National Measurement Regulations 1999

2.1

frequency

hertz

Hz

The frequency of a regularly recurrent phenomenon that repeats itself once each second.

2.2

force

newton

N

The force that, when applied to a body having a mass of 1 kilogram, causes an acceleration of 1 metre per second squared in the direction of the application of the force.

2.3

pressure

pascal

Pa

The pressure resulting from a force of 1 newton applied uniformly over an area of 1 square metre.

2.4

energy, work

joule

J

The work done or the energy expended when a force of 1 newton moves the point of application 1 metre in the direction of that force.

2.5

power, including sound power

watt

W

The power used when work is done or energy is expended at the rate of 1 joule per second.

2.6

electric charge

coulomb

C

The quantity of electric charge that is transferred each second by an electric current of 1 ampere.

2.7

potential difference, electro‑motive force

volt

V

The potential difference that exists between 2 points on a conductor carrying an unvarying electric current of 1 ampere when the power dissipated between those points is equal to 1 watt.

2.8

electric capacitance

farad

F

The electric capacitance that exists between 2 conductors when the transfer of an electric charge of 1 coulomb from one to the other changes the potential difference between them by 1 volt.

2.9

electric conductance

siemens

S

The electric conductance of a conductor that has an electric resistance of 1 ohm.

2.10

electric inductance

henry

H

The electric inductance of a closed circuit in which an electromotive force of 1 volt is produced when the electric current that traverses the circuit varies uniformly at the rate of 1 ampere per second.

2.11

electric resistance

ohm

Ω

The electric resistance between 2 points on a conductor that does not contain any source of electromotive force when a constant potential difference of 1 volt maintained between those points results in a current of 1 ampere in the conductor.

2.12

magnetic flux

weber

Wb

The magnetic flux that, linking a circuit of 1 turn, produces in that circuit an electromotive force of 1 volt if the magnetic flux is reduced to zero at a uniform rate in 1 second.

2.13

magnetic flux density

tesla

T

The magnetic flux density that results if a magnetic flux of 1 weber is uniformly distributed over a plane 1 square metre in area, the direction of the magnetic flux density being perpendicular to that plane.

2.14

luminous flux

lumen

lm

The luminous flux emitted into a solid angle of 1 steradian by an isotropic point source having a luminous intensity of 1 candela.

2.15

illuminance

lux

lx

The illuminance produced at the surface of a sphere having a radius of 1 metre by a point source that:

(a) is situated at its centre; and

(b) has a luminous intensity of 1 candela in all directions.

2.16

activity of a radionuclide

becquerel

Bq

The activity of a radionuclide that is undergoing 1 transformation per second on average.

2.17

absorbed dose, absorbed dose index, kerma, specific energy imparted

gray

Gy

The absorbed dose, absorbed dose index, kerma or specific energy imparted when 1 joule is imparted to 1 kilogram of irradiated matter

2.18

dose equivalent

sievert

Sv

The sievert is the dose equivalent or dose equivalent index where:

(a) an absorbed dose of ionising radiation equal to 1 gray is delivered to a biological material; and

(b) the conditions under which the dose is delivered satisfy the formula:

Q × N = 1

where:

Q is a factor that is the quality factor representing the effect on the detriment of the microscopic distribution of absorbed energy; and

N is a factor that is the product of all other modifying factors specified by the International Commission on Radiological Protection as at the commencement of these regulations.

2.19

plane angle

radian

rad

The radian is the plane angle between 2 radii of a circle that cut off on the circumference an arc equal in length to the radius.

2.20

solid angle

steradian

sr

The steradian is the solid angle that has its vertex in the centre of a sphere and cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere.

2.21

catalytic activity

katal

kat

The katal is a unit of catalytic activity equal to 1 mole per second.