How is electricity

Electric current / Electric current I

The electric current or strength of electric current is simply called current. This describes the transfer of electrical energy and the numerical movement of free charge carriers. Charge carriers can be electrons or ions.

An electric current can only flow if there are enough free and mobile charge carriers between two different electric charges. For example in a conductive material such as metal, liquid and gas.


  • Direct current
  • Alternating current
  • Eddy current

Comparison of current flow

The flow of electricity is often compared to running water in a pipe. The more the water flows through the pipe, the higher the amount of water. It is the same with electricity. The more electrons that flow through the conductor in one second, the greater the electrical current.
The electrical current strength is used to numerically describe the electrical current.


1000 A = 1 kA (kiloampere)
100 A (ampere)
10 A (ampere)
1 A (ampere)
0.1 A = 100 mA (milliamps)
0.01 A = 10 mA (milliamps)
0.001 A = 1 mA (milliamps)
0.0001 A = 100 µA (microamps)

The legal basic unit of electrical current is 1 ampere (A). The current values ​​in electronics are normally between a few microamps (µA) and several amps (A). In heavy current engineering, one also knows kiloampere (not specified).

Formula symbol

I: Electric Current
i: instantaneous value of an alternating current
î: peak value of an alternating current
I.TOTAL : Total current
I.R1 : Current through resistor R1

The symbol of the electric current or the electric current strength is the capital "I". Deviating from this, there are different spellings in upper and lower case with additional symbols that have a specific meaning. A number or letters as an index identify a specific current in a circuit.

Calculation formulas

There are various formulas for calculating the electrical current.

Current direction

The current direction is indicated in circuits with an arrow. Due to different scientific assumptions and findings, two current directions are defined.

  • The technical current direction (historical current direction) runs from plus (+) to minus (-).
  • The physical flow direction (flow direction of the electrons) runs from minus (-) to plus (+).
  • The current is shown in circuits with a (red) arrow in the technical direction of the current.

Technical direction of current (historical direction of current): From plus to minus

Before we knew the processes in atoms and the relationship between electrons, it was assumed that positive charge carriers were responsible for the flow of electricity in metals. Accordingly, the current should flow from the positive pole to the negative pole. The use of a measuring device to measure current also allows this conclusion. Although the assumption at that time was refuted, the original (historical) direction of the current was retained for practical reasons. That is why the current direction within a circuit is still defined from plus to minus today.

Physical flow direction (electron flow direction): From minus to plus

In a closed circuit, free charge carriers (electrons) are repelled from the negative pole and attracted to the positive pole. This creates a flow of electrons from the negative pole to the positive pole. This current direction is the physical current direction, which is also called the electron current direction. It corresponds to the actual flow direction of free charge carriers.

Measure the electric current

The ammeter is always connected in series with the consumer. To do this, the line of the circuit must be disconnected in order to be able to insert the measuring device into the circuit. The current must flow through the measuring device during the measurement.

Electricity in electronics

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