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Electric voltage explained simply

The electrical voltage is simply explained in this article. Summary of the content:

  • A Explanationwhat the electrical voltage is.
  • Lots Examples all about tension and tension.
  • tasks / Exercises to tension.
  • A Video, which deals with the basics of electrical engineering.
  • A Question and answer area around the tension.

This article is part of our electrical engineering course "From the basics of electrical engineering in 5th grade to becoming an engineer".

Explanation of electrical voltage

In the basics of physics you learn that there are electrical charges. When these charges move, an electric current is generated. And with that we can also look at the electrical voltage right away.


The electrical voltage shows how strong the drive of the electrical current is. It is basically the "kick in the buttocks" of the charges so that they move. The greater the tension, the stronger the drive.

How high the electrical voltage is is given in volts. This unit is abbreviated with a "V". The symbol is a capital "U". The electrical voltage is then used for this "U", for example 5 V.

Electrical voltages are generated by voltage sources. A voltage source has two connections: plus and minus. In electrical engineering, one often draws plans with all the components. The voltage source is drawn in these plans as follows:

This was the general circuit symbol for a voltage source. You can also generate voltages with a battery. In this case the symbol is drawn in the circuit as follows:

Open circuit voltage and terminal voltage:

We have just seen that a voltage source has two outputs. You can also measure the voltage between these. There are two different types of measurement:

  • Open circuit voltage: The open circuit voltage is the electrical voltage measured at the terminals of an unloaded voltage source. In other words: We have a voltage source to which nothing is connected and we use a measuring device to measure the voltage it emits.
  • Terminal voltage: This is the voltage that is present between the terminals of the voltage source. If the voltage source is loaded by a consumer such as a lamp, the terminal voltage drops (unless technical countermeasures are taken).

DC voltage and AC voltage:

The article on electric current briefly discussed direct current and alternating current. This is also available for voltage with direct voltage and alternating voltage.

  • DC voltage: In the case of a direct voltage, the voltage is the same, i.e. at every point in time it has the same sign and the same amount. One speaks of DC voltage when the DC component has priority over a periodic voltage. In other words: If there is a constant voltage of 3 V for 10 seconds, we have a DC voltage for this period of time.
  • AC voltage: An electrical voltage is called alternating voltage if its polarity changes in regular repetition, but its mean value over time is zero. In other words: The voltage is, for example, 4 V, then goes down to -4 V, rises again to + 4 V, etc. And this regularly as a so-called sine function. AC voltage is present at the socket in the house.

Electric voltage formula:

There are numerous formulas for calculating electrical voltages. Two of these formulas are presented here. The first formula or equation establishes the relationship between voltage, work and charge. Please do not be surprised that terms appear here that have not yet been explained. They will be dealt with in subsequent articles, but the formulas should be included here for the sake of completeness.

Or expressed in words:

A second formula establishes the relationship between current, voltage and resistance. It's the formula behind Ohm's law.

Or expressed in words:


Examples of electrical voltage

In this section, a number of examples of electrical voltage will be dealt with.

example 1:

Name a number of electrical devices that require voltage to operate.


You can name a lot of devices and machines here. Here are a few options:

  • Refrigerators
  • Freezers
  • cars
  • Planes
  • TV
  • Smartphones / cell phones
  • printer
  • Air conditioners

Example 2:

Given a current of 3 amps with a resistance of 10 ohms. How big is the tension?

We know current and resistance, so we use the formula U = R · I. Here we insert the information and get the voltage to U = 30 ΩA. This corresponds to U = 30 V.

Tasks / exercises electrical voltage


Videos on tension

Basics of electrical engineering

The next video shows the basics of electrical engineering. It is about learning the basic connections in this area. The electrical voltage is also dealt with and how it is used in Ohm's law.

Next video »

Questions with answers electrical voltage

This section deals with typical questions about electrical voltage.

Q: What other topics should I check out?

A: For the basics of electrical engineering and magnetism, you should still have a look at these topics:

Take a look at these and other topics under Learning Electrical Engineering.