Capacitor
Capacitor
A capacitor is a device used to store an electric charge, consisting of one or more pairs of conductors separated by an insulator. It is a passive electronic component with two terminals. The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. The capacitor was originally known as a condenser or condensator. This name and its cognates are still widely used in many languages, but rarely in english. One notable exception being condenser microphones, also called capacitor microphones.
Measuring The Charge
How can you measure how much charge is stored in a capacitor? Every cap is made to hold a specific amount of capacitance. This is measured in Farads, after the english chemist Michael Faraday. One Farad will hold a ton of electrical charge, you’ll typically see capacitors measured in picofarads or microfarads. Here’s a helpful chart that shows how these measurements break: down:
Now, to figure out how much charge a capacitor is currently storing you need this equation:
Q = CV
In this equation, the total charge is represented by (Q), and the relationship of that charge can be found by multiplying a capacitor’s capacitance (C), and the voltage applied to it (V). One thing to note here, the capacitance of a capacitor has a direct relationship to its voltage. So, the more you increase or decrease the voltage source in a circuit, the charge that your capacitor will have will increase or decrease rapidly.
The factors to be looked at before choosing a capacitor:
- Stability: The value of the capacitor changes with time and temperature.
- Cost: It should be economical.
- Precision: +/- 20% is not common.
- Leakage: Dielectric will have some resistance and will leak for DC.
- The Target PF and current power factor at site.
- The average & maximum demand in KVA or KW at the proposed site of installation.
- Nature of load of the site.
- The availability of space at the site of installation, power cables, etc.
General uses of Capacitors
- It is used for smoothing in power supplies when required to convert the signal from AC to DC.
- Signal coupling and decoupling as a capacitor coupling.
- It is used for electrical power factor correction.
- In radio systems, an LC oscillator is connected for tuning to the desired frequency.
- Used for the fixed discharging and charging time of the capacitors.
- For Storing Energy.
- It allows an AC current to pass and blocks DC current in circuits.
How Capacitor Works?
First, we can note that a metal typically has an equal amount of positively and negatively charged particles, which means it’s electrically neutral.
If we connect a power source or a battery to the metal plates of the capacitor, a current will try to flow, or the electrons from the plate connected to the positive lead of the battery will start moving to the plate connected to the negative lead of the battery. However, because of the dielectric between the plates, the electrons won’t be able to pass through the capacitor, so they will start accumulating on the plate.
If we connect a power source or a battery to the metal plates of the capacitor, a current will try to flow, or the electrons from the plate connected to the positive lead of the battery will start moving to the plate connected to the negative lead of the battery. However, because of the dielectric between the plates, the electrons won’t be able to pass through the capacitor, so they will start accumulating on the plate.
After a certain number of electrons accumulated on the plate, the battery will have insufficient energy to push any new electronics to enter the plate because of the repulsion of those electrons already present there.
At this point, the capacitor is fully charged. The first plate has developed a net negative charge, and the second plate has developed an equal net positive charge, creating an electric field with an attractive force between them which holds the charge of the capacitor.
Capacitor Dielectric Working Principle
Let’s look at how the dielectric can increase the capacitance of the capacitor. A dielectric contains molecules that are polar which means that they can change their orientation based on the charges on the two plates. So, the molecules align themselves with the electric field in such a way enabling more electrons to be attracted to the negative plate, while repelling more electrons out of the positive plate.
So, once the capacitor is fully charged, if we remove the battery, it will hold the electric charge for a long time, acting as energy storage.
Now, if we shorten the two ends of the capacitor through a load, a current will start flowing through the load. The accumulated electrons from the first plate will start moving to the second plate, until both plates become back again electrically neutral.