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. What is the fundamental difference between a capacitor and capacitance?
A capacitor is a physical electronic component designed to store electrical energy. It typically consists of two conductive plates separated by a dielectric material. Capacitance, on the other hand, is the property or ability of a capacitor to store an electric charge. It is a measure of how much charge a capacitor can store per unit of voltage applied across it. In simple terms, a capacitor is the device, and capacitance is its storage capacity.
2. What is the primary role of a capacitor in an electronic circuit?
The primary role of a capacitor is to store electrical energy in an electric field and then release it when needed. This function allows it to be used for various applications, such as:
- Filtering out unwanted noise from power supplies.
- Blocking direct current (DC) while allowing alternating current (AC) to pass.
- Timing circuits (e.g., in oscillators or flash circuits).
- Energy storage for quick-release applications like a camera flash.
3. How is the capacitance of a parallel plate capacitor calculated, and what factors influence it?
The capacitance (C) of a parallel plate capacitor is given by the formula: C = ε(A/d). The value is influenced by three main physical factors:
- A (Area of the plates): Capacitance is directly proportional to the overlapping surface area of the conductive plates. A larger area allows for more charge storage.
- d (Distance between the plates): Capacitance is inversely proportional to the distance separating the plates. A smaller distance results in a stronger electric field and higher capacitance.
- ε (Permittivity of the dielectric): This is a property of the insulating material between the plates. Materials with higher permittivity (dielectric constant) increase the capacitance.
4. What is the difference between connecting capacitors in series and in parallel?
When connecting capacitors, the total capacitance (C_eq) of the circuit changes:
- In Series: The reciprocal of the equivalent capacitance is the sum of the reciprocals of individual capacitances (1/C_eq = 1/C₁ + 1/C₂ + ...). The total capacitance is always less than the smallest individual capacitance. The charge stored on each capacitor is the same.
- In Parallel: The equivalent capacitance is the direct sum of the individual capacitances (C_eq = C₁ + C₂ + ...). The total capacitance increases. The voltage across each capacitor is the same.
5. Why does inserting a dielectric slab between a capacitor's plates increase its capacitance?
When a dielectric material is inserted into the electric field between the capacitor plates, its molecules get polarized. This creates an internal electric field within the dielectric that opposes the main electric field from the charged plates. The net electric field between the plates is reduced. Since potential difference (V) is the product of the electric field and distance (V = Ed), a reduced electric field leads to a lower potential difference for the same amount of charge (Q). As capacitance is defined by C = Q/V, a decrease in V results in an increase in capacitance.
6. How can a capacitor block DC but allow AC to pass?
This behaviour is due to a property called capacitive reactance (X_C), which is inversely proportional to frequency (f).
- For DC (Direct Current), the frequency is zero (f=0). This makes the capacitive reactance infinitely high, effectively acting as an open circuit or a 'block'. A capacitor charges up to the DC voltage and then stops any further current flow.
- For AC (Alternating Current), the frequency is non-zero. The capacitor continuously charges and discharges as the current direction reverses, allowing current to effectively 'pass' through the circuit. The higher the frequency, the lower the reactance and the easier the current flows.
7. What is the key difference between how a capacitor and a battery store energy?
While both store energy, they do so through different mechanisms and for different purposes.
- A capacitor stores energy electrostatically in an electric field between its plates. It can charge and discharge very rapidly, making it ideal for delivering short, high-power bursts (like in a camera flash).
- A battery stores energy chemically through electrochemical reactions. It releases this energy at a much slower, more stable rate over a longer period, making it suitable for providing continuous power to devices.
8. What are the main types of capacitors, and what are their typical applications?
Capacitors are often classified by their dielectric material. Common types include:
- Ceramic Capacitors: Use ceramic as the dielectric. They are small and used for high-frequency applications like in radio frequency (RF) circuits due to their low loss.
- Electrolytic Capacitors: Use an electrolyte to form a very thin oxide layer as the dielectric. They offer high capacitance values and are common in power supply filtering.
- Film Capacitors: Use a thin plastic film as the dielectric. They are known for their stability, making them suitable for audio circuits.
- Variable Capacitors: Use air as the dielectric and have a mechanism to change their capacitance. They are used in tuning circuits for radios.
9. What is the SI unit of capacitance?
The SI unit of capacitance is the Farad (F), named after Michael Faraday. One Farad is defined as the capacitance of a capacitor that stores one coulomb of charge when a potential difference of one volt is applied across it (1 F = 1 Coulomb/Volt). In practice, the Farad is a very large unit, so capacitance is often measured in smaller units like microfarads (μF), nanofarads (nF), or picofarads (pF).
