Definitions of SI Units

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.

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