What is a Capacitor - Definition
The capacitor is an electric component that has the ability to store energy in the form of electrical charges that creates a potential difference, which is a static voltage, much like a small rechargeable battery.
The most basic design of a capacitor consists of two parallel conductors (Metallic plate), separated with a dielectric material. When a voltage source is attached across the capacitor, the capacitor plate gets charged up. The metallic plate attached to the positive terminal will be positively charged, and the plate attached to the negative terminal will be negatively charged.
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Capacitor Symbols
Types of Capacitors
Film Capacitors: Film capacitors are the ones that use plastic film as the dielectric medium. They are available in nearly any value and voltages up to 1500 volts. They range from 10% to 0.01% in any tolerance. Additionally, film condensers arrive in a combination of shapes and case styles. There are two types of film condensers, radial type lead, and axial type lead.
Ceramic Capacitors: Ceramic capacitors are the ones that use ceramic as the dielectric material. It is used in high-frequency circuits such as audio to RF. In ceramic capacitors, one can develop both high capacitance and low capacitance by altering the thickness of the ceramic disc.
Electrolytic Capacitors: Electrolytic capacitors are the ones that use the oxide layer as the dielectric material. It has a wide tolerance capacity. There are mainly two types of electrolytic capacitors, tantalum, and aluminum. They are available with working voltages of up to approximately 500V, but the maximum capacitance values are not available at high voltage, and higher temperature units are available but are rare.
Variable Capacitor: Variable capacitors mostly use air as the dielectric medium. A Variable Capacitor is one whose capacitance can be mechanically adjusted several times. For example, this form of the capacitor is used to set the resonance frequency in LC circuits to change the radio to match impedance in antenna tuner devices.
Define the Capacitance of a Capacitor
The accumulation of charges in the conductors causes a potential difference across the capacitor. The amount of charge accumulated is called the charge holding capacity of the capacitor. This charge holding capacity is what is known as capacitance. The accumulated charge in the capacitor is directly proportional to the voltage developed across the capacitor:
Q ∝V
Q = C/V
C = Q/V
C is the constant of proportionality, also called the capacitance of a capacitor. The unit of capacitance is Farad(F) - 1 coulomb per volt.
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The value of capacitance depends upon the physical features, area of the capacitor plates ‘A’, distance between the plates ‘d’, and the permittivity of the dielectric medium ‘ε’.
\[C = \varepsilon \times \frac{A}{d}\]
Energy of Capacitor
The energy is stored in joules and is equal to half of the capacitance times the square of the capacitor’s voltage.
\[E = C \times \frac{V^2}{2}\]
Capacitor in Series
The total capacitance of the capacitors connected in series C1, C2, C3,.. :
\[\frac{1}{C_{Total}}\] = \[\frac{1}{C_{1}}\] + \[\frac{1}{C_{2}}\] + \[\frac{1}{C_{3}}\] + …
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Capacitor in Parallel
The total capacitance of the capacitors connected in parallel C1, C2, C3,.. :
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CTotal = C1+C2+C3+...
Factors affecting Capacitance
Surface Area: The surface area of the two plates affects the capacitance value. Higher the value of the surface area, the higher the capacitance.
Distance: The distance between the plates affects the value of the capacitance. Lower the value of distance, the higher the capacitance.
Dielectric Medium: The type of material separating the two plates called "the dielectric." The higher the dielectric's permittivity, the higher the capacitance value.
Uses of a Capacitor
The capacitors have both electrical and electronic applications. They are used for several things such as filters, energy storage systems, engine starters, signal processing devices, etc.
Capacitors are used for storing energy, which can be used by the device for temporary power outages whenever they need additional power.
Capacitors are used for blocking DC current after getting fully charged and yet allow the AC current to pass through the circuit of a circuit.
Capacitors are used as sensor for several things like measuring humidity, fuel levels, mechanical strain, etc.
Capacitors can be used in a time-dependent circuit. This could be connected to any LED or loudspeaker system, and it’s likely that any flashing light/regular beeping uses a timing capacitor.
Fun Facts
Capacitors with high capacitance are made up of material with high dielectric constant.
A Capacitor can take up and temporarily store energy from a circuit. Then, the capacitor will return the energy to the circuit later.
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FAQs on Capacitor and Capacitance
1. Find the expression for the capacitance of a parallel plate capacitor having a surface area of the plate ‘A’ and distance between the plates is d?
Suppose there are two parallel plates 1 and 2. The plate 1 is given with a charge +q (positive). Due to induction, -q (negative) charge is induced on the inner section of plate 2 and +q on the outer surface, but since it is earthed, it will go into the earth. Let the surface charge density of charge on each plate is ρ. The intensity of the electric field at a point between the plates is ρ/ε0.
\[\rho = \frac{q}{A}\]
\[E = \frac{q}{\varepsilon 0A}\] (where ε0 is the permittivity of the material)
Let the potential difference between the two plates be V.
E = V/d
\[V = \frac{qD}{\varepsilon 0A}\]
Substituting the values, we get capacitance as follows:
\[C = \frac{A\varepsilon 0}{d}\]
The unit of capacitance is Farad, after the scientist Michael Faraday.
2. What is a variable capacitor?
Variable capacitors use air as the dielectric medium. It consists of interwoven sets of metal plates in which one is fixed, and the other is variable. The capacitance values of these capacitors may vary from 10pF to 500pF. This type of capacitor enables a change of its capacitance values, either "Mechanically" or "Electrically." Instead of determining values during manufacturing like Fixed Capacitors, certain ranges of values are given in Variable Capacitors. For example, this form of the capacitor is used to set the resonance frequency in LC (inductance-capacitance) circuits to change the radio to match impedance in antenna tuner devices.
3. What are the applications of capacitors?
Capacitor is an electrical component that can store electricity in a static form, like a temporary battery. They are widely used in both electrical and electronic sectors. It is found in different electrical gadgets such as, camera, UPS (Uninterrupted Power Supply) that are connected to the computers; diverse types of motors such as in car engines, in electronic IC chips, capacitors are also used in ceiling fan motors where the torque of the fan motor is compromised if the capacitor is faulty.
4. What governs the choice of dielectric material within a capacitor?
The dielectric material separates the two parallel metal plates within a capacitor. The choice of dielectric medium depends on (a) the amount of electrical charge to be stored, (b) the period of retaining the electrical charge and (c) permittivity of materials. While choosing the dielectric medium, dielectric constant of varied materials is considered, where materials with higher values can store more electrical energy. Some of the commonly used dielectric media are- air (permittivity is 1), aluminum oxide (permittivity 8.5), Barium Strontium titanate (permittivity 500).
5. How to derive the energy of a capacitor in terms of current and voltage?
The energy stored in a capacitor is represented as 0.5CV^2, where
C= capacitance and V= voltage. The term 0.5 represents an average value of the energy. From the theory, electric charge is represented as Q=CV, that is we can write the average energy stored in a capacitor= 0.5(CV)V= 0.5 QV. Again, charge, Q can be expressed as the magnitude of electric current, I, flown over time t. That is, Q = It. Therefore, the average energy stored in a capacitor becomes 0.5 (It)V.
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