Where can I start to learn electricity

Ohm's law

Ohm's law is the subject of this article. We explain to you here how this law links the physical quantities current, voltage and resistance. In addition, I will show you an application of Ohm's law in a "circuit" and also deal with the concept of the voltage source.

Ohm's law is a very important basis of electrical engineering. Even people who have nothing to do with this area of ​​physics often know it. Because it shows the relationship between current, voltage and resistance. If an electrical voltage is applied to an object, the strength of the electrical current flowing through it changes proportionally to the voltage. If you are not yet familiar with terms such as current, voltage and resistance, you should definitely read our article on them first.

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Calculate with Ohm's law

After you know (hopefully) what current, voltage and resistance is through the link just mentioned, you can now go directly to the equation of Ohm's law. This provides the connection: Voltage = Resistance · Current. This looks like this as a formula:

Ohm's law formula / equation:

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


Example: The resistance is 10 ohms and 5 amps flow. How big is the tension? Answer: U = 10 ohms x 5 amps = 50 volts. Or in short: U = 10 Ω · 5 A = 50 V. The voltage is therefore 50 volts. So if you have two of the three sizes, you can use them to calculate the third size.

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Application to Ohm's law

I would like to show you another application to Ohm's law here. It's about a small circuit. This includes a voltage source that generates the required voltage. There is also a resistor and copper wires that connect the voltage source to the resistor. But before we show the circuit, first the three symbols that are important for it.

Table scrollable to the right
symbolimportance
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 this picture, the current flows "up" out of the voltage source, along the conductor through the resistor, and over the two corners down into the negative connection of the voltage source. Otherwise Ohm's law also applies here: U = R · I. In some cases, you also write how great the resistance is, how much current flows or how great the voltage is.

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