The Electrical Current

What Is This Actually?

The term "electrical current" implies that something flows. Many experiments and considerations resulted in the conclusion that in the case of an electrical current, electrically charged particles move in a conductor. These particles are called electrical charges.

The positive charges are bound to the atomic nucleus. So if the electrical current in a solid conductor was caused by the movement of the positive charges, this would also involve a shift of the atoms of the substance. In an electrical circuit, in which a copper wire was connected to an iron wire, the iron atoms eventually had to move through the copper wire, or vice versa. This could not be observed. Therefore, the following conclusion was reached: The electrical current in solid conductors consists of the flowing of electrons.

In a closed circuit, the electrons will therefore move from the negative pole to the positive pole. As long as the current is switched on, the flowing off electrons are replaced by new electrons from the negative pole of the power supply. At the negative pole there exists an electron surplus, at the positive pole there is a lack of electrons. The power supply drives the electrons from the negative pole over the closed circuit to the positive pole.

In a battery, there is an electron surplus at one pole compared with the other pole. If both poles are connected, for example via a bulb, an electron flow is generated, which always flows slowly in the same direction from the negative terminal to the positive terminal. An electrical current that constantly flows in the same direction is called direct current.

Before more exact details about the nature of the electrical current were known, the direction of the current was arbitrarily assumed to be from the positive to the negative pole. This has been kept as the technical direction of the current until today.

A glow lamp shows the polarity of a direct current power supply. The negative electrode becomes covered with a glowing light, whereas the positive electrode remains dark.

A Constant To and From: Alternating Current

The socket, however, does not supply direct current, but alternating current. A dynamo for a bicycle is an alternating current power supply as well.

From the shining of a light bulb, it is impossible to tell whether it is powered with direct current or alternating current. But it is possible with a glow lamp. When observed directly, both electrodes glow unevenly and flickeringly. If you observed the glow lamp in slow motion, though, you would notice that the electrodes were covered with an alternating glowing light.

In the case of the socket, the positive and the negative pole change constantly. In one second, the electrons move back and forth 50 times, they swing. Therefore, the alternating current from the socket has a frequency of 50 swings per second or simply 50 hertz (Hz). An electrical current that changes its direction periodically is called an alternating current.

Material courtesy of Kids&Science Foundation

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Last Update: 2004-Feb-29