The alternating current (AC) is also interesting. In the above picture you can see a diagram of that which is used in the houshold. If you switch on the TV or use a computer, you only need one of the phases shown here. You may also have noticed, that voltage not only rises to 220- or 230 V, but even higher. This is due to the RMS-(Root Mean Square)value, also called the effective value, which is always given for this type of voltage, a sort of average with which e.g., also the extracted energy can be better calculated.

All three phases are needed, e.g., by the electric kitchen stove (cooker, range), although, inside the stove they are once again, divided up. If workshop devices, which use a great deal of electricity and require the high- voltage current of 400 V, this has to be installed, e.g., for a high-performance compressor or similar equipment. The right-hand arrow shows how the 400 V are arrived at. In this case, it's different from 230 V, where the individual phases are measured against the neutral lead, here, all the phases are measured against each other, which gives the respectively greater distance. Of course, once again the effective value and not the peak value is what is meant here.

This type of alternating current is also found in motor vehicles. Since always, when electricity is generated, it starts out as alternating current. Therefore, you can learn more more about it's production here. In the motor car the alternating current is converted into direct current (DC), so that it can be stored. Thus, alternating current is found less often in motor cars, except for when it is digital and a voltage is often and regularly changed.

There are components, whose function is only accessible with alternating current and the variations thereof. What the resistor is for the DC-circuit, the condenser is for the AC- circuit. It is also described as being the charge accumulator. At the top, in picture 2, you can see a larger amount, with which BMW once wanted to store electric energy in the prototypes of it's elecrically driven cars. Because, although the charging was much faster than with a battery, the AC current also switched over much faster, thus the voltage peaks had to be cut back a bit.

If you have a look at the resistor and the condenser as being serially switched, the result is an RC-circuit. This in turn, has a lot of meaning for the DC-circuit. Whenever process steps have to be regularly triggered or smallest waiting periods are necessary, this type of circuit is found.

While on the subject of changing voltages, the coil must be mentioned, also in the case of the DC-circuit. First of all, the creation of a magnetic field is important, possibly amplified through a magnetised core. Which electrically operated valve, which electric motor or which power-relay could get by without a coil? In addition, there is also the restricting effect in the case of larger voltage fluctuations. 09/13