A-1


Unit Prefixes
☆ Unit prefixes should be used when stating values to avoid the use
of large amounts of noughts and standard form.
☆ You need to know the following prefixes:
T, tera: 1012 m, milli: 10-3
G, giga: 109 μ, micro: 10-6
M, mega: 106 n, nano: 10-9
k, kilo: 103 p, pico: 10-12
c, centi: 10-2 f, femto: 10-15




Significant Figures
☆ Your Calculated quantities should be given to the same number of
significant figures as the value with the least number of
significant figures used in the calculation.

☆ In tables, data should be written to the same number of
significant figures. However, when crossing multiples of 10, the
same number of decimal places should be used to avoid changing
the accuracy.

☆ The number of decimal places of the logarithm of a value should
be the same as the number of significant figures as the value.
☆ For example, ln(60) should be quoted as 4.09.