What is Capacitor – Types, Formula, Symbol
Learn What is Capacitor – Types, Formula, Symbol, How it Works, Unit.
Here we Learn What is Capacitor – Types, Formula, Symbol, How it Works, Unit, Electrolytic Capacitor, Application and Function Explained in Detail.
What is Capacitor?
A capacitor is an electronic component characterized by its capacity to store an electric charge. A capacitor is a passive electrical component that can store energy in the electric field between a pair of conductors (called “plates”).
In simple words, we can say that a capacitor is a device used to store and release electricity, usually as the result of a chemical action. Also referred to as a storage cell, a secondary cell, a condenser or an accumulator. A Leyden Jar was an early example of a capacitor.
Capacitors are another element used to control the flow of charge in a circuit. The name derives from their capacity to store charge, rather like a small battery.
Capacitors consist of two conducting surfaces separated by an insulator; a wire lead is connected to each surface.
What is Capacitor and How Capacitors Work
Capacitor Symbol and Unit
There are two capacitor symbols generally used in electronics. One symbol is for polarized capacitors, and the other is for non-polarized capacitors.
In the above diagram, the symbol with one curved plate represents a Polarized Capacitor. The curved plate represents the cathode (negative) of the capacitor, and the other plate is anode (positive). Sometimes a plus sign is also added to the positive side.
The SI unit of capacitance is farad (Symbol: F). The unit is named after Michael Faraday, the Great English Physicist.
A 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates.
Types of Capacitors
There are several types of capacitors for different applications and functions. Following are the Main and Most Common Types:
1. Ceramic Capacitors
These are non-polarized capacitors made out of two or more alternating layers of ceramic and metal. The ceramic acts as the dielectric and the metal acts as the electrodes.
Ceramic Capacitors are also called “Disc Capacitors.”
A code of 3 Digit is generally printed on the body of this type of capacitors to tell their capacitance in pico-farads. The first two digits represent the value of the capacitor and the third digit represents the number of zeros to be added.
2. Electrolytic Capacitor
These type of capacitors are generally used where large capacitance is needed. Anode of electrolytic capacitors is made of metal and is covered with an oxidized layer used as dielectric. The other electrode can be either wet non-solid or solid electrolyte.
Electrolytic capacitors are polarized. This means that correct polarity must be used when supplying DC voltage to it. In simple words positive lead of the capacitor must be connected with positive terminal and negative plead to the negative terminal. Not doing so will damage the capacitor.
These capacitors are grouped into following 3 Types depending on their dielectric:
- Aluminum electrolytic capacitors.
- Tantalum electrolytic capacitors.
- Niobium electrolytic capacitors.
3. Film Capacitor
These are most common type of capacitor used in electronics.
Film capacitors or plastic film capacitors are non-polarized. Here an insulating plastic film acts as the dielectric. Electrodes of these types of capacitors can be aluminum metal or zinc reactive metal. They are applied on one or both sides of the plastic film thus forming a metallized film capacitor. Sometimes a separate metallic foil is used over the film thus forming a film or foil capacitor.
Film capacitors are available in different shapes and sizes and offer several advantage over paper type capacitors. They are highly reliable, have long life and have less tolerances. They also function well in high temperature environment.
4. Variable Capacitor
These are non-polarized variable capacitance type of capacitors. They have moving and fixed plates to determine the capacitance. They are generally used in Transmitters and Receivers, Transistor Radios etc.
These capacitors are grouped as:
- Tuning capacitors; and
- Trimmer capacitors
How Capacitor Works?
You can imagine a capacitor as two large metal plates separated by air, although in reality they usually consist of thin metal foils or films separated by plastic film or another solid insulator, and rolled up in a compact package. Consider connecting a capacitor across a battery.
As soon as the connection is made, charge flows from the battery terminals, along the wire and onto the plates, positive charge on one plate, negative charge on the other.
Why? The like-sign charges on each terminal want to get away from each other. In addition to that repulsion, there is an attraction to the opposite-sign charge on the other nearby plate. Initially the current is large, because in a sense the charges can not tell immediately that the wire does not really go anywhere, that there is no complete circuit of wire.
The initial current is limited by the resistance of the wires, or perhaps by a real resistor. But as charge builds up on the plates, charge repulsion resists the flow of more charge and the current is reduced. Eventually, the repulsive force from charge on the plate is strong enough to balance the force from charge on the battery terminal, and all current stops.
The existence of the separated charges on the plates means there must be a voltage between the plates, and this voltage be equal to the battery voltage when all current stops. After all, since the points are connected by conductors, they should have the same voltage; even if there is a resistor in the circuit, there is no voltage across the resistor if the current is zero, according to Ohm’s law.
The amount of charge that collects on the plates to produce the voltage is a measure of the value of the capacitor, its capacitance, measured in farads (f). The relationship is C = Q/V , where Q is the charge in Coulombs.
Large capacitors have plates with a large area to hold lots of charge, separated by a small distance, which implies a small voltage. A one farad capacitor is extremely large, and generally we deal with microfarads ( µf ), one millionth of a farad, or picofarads (pf), one trillionth (10-12) of a farad.
Consider the above circuit again. Suppose we cut the wires after all current has stopped flowing. The charge on the plates is now trapped, so there is still a voltage between the terminal wires. The charged capacitor looks somewhat like a battery now.
If we connected a resistor across it, current would flow as the positive and negative charges raced to neutralize each other. Unlike a battery, there is no mechanism to replace the charge on the plates removed by the current, so the voltage drops, the current drops, and finally there is no net charge left and no voltage differences anywhere in the circuit.
The behavior in time of the current, the charge on the plates, and the voltage looks just like the graph above. This curve is an exponential function: exp(-t/RC) . The voltage, current, and charge fall to about 37% of their starting values in a time of R ×C seconds, which is called the characteristic time or the time constant of the circuit.
The RC time constant is a measure of how fast the circuit can respond to changes in conditions, such as attaching the battery across the uncharged capacitors or attaching a resistor across the charged capacitor. The voltage across a capacitor cannot change immediately; it takes time for the charge to flow, especially if a large resistor is opposing that flow. Thus, capacitors are used in a circuit to damp out rapid changes of voltage.
Combinations of Capacitors
Like resistors, capacitors can be joined together in two basic ways: parallel and series.
How to Calculate Capacitance of a Capacitor?
It should be obvious from the physical construction of capacitors that connecting two together in parallel results in a bigger capacitance value. A parallel connection results in bigger capacitor plate area, which means they can hold more charge for the same voltage. Thus, the formula for total capacitance in a parallel circuit is: CT=C1+C2…+Cn.
The same form of equation for resistors in series, which can be confusing unless you think about the physics of what is happening.
The capacitance of a series connection is lower than any capacitor because for a given voltage across the entire group, there will be less charge on each plate. The total capacitance in a series circuit is : CT={1{1C1}+{1C2}…+{1Cn}}.
Again, this is easy to confuse with the formula for parallel resistors, but there is a nice symmetry here.
FAQs: Capacitor and Capacitance
How does a capacitor work?
When a voltage is applied across the two plates of a capacitor, it stores electrical charge on its plates. The stored charge creates an electric field between the plates. The capacitor discharges when the voltage is removed, releasing the stored energy.
What are the different types of capacitors?
There are various types of capacitors, including ceramic, electrolytic, tantalum, film, and paper capacitors. Each type has unique properties and is suitable for specific applications.
What is the unit of capacitance?
The unit of capacitance is the farad (F), named after Michael Faraday. However, capacitors are often measured in smaller units such as microfarads (μF) and picofarads (pF) due to their typically small values.
What are capacitors used for?
Capacitors have numerous applications in electronics, including energy storage, noise filtering, coupling and decoupling, timing circuits, and power factor correction. They are found in electronic devices, power supplies, communication systems, etc.
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