Physics Notes – Measurements and Their Errors
(Topic 1)
SI Base Units
The base units are the units that all other SI units can be derived from. There are six that you need to know at
A-Level:
Kilogram (kg) – Mass
Metre (m) – Length
Second (s) – Time
Amps (A) – Current
Kelvin (K) – Temperature
Moles (mol) – Amount of a Substance
You can add prefixes to the base units for different orders of magnitude. For example: 1kg is 1000g (kilo means
1000).
All other units can be expressed in terms of the base units. For example: 1J = 1kgm 2s-2
You can add prefixes to the base units for different orders of magnitude. These are the prefixes you need to
know:
T, tera (1012)
G, giga (109)
M, mega (106)
k, kilo (103)
c, centi (10-2)
m, milli (10-3)
µ, micro (10-6)
n, nano (10-9)
p, pico (10-12)
f, femto (10-15)
Use the multipliers to convert between units.
Significant Figures
Your calculated quantities should have the same number of significant figures as the value with the least
number of significant figures in your calculation.
In tables, data should all be to the same signification figure. This changes, however, with results that are in
different multiples of ten, in which case all of the data should be to the same decimal place rather than
significant figure.
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, In(60) should be quoted as 4.09.
Experimental Key Terms
Random Error – Measurements vary due to unpredictable circumstances. They cannot be corrected only
mitigated by making more measurements and calculating a new mean.
Systematic Error – Measurements may differ from the true value by a consistent amount each time. Can be
corrected using different techniques to take measurements.
(Topic 1)
SI Base Units
The base units are the units that all other SI units can be derived from. There are six that you need to know at
A-Level:
Kilogram (kg) – Mass
Metre (m) – Length
Second (s) – Time
Amps (A) – Current
Kelvin (K) – Temperature
Moles (mol) – Amount of a Substance
You can add prefixes to the base units for different orders of magnitude. For example: 1kg is 1000g (kilo means
1000).
All other units can be expressed in terms of the base units. For example: 1J = 1kgm 2s-2
You can add prefixes to the base units for different orders of magnitude. These are the prefixes you need to
know:
T, tera (1012)
G, giga (109)
M, mega (106)
k, kilo (103)
c, centi (10-2)
m, milli (10-3)
µ, micro (10-6)
n, nano (10-9)
p, pico (10-12)
f, femto (10-15)
Use the multipliers to convert between units.
Significant Figures
Your calculated quantities should have the same number of significant figures as the value with the least
number of significant figures in your calculation.
In tables, data should all be to the same signification figure. This changes, however, with results that are in
different multiples of ten, in which case all of the data should be to the same decimal place rather than
significant figure.
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, In(60) should be quoted as 4.09.
Experimental Key Terms
Random Error – Measurements vary due to unpredictable circumstances. They cannot be corrected only
mitigated by making more measurements and calculating a new mean.
Systematic Error – Measurements may differ from the true value by a consistent amount each time. Can be
corrected using different techniques to take measurements.
