Capacitance and inductance are two concepts in electrical engineering that don’t get a lot of attention, but they’re important. They’re commonly used to find the ratio of energy stored in an electric field to the energy dissipated as heat. For example, if you had a capacitor and it was storing energy at 1 volt, there would be 1 farad of capacitance. If you had a voltage source with 2 volts across it that was dissipating 2 watts as heat, then the inductance formula would say there is 0.5 henrys per volt across the point that the current is flowing through, or 500 millihenrys (mH) total—the symbol for mH is mh.
A capacitance c and an inductance l are operated at the same angular frequency. When you operate two different reactances at the same frequency and compare them, you’d say that c to the nth power is equal to l to the (n-1)th power. In other words: c n = l (n-1) . This equation provides very useful data for engineers because when a circuit is resonating, it’s dissipating energy and creating heat. Inductance is a reactance that’s very easy to calculate, as opposed to capacitance, which can be difficult. For example: let’s say you have a 1 mH inductor and a 1 microfarad capacitor; this is an LRC (inductive-capacitive) resonant circuit.
1. Inductance :
Inductance is measured in henry, a unit that’s named after Henry Joseph Carey, an American physicist and engineer who invented it. It’s the measure of magnetic flux (intensity) around a loop. A coil will have more inductance than the manufacturer claims if you don’t run the internal resistance down to 0 ohms.
The gauge of wire is how much inductance it has per turn: 80-gauge wire has about 1/4 henry of inductance per turn or about 6 inches or 16 cm across. You can find out how many turns are in an inductor by dividing by its diameter and then multiplying by 1,000 (1 inch × 10 gauge = 100 feet).
2. Capacitance :
Capacitance is measured in farads, a unit that’s named after André-Marie Ampère, a French physicist and mathematician. A capacitor is a charged storage space much like an electric battery; however, they differ in ways that have to do with the surface area of their electrodes (plates) and the materials between them.
A capacitor can also be made up of many small capacitors (called multiples of Farad) bonded together. To calculate capacitance, you divide the mass by the charge: C = m / q = µ F / nC = µ B / nC The number of microfarads per farad is 0.001. The mass is measured in microcoulombs, an electric charge measured in coulombs. The number of nanoFarads per farad is 0.000000001 or equal to 1×10−9 or one trillionth.
3. LRC ( Inductive- Capacitive) Resonance :
To understand how resonance works, imagine a load connected across one end of a resistor and another resistor connected across the other end of the load resistor. When the source of voltage (resistor) is connected across both resistor points, it creates a large voltage drop that would ordinarily fall across both resistors. But because energy is conserved, there’s no extra voltage to dissipate as heat in the second resistor.
When this happens, the load (second resistor) will get very hot! When you use two inductors and a capacitor connected together in a series-parallel combination, this results in an increase in voltage at resonance for alternating current (AC). This type of circuit works better for high frequencies as opposed to low frequencies. Let’s say you have two capacitors, one of which is charged to 4.8 microfarads while the other is charged to 0.1 microfarads.
The total capacitance would be 2.2 microfarads, but since the second capacitor is charged to only 0.1 microfarads, it has a small effect on the overall circuit, compared with the larger capacitor of 4.8 microfarads. So in reality, a resonant circuit with only a small capacitor will actually have very little reactance and will work well at frequencies over 1 kHz and less than 40 kHz—a fraction of a cycle (Hz).
4. LCR ( Inductive- Capacitive-Reactive) Resonance :
The LCR resonant circuit is basically the same as the LRC circuit. It differs only in the addition of an inductor. If a capacitor has a high reactance, but a low resistance, you can add an inductor to reduce the reactance to zero. Since there’s no reactive component to an inductor and a magnetic field is created around it when it’s in motion, this will work well at frequencies that are greater than 1 MHz and less than 15 MHz—the range of highest impedance (Xmax).
If you’re learning about electric fields and want to know how to learn about capacitance and inductance, then this article is for you.