What is the electrical series resistance in the capacitor

Capacitive reactance

Basically, two or more conductive surfaces that are insulated from one another are to be regarded as capacitors or capacitors. This includes all cables, conductors and connectors. Two parallel cables or conductors cause a capacitive reactance. Especially in high-frequency technology, the resulting capacitances can influence the function of a circuit. However, much more complex models and formulas are used in high-frequency technology than is described below.

AC voltage capacitor

A capacitive reactance is a capacitor with alternating voltage. In a direct current circuit, the capacitor acts like an infinitely large resistor. Comparable to an interruption of the circuit, with the exception of the short charging current. In the AC circuit, the capacitor lets the current through. Here, too, it acts like a resistance. Due to the constantly changing direction of current, the capacitor is constantly charged and discharged. A current flows through it practically all the time, with no real flow taking place. The capacitor absorbs energy when it is charged, stores it and releases it again when it is discharged. The energy is pushed back and forth with no effect. That is why it is also called reactive energy and resistance is called reactance. In this case it is the capacitive reactance.

Current and voltage are out of phase with one another. The voltage lags the current by 90 °. It is also said that the current leads the voltage by 90 °. The shape of the curve is not changed by the capacitor. The reason is the charging and discharging behavior of the capacitor. Whenever the voltage changes, a current flows. With AC voltage, the voltage changes constantly. The current has always reached its peak value or the highest point when the alternating voltage changes the most. That is in the zero crossing. This is where the sine wave of the voltage is steepest.
The current flow ends when the applied voltage has reached its highest point, the peak value. That is where the sine wave of the voltage is flattest.

The capacitive reactance can be calculated with the help of Ohm's law and the effective values ​​of voltage and current.

Frequency dependence


The capacitive reactance is influenced by its capacitance and the frequency of the applied alternating voltage. The capacitive reactance of the capacitor is greater, the smaller the capacitance of the capacitor and the lower the frequency of the applied voltage. The smaller the capacity, the faster the capacitor is charged. The current is smaller and therefore the resistance is greater. The small j is the imaginary part.

The diagram shows the course of the capacitive reactance XC. depending on the frequency. The resistance value decreases with increasing frequency.

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