Useful Electrical SI Units

Ampere  (symbol:  A) 

The  ampere  is defined as ‘the constant current that, if maintained in two straight parallel conductors of infinite length and negligible cross-sectional area and placed one meter apart in a vacuum, would produce between them a force equal to 2 × 10–7  newtons per unit length’.

Coulomb  (symbol:  C)
The  coulomb  is defined as ‘the charge transported through any cross-section of a conductor in one second by a constant current of one ampere’.

 Volt  (symbol:  V) 
The  volt  is defined  as  ‘the potential difference between two points such that the energy used in conveying a charge of one coulomb from one point to the other is one joule’.

 Joule  (symbol:  J)
The  joule  is defined  as  ‘the work done when the point of application of a force of one newton is displaced one meter in the direction of that force’.

Ohm (symbol:  Ω) 
The  ohm  is defined  as  ‘the electrical resistance between two points of a conductor, such that when a constant potential difference of one volt is applied between those points, a current of one ampere results’.

Newton  (symbol:  N)
The  newton is defined  as  ‘the force which, when applied to a mass of one kilogram, will give it an acceleration of one meter per second per second’.

 Watt (symbol:  W)
 The  watt  is defined  as  ‘the power resulting when one joule of energy is dissipated in one second’.

 Farad  (symbol:  F)
The  farad  is defined as ‘the capacitance of a capacitor, between the plates of which there appears a difference in potential of one volt, when it is charged to 1 coulomb.

Weber* (symbol:  Wb) 
The weber is defined  as  ‘the magnetic  fl ux that, linking a circuit of one turn, produces a potential difference of one volt when it is reduced to zero at a uniform rate in one second’. (*pronounced ‘vay-ber’)

Tesla (symbol:  T) 
The  tesla  is defined  as  ‘one weber of magnetic  fl ux per square metre of circuit area’.

Henry  (symbol:  H) 
The  Henry  is defined  as  ‘the self- or mutual-inductance of a closed loop if a current of one ampere gives rise to a magnetic  flux of one weber’.