# Definitions of SI Units

**meter (m) **The *meter *is the length equal to the distance traveled

by light, in vacuum, in a time of 1>299,792,458 second.

**kilogram (kg) **The *kilogram *is the unit of mass; it is defined

by taking the value of Planck’s constant *h *to be exactly

6.62607015 * 10-34 kg # m2>s.

**second (s) **The *second *is the duration of 9,192,631,770

periods of the radiation corresponding to the transition

between the two hyperfine levels of the ground state of the

cesium-133 atom.

**ampere (A) **The *ampere *is a current of one coloumb per second,

where the coulomb is defined in terms of the elementary

charge *e*.

**kelvin (K) **The *kelvin, *unit of thermodynamic temperature,

is defined by taking the value of the Boltzmann constant *k *to be

exactly 1.380649 * 10-23 J>K.

**ohm **(_) The *ohm *is the electric resistance between two

points of a conductor when a constant difference of potential

of 1 volt, applied between these two points, produces in this

conductor a current of 1 ampere, this conductor not being the

source of any electromotive force.

**coulomb (C) **The *coulomb *is the quantity of electricity such

that the elementary charge e is exactly 1.602176634 * 10-19 C

transported in 1 second by a current of 1 ampere.

**candela (cd) **The *candela *is the luminous intensity, in a

given direction, of a source that emits monochromatic radiation

of frequency 540 * 1012 hertz and that has a radiant intensity

in that direction of 1>683 watt per steradian.

**mole (mol) **The *mole *is the SI unit of substance. One mole

contains exactly 6.02214076 * 1023 elementary entities.

**newton (N) **The *newton *is that force that gives to a mass of

1 kilogram an acceleration of 1 meter per second per second.

**joule (J) **The *joule *is the work done when the point of application

of a constant force of 1 newton is displaced a distance of 1 meter

in the direction of the force.

**watt (W) **The *watt *is the power that gives rise to the production

of energy at the rate of 1 joule per second.

**volt (V) **The *volt *is the difference of electric potential between

two points of a conducting wire carrying a constant current of

1 ampere, when the power dissipated between these points is

equal to 1 watt.

**weber (Wb) **The *weber *is the magnetic flux that, linking

a circuit of one turn, produces in it an electromotive force of

1 volt as it is reduced to zero at a uniform rate in 1 second.

**lumen (lm) **The *lumen *is the luminous flux emitted in a solid

angle of 1 steradian by a uniform point source having an intensity

of 1 candela.

**farad (F) **The *farad *is the capacitance of a capacitor between

the plates of which there appears a difference of potential of

1 volt when it is charged by a quantity of electricity equal to

1 coulomb.

**henry (H) **The *henry *is the inductance of a closed circuit in

which an electromotive force of 1 volt is produced when the

electric current in the circuit varies uniformly at a rate of 1 ampere

per second.

**radian (rad) **The *radian *is the plane angle between two radii

of a circle that cut off on the circumference an arc equal in

length to the radius.

**steradian (sr) **The *steradian *is the solid angle that, having its

vertex in the center of a sphere, 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.