Capacitor and Its Working Investigatory
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Introduction
A capacitor is an electronic component used to store electrical energy temporarily in an electric field. It consists of two conductive plates separated by an insulating material called a dielectric. When a voltage difference is applied across the plates, electric charge accumulates on them, creating an electric field between the plates. Capacitors are widely used in electronic circuits for various purposes such as filtering, smoothing power supply voltages, coupling signals between stages, and storing energy in pulse circuits. They come in various types and sizes, each suitable for different applications based on factors like capacitance value, voltage rating, and frequency response.
Structure of Capacitors
The internal structure of a capacitor consists of two main components: conductive plates and a dielectric material. These plates, typically made from materials like aluminium, tantalum, or ceramic, are placed parallel to each other with a small gap in between. The dielectric material, which could be paper, ceramic, plastic film, or oxide layers, serves as an insulator between the plates. This dielectric material determines the capacitor’s capacitance and other electrical characteristics. The conductive plates are connected to lead wires or terminals that extend outside the capacitor, allowing it to be integrated into electrical circuits. The entire assembly is often enclosed in a protective casing made of materials like plastic or epoxy resin to safeguard it from physical damage and environmental factors. This basic structure enables capacitors to store and release electrical energy efficiently, making them indispensable in various applications across electronics, from filtering and signal processing to energy storage and power factor correction.
Charge Stored in Capacitor
The amount of charge Q a capacitor can store depends on two major factors the voltage applied and the capacitor’s physical characteristics, such as its size. In below given figure each electric field line starts on an individual positive and ends on a negative one, so that there will more field lines if there is more charge. The electric field strength is, thus, directly proportional to Q.
The field is proportional to the charge: V ∝ Q
We know that V= Ed
So, V ∝ E
Hence, V ∝ Q
Removing sign of proportionality, we get Q= CV
Where C = Capacitance of the Parallel Plate Capacitor.
The unit of capacitance is the farad (F), named after Michael Faraday (1791-1867), an English scientist who contributed to the fields of electromagnetism and electrochemistry. Since capacitance is charge per unit voltage, we see that a farad is a coulomb per volt. A 1-farad capacitor would be able to store 1 coulomb with the application of only 1 volt. is, thus a very large capacitance. Typical capacitors range from fractions of a picofarad to millifarads.
1C/1V= F
Self-Capacitance
Self-capacitance property is related to the capacitors especially to the isolated conductor to raise its potential difference to one volt. Generally normal conductors will have mutual capacitance. This is also measured in the S.I unit i.e. Farads.
The Self-capacitance of a conducting sphere which has the radius ‘R’ is given by
C= 4πε0R
Self-capacitance values of some standard devices are given below.
- For the top plate of a van de Graff generator which is having radius of 20 cm self-capacitance is 22.24 pF.
- For the planet EARTH self-capacitance is 710 µF.
Charging and Discharging of Capacitor
The charging and discharging of a capacitor are fundamental processes in electronics. When charging a capacitor, it begins with no voltage across its plates and is connected to a voltage source, typically through a resistor. Initially, current flows rapidly as the capacitor behaves like a short circuit, gradually accumulating charge and increasing its voltage. The relationship between the capacitor voltage, the source voltage, and time is governed by an exponential function determined by the RC time constant of the circuit.
In contrast, discharging occurs when a charged capacitor is connected across a resistor or short-circuited, allowing stored charge to flow through the resistor. The capacitor’s voltage decreases exponentially over time as it discharges, following a similar exponential function dependent on the initial voltage and the RC time constant. Understanding these processes is crucial in electronics for designing circuits such as filters, timers, and energy storage systems where capacitors play pivotal roles in storing and releasing electrical energy efficiently.
Energy Stored in Capacitor
Energy is the amount of some work against the electro-static field to charge the capacitor fully. In the capacitor at initial stage of charging, the charge Q transferred between the plates from one plate to another plate. This charge either +Q or -Q is interchanged between two plates of a capacitor. After transformation of some charge an electric field is formed between the plates, in that case we need some extra work to charge the capacitor fully. This extra work is called as the energy stored in a capacitor, the energy is measured in the units of Joules (J). Now we see the equations for energy and work.
Types of Capacitors
- Film Capacitor:
- Film Capacitors comprising of a generally expansive group of capacitors with the distinction being in their dielectric properties.
- Film Capacitors are available in almost any value and voltages as high as 1500 volts.
- They come in tolerance from 10% to 0.01%.
- There are two types of film capacitors i.e. Radial lead type & Axial lead type.
- The electrodes of film capacitors may be metalized aluminium or zinc.
- They use polystyrene, polycarbonate or Teflon as their dielectrics.
- It can be used in AC voltage applications, and they have much more stable electrical parameters.
2. Ceramic Capacitors
- Ceramic capacitors are used in high frequency circuits such as audio to RF.
- Ceramic Capacitors are the best choice for high frequency compensation in audio circuits.
- These capacitors are also called as disc capacitors.
- Ceramic capacitors are made by coating two sides of a small porcelain or ceramic disc with silver and are then stacked together to make a capacitor.
- They come in values from a few Pico farads to 1 microfarad.
- The voltage range is from a few volts up to many thousands of volts.
- Ceramics are inexpensive to manufacture and they come with several di-electrics types.
3. Electrolytic Capacitor
- There are two types of electrolytic capacitor, Tantalum and Aluminium.
- It is most prevalently used capacitors which have a wide tolerance capacity.
- Electrolytic capacitors are available with working voltages up to about 500V.
- Tantalums capacitors have ordinarily better exhibition, higher value.
- The dielectric properties of tantalum oxide is much superior to those of aluminium oxide.
- It has an easier leakage current and better capacitance strength which makes them suitable for obstructing, decoupling, filtering applications.
- The thickness of the aluminium oxide film and heightened breakdown voltage gives the capacitor exceptionally elevated capacitance values for their size.
Use of Capacitors
Capacitors are devices which store electrical charge. They are a basic component of electronics and have a host of various applications. The most common use for capacitors is energy storage. Additional uses include power conditioning, signal coupling or decoupling, electronic noise filtering, and remote sensing. Because of its varied applications, capacitors are used in a wide range of industries and have become a vital part of everyday life.
- Capacitors for Energy Storage
Capacitors have been used to store electrical energy since the late 18th century. Benjamin Franklin was the first to coin the phrase “battery” for a series of capacitors in an energy store application. Individual capacitors generally do not hold a great deal of energy, providing only enough power for electronic devices to use during temporary power outages or when they need additional power. For example, large capacitors are included in car audio systems to provide extra power to amplifiers when needed.
- Capacitors for Power Conditioning
One important application of capacitors is the conditioning of power supplies. Capacitors allow AC signals to pass but block DC signals when they are charged. They can effectively split these two signal types, cleaning the supply of power. This effect has been exploited to separate or decouple different parts of electrical circuits to reduce noise which could lead to reduction of efficiency. Capacitors are also used in utility substations to counteract inductive loading introduced by transmission lines.
- Capacitors as Sensors
Capacitors are used as sensors to measure a variety of things, including air humidity, fuel levels and mechanical strain. The capacitance of a device is dependent on its structure. Changes in the structure can be measured as a loss or gain of capacitance. Two aspects of a capacitor are used in sensing applications: the distance between parallel plates and the material between them. The former is used to detect mechanical changes such as acceleration and pressure. Even minute changes in the material between the plates can be enough to alter the capacitance of the device, an effect exploited when sensing air humidity.
- Capacitors for Signal Processing
Capacitors have found increasingly advanced applications in information technology. Dynamic Random Access Memory (DRAM) devices use capacitors to represent binary information as bits. The device reads one value when the capacitor is charged and another when discharged. Charge Coupled Devices (CCDs) use capacitors in an analogue form. Capacitors are also used in conjunction with inductors to tune circuits to particular frequencies, an effect exploited by radio receivers, speakers and analog equalizers.
Major Drawback of Capacitors
Capacitors, while useful components in electrical circuits, do have some drawbacks:
- Limited Energy Storage: Capacitors can store electrical energy, but compared to batteries, they have much lower energy density. This means they can store less total energy for a given size and voltage rating.
- Voltage Limitations: Capacitors have maximum voltage ratings beyond which they can be damaged or fail. Exceeding this voltage can cause breakdown of the dielectric material or even physical damage to the capacitor.
- Leakage Current: All capacitors exhibit some amount of leakage current, which can gradually discharge the capacitor over time. This can be a significant factor in applications where the capacitor needs to retain charge over long periods.
- Temperature Sensitivity: The capacitance value of a capacitor can change with temperature, which may affect the performance of circuits relying on precise capacitance values.
- Frequency Dependence: Capacitors can behave differently at different frequencies due to parasitic effects such as inductance and resistance. This can lead to deviations from ideal behavior, impacting circuit performance in high-frequency applications.
- Size and Cost: Capacitors can take up physical space in a circuit, especially when high capacitance values are needed. Additionally, high-performance capacitors can be relatively expensive compared to other passive components like resistors.
Conclusion
Capacitors are fundamental components in electronic circuits, playing crucial roles such as energy storage, signal filtering, and voltage regulation. They are constructed with two conductive plates separated by a dielectric material, enabling the temporary storage of electrical energy in an electric field. This project has explored their internal structure, operational principles, and various types, illustrating their wide-ranging applications across industries. However, capacitors do have inherent limitations. These include lower energy density compared to batteries, maximum voltage ratings, potential leakage currents, and sensitivity to temperature variations and frequency dependencies. Engineers and designers must carefully consider these factors when selecting capacitors to ensure optimal performance and reliability in electronic systems. Despite these challenges, ongoing advancements in capacitor technology continue to address these limitations, aiming to enhance efficiency and broaden their utility in diverse and evolving technological applications.
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