Electric current, often just current, is a physical phenomenon in the field of electricity. In the everyday meaning of the term, it refers to the transport of electrical charge carriers, such as electrons in conductors or semiconductors or ions in electrolytes. This form of current is also known as a convection current. As described by Ampere’s law, it is manifested by a magnetic field and usually leads to heating of the conductor. In a closed electrical circuit, a current flows continuously as long as there is a conductive connection between the connections of the source. For a short time, after connecting a conductor to a voltage source, a current flows even in an open circuit, which charges or discharges the conductor until it is at the potential specified by the voltage source.
In addition, the displacement current is counted as an electric current. This is not caused by the movement of charges, but when an electric field changes in time. It occurs, for example, between the plates of a capacitor during charging or discharging and, like the convection current, generates a magnetic field. The physical quantity that measures the electric current is Ampere.
If, for example, there is a potential difference between the poles of a battery, this is referred to as an electrical voltage. Due to the then existing electric field, a force is exerted on the charge carriers; as a result, they experience acceleration when they are mobile. This happens, for example, when an incandescent lamp is connected to the poles via metal wires. The drift velocity of the charge carriers during this directional movement arises in interaction with scattering processes. The current density can be calculated by multiplying the drift velocity by the space charge density.
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In a circuit with a voltage source, its fixed electrical voltage and resistance determine the specific current. On the other hand, when a current source is used, its fixed amperage at the resistor builds up the specific voltage. In practice, however, voltage sources are much more common than power sources, such as in power supplies, which is why the specific value of the electrical current depends on the consumer (or more precisely: its resistance).
Effects of the Current
The occurrence of an electric current manifests itself in the following effects:
- Heat effect
- Magnetic effect, including force effect in own or external magnetic field
- Chemical action
- Lighting effect
In the case of alternating current (AC), there is a periodic change in the direction of the current. Each period consists of successive periods of positive and negative instantaneous values that complement each other to form an average current zero. The decisive factor for the success of alternating current for energy transport was that the voltage can be changed very easily with the help of transformers.
