What is Voltage

Voltage is one of the basic parameters that describes the electrical conditions in a circuit - measured in volts, it is a key parameter.

Voltage Includes:
What is voltage     Electric field    

Voltage is one of the fundamental parameters associated with any electrical or electronic circuit. Voltage is seen widely in specifications of a host of electrical items from batteries to radios and light bulbs to shavers, and on top of this it is a key parameter that is measured within circuits as well.

The operating voltage of an item of equipment is very important - it is necessary to connect electrical and electronic items to supplies of the correct voltage. Connect a 240 volt light bulb to a 12 volt battery and it will not light up, but connect a small 5V USB device to a 240 volt supply and far too much current will flow and it will burn up and be irreparably damaged.

On top of this, the voltage levels within a circuit give a key to its operation - if the incorrect voltage is present, then it may give an indication of the reason for the malfunction.

For these and many reasons, electrical voltage is a key parameter and knowing what the voltage is can be a key requirement in any circumstance.

Voltage basics

Voltage can be considered as the pressure that forces the charged electrons to flow in an electrical circuit. This flow of electrons is the electrical current that flows

What is voltage
Voltage shown within a simple circuit

If a positive potential is placed on one end of a conductor, then this will attract that negative charges to it because unlike charges attract. The higher the potential attracting the charges, the greater the attraction and the greater the current flow.

The higher the voltage potential difference, the greater the attraction of electrons and greater the current flow
The higher the voltage potential difference, the greater the attraction of electrons and greater the current flow

In essence, the voltage is the electrical pressure and it is measured in volts which can be represented by the letter V.

Normally the letter V is used for volts in an equation like Ohm’s law, but occasionally the letter E may be used - this stands for EMF or electro-motive force.

To gain a view of what voltage is and how it affects electrical and electronic circuits, it is often useful as a basic analogy to think of water in a pipe, possibly even the plumbing system in a house. A water tank is placed up high to provide pressure (voltage) to force the water flow (current) through the pipes. The greater the pressure, the higher the water flow.

Alessandro Volta

The unit of electrical potential is the volt which is named after Alessandro Volta, an Italian physicist who lived between 1745 and 1827.

Note on Alessandro Volta:

Alessandro Volta was one of the pioneers of dynamic electricity. Investigating the basic properties of electricity, he invented the first battery and advanced the understanding of electricity.

Read more about Alessandro Volta.

Potential difference

The electrical potential or voltage is a measure of the electrical pressure available to force the current around a circuit. In the comparison of a water system mentioned when describing current, the potential can be likened to the water pressure at a given point. The greater the pressure difference across a section of the system, the greater the amount of water which will flow. Similarly the greater the potential difference or voltage across a section of an electrical circuit, the greater the current which will flow.

What is a volt

The basic unit of voltage is the volt, named after the Italian scientist, Alessandro Volta, who made some early batteries and performed many other experiments with electricity.

The volt definition:

The standard unit of potential difference and electromotive force in the International System of Units(SI), formally defined to be the difference of electric potential between two points of a conductor carrying a constant current of one ampere, when the power dissipated between these points is equal to one watt.

To give an idea of the voltages which are likely to be encountered, a CB radio will usually operate from a supply of around 12 volts (12 V). The cells used in domestic batteries have a voltage of around 1.5 volts. Rechargeable Nickel Cadmium cells have a slightly smaller voltage of 1.2 volts, but can normally be used interchangeably with the non-rechargeable types.

In other areas voltages much smaller and much greater than this can be encountered. The signal input to an audio amplifier will be smaller than this, and the voltages will often be measured in millivolts (mV) or thousandths of a volt. The signals at the input to a radio are even smaller than this and will often be measured in microvolts (µV) or millionths of a volt.

At the other extreme much greater voltages may be heard about. The cathode ray tubes in a television or computer monitors require voltages of several kilovolts (kV) or thousands of volts, and even larger voltages of millions of volts or megavolts (MV) may be heard of in conjunction with topics like lightning.

EMF and PD

The voltage for a battery or single cell is stated as a voltage. However it is found that when the battery is in use its voltage will fall, especially as it becomes older and it has been used. The reason for this is that there is some resistance inside the cell. As current flows a voltage drop forms across this and the voltage seen at the output is less than expected. Even so the voltage seen at the terminals if the battery was not supplying current would still be the same. This no load voltage is known as the electro-motive force (EMF), and is the internal voltage which is generated by the cell, or other source of power.

How to measure voltage

One of the key parameters that needs to be known in any electrical or electronic circuit is the voltage. There are several ways in which voltage measurements can be made, but one of the most common is to use a multimeter. Either analogue or digital multimeters can be used, but these days digital multimeters are most commonly used as they are more accurate and are available for very reasonable prices.

Note on how to measure voltage with a Multimeter:

Voltage is one of the key parameters that needs to be known in any electrical or electronic circuit. Voltage can easily be measured using an analogue or digital multimeter where accurate readings can be taken very easily.

Read more about how to measure voltage.

More Basic Concepts:
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