Electrical Units


For the quick reference the basic electrical quantity's unit and their symbol is listed below. 

Capacitance C Farad F
Charge Q Coulomb C
Conductance G Siemens S
Current I Ampere A
Energy W Joule J
Frequency f Hertz Hz
Impedence Z Ohm Ω
Inductance L Henry H
Power P Watt W
Reactance X Ohm Ω
Resistance R Ohm Ω
Voltage V Volt V

The Basic Electrical Quantities and Their Units

Potential Difference:
It is defined as the difference of electric potential between the two points in an electric circuit. 
Its symbol is V and the unit of measurement is volts.
The instrument used to measure the potential difference is called as Voltmeter. The voltmeter is always connected in parallel with the circuit whose voltage is to be calculated.

Electric Current:
The flow of electrons in one direction along any path or around any circuit is called Electric current.
Its Symbol is I and its unit is Ampere (A)
The current in a circuit is measured by the instrument known as Ammeter. Ammeter is always connected in series with the circuit.

The property of a conductor which opposes the flow of electric current through it is known as resistance of that conductor.
Its symbol is R, and its unit is Ohm
The instrument that measures resistance is known as ohmmeter.

Electrical Power:
The rate at which work is done in an electic circuit is called electric power.
Power = Voltage x current
P = V.I
The basic unit of electric power is watt. It is measured by the instrument known as wattmeter.

Electrical Energy:
The total amount of work done in an electric circuit is called as electric energy.
Energy = Power x time
W = Pt
W = VIt
The basic unit of electic energy is Joule or watt-sec. The Joule or watt-sec is a very small unit. In practice, for the measurement of electrical energy watt-hour or Kilo watt-hour(Kwh) are used. 
The instrument used to measure the electrical energy consumed is Energy meter.


Flux density   B Tesla   T
Magnetic flux   Φ Weber   Wb
Magnetizing force   H Ampere-turns/meter   At/m
Magnetomotive force   Fm Ampere-turn   At
Permeability   µ Webers/ampere-turns-meter   Wb/Atm
Reluctance   R Ampere-turns/weber   At/Wb

Magnetic Flux:
The total number of magnetic lines of force in a magnetic field is called magnetic flux. It is represented by greek letter Φ.

Magnetic Flux Desnsity:
The magnetic flux density at any point is the magnetic flux passing per unit area at that point.

The ability of a material to conduct magnetic flux through it, is known as the permeability of that material.

Relative Permeability:
The ratio of the permeability of material to the permeability of air or vaccum is known as relative permeability of the material.

Magnetic Field Intensity:
Field intensity at a point due to a magnetic field is the force acting on a unit n-pole placed at that point.

Magneto - Motive Force (MMF):
Teh force which drives the magnetic flux through a magnetic circuit is called the magneto motive force. It is produced by passing electric current through a wire of number of turns. It is measured in Ampere Turns (AT)
Ampere Turns (AT): It is the product of number of turns and the current flowing through these turns.
MMF = No. of turns x Current

Magnetic Flux:
The total magnetic lines of force passing through the material is called magnetic flux. The unit of magnetic flux is weber.

It is the property of a magnetic circuit which opposes the establishment of megnetic flux in it. The unit of reluctance is ampere turns per weber (AT)/(Wb)