Electrical polarity

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

The pole as a connection point

In an electrical circuit, an electrical component ( eg battery, bulb ) must be connected so that electric charge can flow. This requires that ( at least) two connection points, called poles, so that the charge carriers can flow at a location in and out at the other. For the connection of a device, there is therefore (at least) two ways which differ in the direction in which the current flows through the device. When the direction of current for the device plays a role, the electrical connections must be made with the correct polarity, that is, the two poles must be correctly assigned.

An electric voltage always has two poles between which there is a potential difference. With DC voltage, these are the positive pole (positive pole, briefly Plus sign or anode) and the negative pole ( negative, short minus sign - or cathode). Individual electric poles at voltage sources do not exist.

When AC voltage, the poles periodically change their polarity.

History

When Bernstein, a glass rod, a resin or sealing-wax on wool or fur rubbing, you notice that slight body (eg dust) tightened. The phenomenon already knew the Greeks are amber, they "electron" called. This area of physics eventually became the theory of electricity.

It was found that the charge occurring (e.g., that of the glass rod ) is always opposed to an equal opposite charge. Uniting to the two resulting charges so they cancel each other ( neutralize ). The charges arise from a charge separation that occurs when rubbed. Large Meyers encyclopedia 1905 writes:

Thus, it was determined which of the two poles as positive and which can be described as a negative pole - the " glass electricity" was defined as "positive", regardless of which (eg grated bar, battery, dynamo, flash) the potential difference is produced between the poles. Later, those particles were discovered in respect of which the resin ( amber ) electricity is " negative," was the Greek name for amber - electron - transfer to these particles and thus electrons were negative charge carriers.

Technical significance

For batteries, accumulators and electrochemical elements results in the polarity of the electrochemical series. With thermocouples it results from the thermoelectric voltage range.

With DC voltage prevails in metallic conductors to the positive terminal to the negative terminal electron deficiency and an excess of electrons.

The positive pole of the color red and the negative terminal is usually associated with the color blue or black.

Reverse polarity protection

Many devices and modules ( sensors, batteries, plugs) are protected against confusion of the poles ( reverse polarity ). Either they are electrically protected - an incorrect connection leads in this case not to destroy, but at most to a fuse blowing - or mechanically by suitably shaped plug or differently shaped contacts ( for example, the different diameter of the pole bolt a car battery ).

Polarity with AC voltages

When AC voltage, the polarity is used is also often prescribed to achieve a correct phases or potential assignment. Examples include speakers or the windings of transformers and transformers. Since the identification with " " and "-" would be misleading (but still sometimes takes place ), the following terms have been established:

• "Cold" for ground and "hot" for the opposite pole ( Communications Engineering, with symmetrical signal transmission even for the 0 ° - and 180 ° - phase)
• Neutral to ground potential and the outer conductor or " phase " for the opposite pole ( power supply )
• Asterisk for connections the same phase (identification of windings of transformers in a circuit diagram)
• Red and black ( or any color code ) for in-phase connection of speakers and speaker boxes

Determining and measuring

The type of a pole opposite the antithesis or opposite Earth can be determined as follows:

• With a voltmeter: it shows the ( right ) polarity by a (missing ) at minus sign or direction of the pointer deflection;
• The Polart compared to ground potential by an electric field meter.

Additional tools:

• In a phase tester or a neon lamp lights when the DC voltage, the negative electrode (cathode).
• Exploiting the behavior of a diode: it is a technical current direction ( positive to negative ) (eg a light bulb ) connected in series to a consumer, may only be current when its cathode is towards the negative pole. The symbol of the diode indicates the direction of current;
• At high voltage with a test charge (see electrostatic attraction ).