Topic 1 - Measurements and Uncertainty

Second (s)

Second (s)

Defined by assuming a fixed numerical value of the frequency of electromagnetic radiation emitted by a caesium atom. (More precisely, it is 9,192,631,770 oscillations of a particular type of electromagnetic wave.)

Meter (m)

Defined by assuming a fixed numerical value for the speed of light in empty space. (More precisely, it is the distance traveled by light in empty space in 1/299,792,458 of a second.)

Kilogram (kg)

Defined by assuming a fixed numerical value of Planck's constant.

Mole (mol)

One mole contains exactly 6.022 140 76 x 1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol

Kelvin (K)

Defined by assuming a fixed numerical value of the Boltzmann constant kB.

Current (A)

Defined by assuming a fixed numerical value of the elementary charge e.

Candela (cd)

The candela, symbol cd, is the SI unit of luminous intensity in a given direction (you don't need to know more about this one!)

Systematic Error

An error that causes all data points to be inaccurate in a similar way. E.g. if you forget to zero a digital scale before measuring mass or if you measure length to a point that is offset from the planned point of measurement.

Random Error

Errors caused by unknown and unpredictable issues related to the experiment.

Vector

A quantity defined by both a magnitude and a direction