Basic concepts of electrical engineering (Audi A4 B6)

Electric current can only flow in a closed circuit. An electric circuit consists of a current source (for example battery), consumers (for example, incandescent lamps, starter) and wires by means of which the source and consumers of current are connected to each other through switches, relays and fuses.

Imagine a water pipe in which a certain amount of water flows under a certain pressure: this system can be compared to an electrical circuit.

Voltage: Voltage corresponds to the water pressure in the water supply system and is measured in volts (V).

Current strength: Current strength corresponds to the amount of water flowing through a pipeline in a certain period of time. The unit of measurement for current strength is ampere (A).

Power: The product of voltage and current shows how much electrical energy the current source gives to the consumer. Power is measured in watts (W).

Resistance: Resistance can be compared to a shut-off valve in a pipeline. If the valve is fully open, the water flows unimpeded (resistance 0). If you close the tap, the resistance increases until the water stops flowing altogether (infinite resistance). The unit of measurement of resistance is Ohm.

Wires: The wires correspond to the pipes. The diameter of the pipeline depends on the consumer. For a control lamp, a wire with a cross-section of 0.5 mm² is sufficient, while a 16 mm wire is needed for a starter. A wire that is too thin heats up, and the voltage drops. In this case, for example, the voltage supplied to the headlight is not 12 volts, but, say, only 10 or 9.5 volts, and the headlight becomes dim.

[The article was copied from the website AUDImanual]