Physical Quantities, Units and Measurements

7 base units

mass, length, time, temperature, electrical current, amount of substance, luminous intensity

unit and symbol for mass

kilogram, kg

unit and symbol for length

metre, m

unit and symbol for time

second, s

unit and symbol for temperature

kelvin, K

unit and symbol for electrical current

ampere, A

unit and symbol for amount of substance

mole, mol

unit and symbol for luminous intensity

candela, cd

pico- abbreviation and form

p/10^-12

nano- abbreviation and form

n/10^-9

micro- abbreviation and form

µ/10^-6

milli- abbreviation and form

m/10^-3

centi- abbreviation and form

c/10^-2

deci- abbreviation and form

d/10^-1

kilo- abbreviation and form

k/10^3

mega- abbreviation and form

M/10^3

giga- abbreviation and form

G/10^9

tera- abbreviation and form

T/10^12

random error definition

an error that is unpredictable within the experiment

systematic error definition

an error that does not happen by chance but instead is introduced by an inaccuracy in the apparatus or its use

zero error definition

caused when an instrument is not properly calibrated or adjusted and therefore it gives a non-zero value

precision definition

the degree to which repeated values, collected under the same conditions in an experiment show the same results

accuracy definition

degree to which a value obtained by an experiment is close to the true value

absolute uncertainty definition

shows how large the uncertainty actually is

percentage uncertainty definition

the absolute uncertainty divided by the measured value expressed as a percentage

percentage uncertainty equation

(uncertainty/measured value) x 100%

for a compound quantity in the form y = ab rule is:

% uncertainty in y = % uncertainty in a + % uncertainty in b

for a compound quantity in the form y = a/b rule is:

% uncertainty in y = % uncertainty in a + % uncertainty in b

for a compound quantity in the form y = a² rule is:

% uncertainty in y = 2 x % uncertainty in a

for a compound quantity in the form y = aⁿ rule is:

% uncertainty in y = n x % uncertainty in a