# Unit of Voltage

## What is Unit of Voltage - SI Unit of Voltage

Voltage can be defined as the electric potential between two points. In a conductor, if the electric field is uniform, the potential difference between the points is,

V = EL

By using various equations of resistivity, current, and resistance, another equation can be derived,

V = EL
V = JL
V = (I/A)L
V = I ( L/A)
V = IR

From the above equation, we can deduce that the voltage or the potential difference across the resistor can be found by multiplying the current with the resistance. The unit of potential difference is Volt (V) which is also equal to Joule per Coulomb (J/C).

SI Unit of Voltage

The SI unit for voltage is Volt and is represented by the letter v. volt is a derived SI unit of electromotive force or electric potential. Thus, due to this volt can be defined in a number of ways.

Volt can be defined as ‘the electric potential present along with a wire when an electric current of one ampere dissipates the power of 1 watt (W).

V = W/A
Also, volt can be expressed as the potential difference that exists between two points in an electric circuit which imparts an energy of 1 joule (J) per coulomb of charge that flows through the circuit.

V = potential energy/ charge
V = J/ C = Kg m2/ A s3

It can also be expressed as ampere times ohm, joule per coulomb or watt per ampere.\
V = AΩ = W/A (energy per unit charge) = J/C (power per unit current)
It can also be expressed as it is given in its SI unit,
1 V = 1 kg m2s -3 A -1 (One kilogram meter squared per second cubed per ampere)

Below are some other electrical units,

 Electrical parameter SI unit Symbol Charge Coulomb Q Impedance Ohm Z Conductance Simen G or ひ Capacitance Farad C Inductance Henry L or H Voltage Volt V or E Power Watts W Frequency Hertz Hz Resistance Ohm R or Ω

Voltage source

A voltage source is basically a device which is used in electric circuits having fixed potential difference at both the ends. The voltage source can be a battery or any other source which has fixed potential difference and direct current. In the circuit diagrams, the voltage source is depicted as shown in the figure below.

In case the ends of the voltage source are connected to a circuit which has multiple numbers of resistors, voltmeters, etc then a complete circuit is formed and the current can now flow from one end to the other. And if the current is flowing, then it is the same on both the terminals of the voltage source.

A voltage source is a part of a complete circuit which can produce an electromotive force. Electromotive force is represented using the symbol ε. The unit of electromotive force is the same as voltage, that is it is volt. Here volt is equal to a joule per coulomb (J/C). In case of an ideal source, the electromotive force is equal to the voltage difference,

ε = V = IR

Real sources such as batteries are not considered as ideal sources as they have some source of internal resistance. If r denotes the internal resistance of a battery, then the voltage difference present across the battery is,

V = ε -Ir

This can also be called as the terminal voltage of the battery. When a complete circuit is made using a resistor which has resistance R, then the current flowing through can be found using the equation,

V =IR
IR = ε -Ir
IR + Ir = ε
I (R +r) = ε
I = (R + r)/ ε

Thus, the current is equal to the electromotive force of the source divided by the total resistance present in the circuit.