What is Voltage? Definition, Formula and Unit

What is Voltage?

Definition: Voltage (also known as the potential difference, electromotive force, electric pressure, or electric tension) is the difference in electric potential between two points for which it pushes current around the circuit. 

If you are a little bit confused by the definition, then let's look at the hydraulic or heat analogy to understand it better -

What is Voltage? Definition, Formula and Unit

hydraulic analogy: If we connect two tanks with the same water level by a pipe, we see that there is no water flow. But if we take two tanks with different water levels, we see that water flows from the higher water level to the lower one. 

The difference in water level makes water pressure for which the water flows from one tank to other. If we continue these analogies we see the current is similar to water flow, where water pressure indicates the voltage or electrical potential difference.

Heat analogy: Again from heat analogy we see - if there is a temperature difference between two objects connected by a thermal conductor, heat flows from the object of higher temperature to the object of lower temperature. 

Here the temperature difference makes the heat flow from the hotter object to the cooler one. If we continue these analogies we see the current is similar to heat flow, where the temperature difference between the objects indicates the voltage or electrical potential difference.

Similarly, if two charged objects have a potential difference and are connected by a conductor, a positive charge flows from the higher potential object to the lower one. This charge flow from conductor to conductor does not depend on the total charge of the two conductors. 

It depends on the electrical condition of the two conductors. This electrical state of the object is called electrical potential or voltage. 

So, voltage is the state of two charged objects having a potential difference that indicates the flow of charge from one object to another when they are connected to each other.

Formulas of Voltage

The amount of work required to move a single positive charge from one point to another in an electric field is a measure of the potential difference.

If we symbolized voltage as V, work done as W, and charge as q, then the voltage


So, Voltage = Work/Charge 

We find the voltage, current, and resistance relationship from Ohm's law. From this law, we find a mathematical representation of voltage as follows


So, Voltage = Current x Resistance

Where V is the voltage, I is the current and R is the resistance.

Voltage is also related to power and current and the relationship is as follows


So, Voltage = Dissipated Power/Current

Now let's know about the SI and CGS unit of voltage.

Unit of Voltage

SI Unit of Voltage: The SI unit of voltage is Joule/Coulomb (J/C) or Volt (V).

1 Volt: If 1J of work is required to bring a positive charge of 1C from an infinite distance to a point in an electric field, the potential at that point is called 1V.

CGS Unit of Voltage: The CGS unit of voltage is erg/statcoulomb or statvolt (statV)

1 statvolt is equal to 299.792458 volts.

Difference between EMF and Voltage

There is a difference between EMF and voltage -

One of the major differences is voltage causes current to flow between two points where EMF is the energy supplied to the charge.

EMF maintains the potential difference or voltage between two electrodes i.e EMF has constant intensity with a higher magnitude where the intensity of voltage is lower than EMF and it is non-constant.

The EMF on any source is measured by using a potentiometer where the voltage in an electric circuit is measured by a voltmeter.

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