Class 12th Physics Project File (Capacitors) 23-24
- 1. DELHI PUBLIC SCHOOL KALYANPUR SESSION – 2023-24 PHYSICS PROJECT FILE SUBMITTED TO : SUBMITTED BY : MANOJ SHARMA Akshat Singh Chaudhary XII S7 Roll No. 1
- 2. ACKNOWLEDGEMENT I would like to convey my heartfelt thanks to Mr. Manoj Sharma my faculty of Physics who gave his valuable suggestions and guidance for the completion of my project. He helped me to comprehend important details of the project. My project has been successful only because of his able guidance and support. Signature of the Principal Signature of the Subject Teacher
- 3. CONTENTS S.No. TOPIC PAGE NO. 1. COVER PAGE (i) 2. ACKNOWLEDGEMENT (ii) 3. CAPACITORS 4. AMOUNT OF CHARGE Q A CAPCITOR CAN STORE 5. SELF CAPACITANCE 6. CHARGING & DISCHARGING OF A CAPACITOR 7. ENERGY OF A CAPACITOR 8. TYPES OF CAPACITORS 9. USES OF CAPACITORS
- 4. CAPACITORS A capacitor is a device used to store electric charge. Capacitors have applications ranging from filtering static out of radio reception to energy storage in heart defibrillators. Typically, commercial capacitors have two conducting parts close to one another, but not touching. When by terminals are connected to an initially uncharged capacitors, equal amount of positive and negative charge, +Q and –Q, are separated into its two plates. The capacitor remains neutral overall, but we refer to it as storing a charge Q in this circumstance. FIG. (i) A Parallel Plate Capacitor (ii) Electric Field generated in A Parallel Plate 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 figure (ii) given above 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.
- 5. The field is proportional to the charge: E ∝ 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 Fig – Different types of capacitors
- 6. 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 ishaving radius of 20 cm self-capacitance is 22.24pF. For the planet EARTH self-capacitance is 710 µF. Let us assume that the capacitor, which is shown in the figure below in the circuit, is completely discharged. In this circuit the capacitor value is 100 µF and the supply voltage applied to this circuit is 12V. Now the switch which is connected to the capacitor in the circuit is moved to the point A. Then the capacitor starts charging with the charging current I. The charging voltage across the capacitor is equal to the supply voltage when the capacitor is fully charged i.e. VS = VC = 12V. In the case of ideal capacitors the charge remains constant on the capacitor but in the case of general
- 7. capacitors the fully charged capacitors is slowly discharged because of its leakage current. When the switch is moved to the position B, then the capacitor slowly discharges by switching on the lamp which is connected in the circuit. 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 t energy and work. 𝑑𝑊 = 𝑉 𝑑𝑄 𝑑𝑊 = 𝑄/𝐶 𝑑𝑄 After the integration of this equation: 𝑊 = 𝑄2 /2𝐶 𝑊 = (𝐶𝑉)2 /2𝐶 𝑊 = 𝐶𝑉2 2 Finally we get the energy stored in a capacitor is: 𝑊 = 𝐶𝑉2 2 Joules
- 8. Now we calculate the energy stored in a capacitor of capacitance 200 µF which operate with voltage of 12V 𝑊 = 200 × 10−6 × 122 2 = 14.4 𝑚𝐽 FILM CAPACITORS 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 valueand 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 aluminum 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. CERAMIC CAPACITORS Ceramic capacitors are used in high frequencycircuits 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.
- 9. Ceramic capacitors are made by coating two sides of as mall 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 manythousands of volts. Ceramics are inexpensive to manufacture and they come with several dielectrics types. ELECTROLYTIC CAPACITORS There are two types of electrolytic capacitor, Tantalum and Aluminum. It is most prevalently used capacitors which havea wide tolerance capacity. Electrolytic capacitors are available with workingvoltages up to about 500V. Tantalums capacitors have ordinarily better exhibition, higher value. The dielectric properties of tantalum oxide is much superior to those of aluminum oxide. It has an easier leakage current and better capacitance strength which makes them suitable for obstructing, decoupling, filtering applications. The thickness of the aluminum oxide film and heightened breakdown voltage gives the capacitor exceptionally elevated capacitance values for their size.
- 10. 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
- 11. 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.