Video: Eg17S1-Physics-Q37A

State one factor that affects the capacitive reactance of a capacitor.

01:23

Video Transcript

State one factor that affects the capacitive reactance of a capacitor.

Now in order to answer this question, let’s start by thinking about a capacitor in a circuit. So here’s our capacitor at the bottom of the circuit, which has a capacitance 𝑐 and is connected to an AC source, which is giving out a frequency, let’s say, 𝑓. Now it’s at this point that we can recall that the capacitive reactance of the capacitor is defined as 𝑋 subscript 𝑐 — that’s the capacitive reactance — is equal to one divided by two 𝜋 multiplied by the frequency produced by the AC source multiplied by the capacitance of the capacitor.

Now it’s worth noting by the way that the AC source produces a sinusoidally oscillating potential difference. And that potential difference has a frequency 𝑓. But as a result of this, the current flowing through the circuit will also be sinusoidally oscillating with the same frequency, 𝑓. It’s not necessary that the current has the same phase as the voltage. But the frequency will be the same.

So anyway, coming back to the capacitive reactance of our capacitor then, we can see that it’s affected by two different factors. Firstly, the frequency produced by the AC source, and secondly the capacitance of the capacitor. Naturally, two 𝜋 is just a constant. So that’s not going to change, which means that if we have to state one factor that affects the capacitive reactance of a capacitor, then we can choose to state 𝑓 or 𝑐 as our answer.

Therefore, one factor that affects the capacitive reactance of a capacitor is the current frequency in the circuit. And another factor is the capacitor’s own capacitance. We can choose to give either one of these as the answer to our question.

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