What is reactance of a capacitor

It is reasonable to assume negligible resistance, since in practice we can make the resistance of an inductor so small that it has a negligible effect on the circuit. Also shown is a graph of voltage and current as functions of time.

Figure 1. The graph in Figure 1 b starts with voltage at a maximum. Note that the current starts at zero and rises to its peak after the voltage that drives it, just as was the case when DC voltage was switched on in the preceding section. When the voltage becomes negative at point a, the current begins to decrease; it becomes zero at point b, where voltage is its most negative.

The current then becomes negative, again following the voltage. The voltage becomes positive at point c and begins to make the current less negative. At point d, the current goes through zero just as the voltage reaches its positive peak to start another cycle. This behavior is summarized as follows:. Current lags behind voltage, since inductors oppose change in current.

This is considered to be an effective resistance of the inductor to AC. X L is called the inductive reactance , because the inductor reacts to impede the current. It makes sense that X L is proportional to L , since the greater the induction the greater its resistance to change. It is also reasonable that X L is proportional to frequency f , since greater frequency means greater change in current.

The greater the change, the greater the opposition of an inductor. For the first frequency, this yields. The inductor reacts very differently at the two different frequencies. At the higher frequency, its reactance is large and the current is small, consistent with how an inductor impedes rapid change.

Thus high frequencies are impeded the most. Inductors can be used to filter out high frequencies; for example, a large inductor can be put in series with a sound reproduction system or in series with your home computer to reduce high-frequency sound output from your speakers or high-frequency power spikes into your computer. Note that although the resistance in the circuit considered is negligible, the AC current is not extremely large because inductive reactance impedes its flow.

With AC, there is no time for the current to become extremely large. Consider the capacitor connected directly to an AC voltage source as shown in Figure 2. The resistance of a circuit like this can be made so small that it has a negligible effect compared with the capacitor, and so we can assume negligible resistance.

Voltage across the capacitor and current are graphed as functions of time in the figure. Figure 2. The graph in Figure 2 starts with voltage across the capacitor at a maximum. The current is zero at this point, because the capacitor is fully charged and halts the flow. Then voltage drops and the current becomes negative as the capacitor discharges. The current remains negative between points a and b, causing the voltage on the capacitor to reverse.

This is complete at point b, where the current is zero and the voltage has its most negative value. The current becomes positive after point b, neutralizing the charge on the capacitor and bringing the voltage to zero at point c, which allows the current to reach its maximum. English Spanish. Enable Cookies. Go Back. Search Delivery. The formula for calculating the Capacitive Reactance, or impedance of a capacitor is: Capacitive reactance, denoted as x sub c X C , is equal to the constant one million or divided by the product of 2 p or 6.

Just a moment This application uses your local weather and energy rates. Instead they have to be summed "vectorially". In other words it is necessary to square each value, and then add these together and take the square root of this figure.

Put in a more mathematical format:. By adding the two quantities in this way it is possible to calculate the overall impedance for the combination of resistor and capacitor. It is also possible to use Ohm's law to calculate the current and voltage, etc in the normal way. Capacitive reactance is a key quantity in all forms of electrical electronic circuit.

As capacitors are used in virtually all electronic products, understanding how to calculate the reactance and how this interacts with resistors and other electronic components is a key element for many electronic circuit designs. Even though the calculations are relatively straightforward, they are very important in many areas. What is capacitive reactance In a direct current circuit where there may be a battery and a resistor, it is the resistor that resists the flow of current in the circuit.

Capacitive reactance vs frequency Calculating the reactance of a capacitor It can be imagined that the larger the capacitor, the more charge it can store and hence the less it will restrict current flow. Shopping on Electronics Notes Electronics Notes offers a host of products are very good prices from our shopping pages in association with Amazon.

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