# Electric pole

An electrical pole is one of two points between which there is electrical voltage . The assignment or arrangement of the two poles is called polarity or polarity .

## The pole as a connection point

Battery with plus and minus pole
Electrolytic capacitor with plus and minus pole

In an electrical circuit , an electrical component (e.g. battery , incandescent lamp ) must be connected in such a way that electrical charge can flow through it. This requires (at least) two connection points, called poles, so that the charge carriers can flow in at one point and out the other. There are therefore (at least) two options for connecting a component, which differ in the direction in which the current flows through the component. If the direction of current plays a role for the component, the electrical connection must be made with the correct polarity, i.e. the two poles must be assigned correctly.

An electrical voltage always has two poles, between which there is a potential difference . In the case of direct voltage, these are the positive pole ( positive pole , short plus, sign + ) and the negative pole ( negative pole , short minus, sign - ). There are no individual electrical poles in voltage sources.

With AC voltage , the poles periodically change their polarity.

### history

If you rub amber , a glass rod, a resin or a sealing wax rod on wool or fur , you will notice that light objects (e.g. dust ) are attracted. The Greeks were already familiar with this phenomenon from amber, which they called "electron". This area of physics later became electricity .

It was found that the resulting charge (e.g. that of the glass rod) is always opposed to an equally large opposite charge. If the two charges created are combined, they cancel each other out (neutralize each other). The charges arise from a charge separation that occurs when rubbing. Meyers Großes Konversationslexikon 1905 writes:

Two quantities that behave in this way are called opposites, one as positive, the other as negative. .... The phenomena themselves give us no hint as to which of the two is to be regarded as positive; but it was agreed that glass electricity should be called positive and resin electricity negative. "

It was therefore determined which of the two poles is to be designated as the positive and which as the negative pole - the "glass electricity" was defined as "positive", regardless of what (e.g. rubbed rod, battery, dynamo, lightning) the Potential difference between the poles is established. When the particles were later discovered, because of which the resin (amber) electricity is “negative”, the Greek name for amber - electron - was transferred to these particles and electrons became negative charge carriers.

### Technical importance

Car battery (accumulator) with plus ( red ) and minus ( black ) pole

For batteries , accumulators and electrochemical elements , the polarity results from the electrochemical series of voltages . For thermocouples it results from the thermoelectric series of voltages .

With DC voltage , there is a lack of electrons at the positive pole and excess electrons at the negative pole in metallic conductors.

The positive pole is usually assigned the color red and the negative pole the color blue or black .

#### Reverse polarity protection

Many devices and assemblies ( sensors , batteries, plugs) are protected against mixing up the poles ( polarity reversal ). Either they are electrically protected - in this case a wrong connection does not lead to destruction, but at most to a fuse  release - or mechanically by means of suitably shaped plugs or differently shaped contacts (for example the different diameters of the pole bolts of a car battery ).

#### Polarity for alternating voltages

In the case of alternating voltage, the pole assignment is also often prescribed in order to achieve a correct phase or potential assignment. Examples are loudspeaker boxes or the windings of transmitters and transformers. Since the designation with "+" and "-" would be misleading (but still sometimes done this way), the following terms have established themselves:

Schuko plug (2-pin) and socket in the mains

#### Determination and measurement

The type of pole opposite the opposite pole or opposite earth can be determined as follows:

• with a voltmeter : it shows the (correct) polarity with a (missing) minus sign or the direction of the pointer deflection;
• the polar type versus earth potential with an electric field meter .

Further resources: