What are the basic electrical questions

Electric circuit

We will deal with the electrical circuit in this article. We explain to you what an electrical circuit is and provide you with definitions of basic terms in electrical engineering. In this context we also go into Ohm's law. This article belongs to the field of physics / electrical engineering.

In an electrical circuit there is usually:

  • A voltage source or current source
  • A conductor (e.g. a copper wire)
  • A consumer (e.g. a lamp)

A consumer has what is known as an internal resistance. This ensures that voltage drops inside the consumer. We'll go into more detail about the terms current, voltage and resistance in a moment. Another note on the side: A source also has an internal resistance at which voltage drops. We will come to this in further articles. But first the table with symbols and their meaning.

Table scrollable to the right
Symbol for a voltage source.
Symbol for a resistance.
Symbol for a conductor (e.g. copper line)

And all of this is now assembled into a small circuit. It looks like this:

Important note: In electrical engineering, the current direction is specified from "+" to "-". In physics, this is usually the other way around. This is extremely confusing for beginners in electrical engineering, but this is (unfortunately) how it is handled. Since we are discussing things from electrical engineering here, the current flows from "+" to "-"!

In order not to get confused with the terms current, voltage and resistance in the electrical circuit, brief information about these three important terms in electrical engineering follows.


Electric current is the term used to describe the movement of charge carriers through a substance or through an empty space (vacuum). Charge carriers are, for example, electrons or ions. So if electrons move through a copper wire, for example, we speak of current flow. Think of it like a river (water) in nature. There also water flows in a river bed. And so electrons flow in a copper wire.


There are prerequisites for many things in life: In order for a person to survive, he has to breathe. There are also requirements for electricity. So the current needs voltage to flow. The electrical voltage is understood to be the driving force that causes the charge movement. Basically, the higher the voltage, the more current can flow.


Resistance is, so to speak, the "opponent" of tension. Because voltage drops at every resistor, i.e. becomes less. And we have already said about voltage: the lower the voltage, the less current can flow. A resistor is an electronic component that can be bought for (very little) money. An electronic conductor, for example a copper wire, also has its own resistance at which voltage drops. The information on current, voltage and resistance can be calculated using Ohm's law (will be dealt with in the following chapter).


Electrical circuit and Ohm's law

Ohm's law is the most important formula in electrical engineering and links the quantities current, voltage and resistance in an electrical circuit. Even people who have nothing to do with this area of ​​physics often know it. Ohm's law says: Voltage = Resistance · Current. This looks like this as a formula:

Ohm's law:

  • Formula: U = R * I
  • "U" is the voltage in volts, e.g. B. 1 V
  • "R" is the resistance in ohms, e.g. B. 1 Ω
  • "I" is the amperage in amperes, e.g. B. 1 A

Example: Let's apply this knowledge to the electronic circuit. The resistance is 10 ohms and 5 amps flow. How big is the tension? Answer: U = 10 ohms x 5 amps = 50 volts. The voltage of the source is therefore 50 volts. So if you have two of the three larger ones, you can use them to calculate the third size.


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