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PASSIVE DEVICES These are electronic devices which are not capable of having power gain, they cannot amplify signals For example -Resistor -capacitor -inductors -Transformers 1.Resistors These are passive electrical devices which limit ,regulates ,reduces the flow of electric current in an electronic circuit .The resistor’s ability to reduce the current is called RESISTANCE, and is measured in units of ohms(symbol Ω) Resistor images CLASSIFICATION OF RESISTORS Resistors can be classified into Various categories based on several factors; Classification Based On Composition : On the basis of the composition of the resistor the resistors can be classified as: 1. Carbon Composition: These types of resistors are made by a composition of Carbon Particles which are hold together by a binding resign. The proportion of carbon particles and resign used determines the value of the resistor. At both ends of the composition a Metal Cap with a small rod of tin is attached to solder it or use it in circuits , then the whole package is enclosed in a plastic case to prevent moisture and reaction with air. These types of resistors normally produces noise in circuit due to electron passing through one carbon particle to another , thus these types or resistors are not used in critical circuits although they are cheap. 2. Carbon Deposition: The resistor which is made by depositing a thin layer of carbon around a ceramic rod is called Carbon Deposition resistor. They are made by heating a ceramic rod inside a flask of methane and depositing the carbon around it by using Glass Cracking process. The value of resistor is determined by the amount of carbon deposited around the ceramic rod. 3. High Voltage Ink Film: These types of resistors are made by coating a special resistive ink in a helical band above a ceramic base. These resistors can withstand very high voltage of up to one thousands of kilo voltages and usually have high resistance too ranging from on kilo ohms to one hundred thousand mega ohms. 4. Metal Film: Metal film resistors are made by depositing vaporized metal in vacuum on a ceramic core rod. these types of resistors are very reliable , have high tolerance and also have high temperature coefficient. These types of resistors are costlier compared to other but are used in critical systems. 5. Metal Glaze: Metal Glaze resistors are made up of glass and metal which is mixed and applied as a thick films to a ceramic substrate and then fired to form a film 6. Ceramic Metal: These types of resistor are made by firing certain metals blended with ceramics on a ceramic substrate. The proportion of the mixture in the blended ceramic and metal determines the value of the resistor. These type of resistors are very stable and also have accurate resistance. Based on Resistor’s Value: Based on the resistance value of the resistor the resistors can be classified into following group: 1. Fixed Value Resistor Fixed value resistors are those types of resistors whose value is fixed already while manufacturing and cannot be changed during it’s usage. Fixed Value Resistor 2. Variable Resistor or Potentiometer : Variable Resistors or Potentiometers are those types of resistors whose Value can be changed during it’s usage. Variable Resistors These types of resistor usually contains a shaft which can be rotated or moved by hand or a screw driver to change it’s value in between a fixed range for example. 0 Kilo Ohms to 20 Kilo Ohms. 3. Package Resistor : These types of resistor is a resistor which contains a package which contains two or more resistors inside it. Package Type Resistor It have many terminals and the resistor’s resistance can be chosen by using any two terminals among the available terminals or can also be used as an resistor array for various purposes. Based on Conductive properties of Resistor: Based on the conductive properties of a resistor resistors can be classified as: 1. Linear Resistor: A linear resistor is the type of resistor whose resistance remains constant with increase in the potential difference or voltage applied to it. The V-I characteristics of such resistor is a straight line or in other words these types of resistors follows Ohm’s Law very strictly. Its Outstanding characteristic is the very high surface temperature,which makes it capable of high power dissipation. 2. Non Linear Resistor: Non-Linear Resistor are those types of resistors in which the Current passed through it is not exactly directly proportional to the Potential Difference applied to it. These types of resistors have non-liner V-I characteristics and does not strictly follows ohm’s Law.For example photo resistors LINEAR RESISTORS: Types of Linear Resistors (i)Fixed Resistors: This Is a Resistor which is set to have a specific value of resistance, it cannot be changed. Fixed resistors have several uses. They are used in series with a capacitor to control time relay, Fixed resistors can act as protective devices Ie. Protect other component such as LED from damage by too much current, They can divide voltage between different parts of the circuit(potential divider) Fixed Resistors are also categories in two groups (a)Leaded Resistors Carbon film resistors Carbon film resistors are not expensive in their production,they also make some sort of noise as they operate Metal film resistor Nature of the materials making it make it to have higher accuracy than carbon film, it is used when higher tolerance is required Wire Wound: Wire wound resistor are made by winding a metal wire around a ceramic core. The metal wire is an alloy of various metals based on the characteristics and resistance of the resistor required. These types of resistor have high stability and can also withstand high powers but are usually bulkier compared to other types of resistors (b)surface Mount (SMT) Assembly In this category we have Thin film Resistors and Thick film resistors (ii)Variable Resistors This is a resistor which has several adjustable values of resistance, Variable Resistors are useful for the following -adjustable gain of an Amplifier -adjustable cutoff frequency of an RC Filter -change the brightness of an LED -making measurements with a Wheatstone Bridge -adjusting the sensitivity of sensors wired in series/parallel to the variable resistor Typical Application Of Variable Resistors (i)The Light Dimmer The light dimmer is a other application of variable resistors being put to work. Light dimmers are commonly found in houses and the function of a light dimmer is to change the brightness of the bulbs, that are connected to the circuit, that has the dimmer in it. The dimmer does this by controlling the amount of volts specifically the watts outage to the bulbs. As the more volts are allowed to enter the bulbs the brighter they will be and vice versa. (ii)The Radio The radio you have either in your car or your home or even over your shoulder, this device has variable resistors. You may not see it but behind those knobs for volume is actually a Variable Resistor at work. As the radio is the control center for your sound system, it controls how much volts is being outputted to your speakers. The more volts being inputted into your speakers causes it to be louder, and when volts is less, it becomes quieter Types of Variable Resistors (a)Linear variable Resistor For this Type of variable resistor,there is a linear relationship between the resistance and the position around the track ie.For every degree around its travel, the resistance will vary by the same amount.Virtually all present potentiometer are of linear type,but not all adjustable ones are. (b)Non linear variable Resistor For this Type of variable resistor, there is aNon linear relationship between the resistance and the position around the track ie.For every degree around its travel, the resistance will vary by different amount NON-LINEAR RESISTORS (a)Photoresistor(Light Dependent Resistor)ie cadmium sulphide cells Is a light controlled variable resistor,Its resistance tends to decrease with increasing incident light intensity.APhotoresistor is made of a high resistance semi conductor.In the dark,aphotoresistor can have a resistance as high as a few megaohms while in the light, a photoresistor can have a resistance as low as a few hundreds ohms.Graph showing how resistance varies with light intensity in photoresistors Appied in many devices such as Street lights,outdoorclocks,alarmdevices,solar street lamps,camera light meters,clock radios Application on Street lights Most street lights have Photocells that detect if light is needed. These photocells have light-sensitive sensors which responds to the amount of light detected. When the light is too low, such as at night, the sensor tells the computing unit within the streetlight to activate the flow of electricity. Electricity is normally sent through a high intensity discharge lamp which will then emit light through the arc of the two electrodes. When the photocell detects that there is too much light, it will deactivate the streetlight. Electricity is normally sent through a high intensity discharge lamp which will then emit light through the arc of the two electrodes. A highintensity discharge lamp emits light by an arc of electricity created between two electrodes. The electrodes are in a transparent tube filled with gas and metal salts. The electrical arc generates heat, which works with the gas and metal to create light-emitting plasma. (b)Thermistor These are temperature dependent resistor,there are of two type POSITIVE TEMPERATURE COEFFFIENT(PTC) RESISTORS and NEGATIVE TEMPERATURE COEFFICIENT(NTC) RESISTORS Positive temperature coefficient resistors are those resistors whose resistance increase with increase of temperature Negative temperature coefficient resistors are those resistors whose resistance decrease with increase of temperature. Graph showing how resistance varies with temperature In PTC and NTC resistors (c)Voltage dependent resistor These are resistors whose resistance vary with voltage There are of two types (i)Type I:The resistance increase with increase in voltage (ii)Type II:The resistance decrease with increase in voltage Coding Of Resistors Inorder for values of different resistance of resistors to be known several means are used (i)colour codes on the body of the resistor (ii)Numerical codes/Label on the body of the resistor (I)Colour Codes Resistance value is coded in 4,5 or 6 colourbands,as shown in the figure below (II)Numericalcodes Printed on Resistor Surface The resistor printed numerical codes use the following letters -R=Ohms -K=Kilo Ohms -M=Mega Ohms For example 220R=220Ω, 1R2=1.2Ω, 4M7=4.7MΩ Tolerance can be represented by letters or numbers,incase letters are used ,the following shows letter codes for tolerance F=±1% ,G=±2% ,J=±5% ,K=±10% ,M=±20% .For example R33F Meaning 0.33Ω ± CAPACITORS. These are passive two terminal electrical component which are capable of storing electric charge Capacitor vary widely, but all contain at least two metal plate separated by dielectric(i.e. insulator).Originally capacitor where known as condenser. The ability of a capacitor to store electric energy in form of electric charges is known as the capa of the capacitor. Capacitance is expressed as the ratio of electric charges(Q) on each conductor to potential difference(V) between them. C=Q/V. Where by C-capacitance of a capacitor. The SI unit of capacitance of a capacitor is Farad(F) which is equal to one coulomb per volt. Typ capacitance values range from 1pF (10-12 F) to about 1mF(10-3 F). Symbol of a capacitor are Variable determination of Capacitance. There are three basic factor of capacitor construction affecting the capacitance of a capacitor crea PLATE AREA: If all factors being equal, the greater the surface area of the plate the greater the capacitance of a capacitor; less plate area less the capacitance. PLATE SPACING: If all factors being equal, further plate spacing gives less capacitance; close spacing gives greater capacitance. "Relative" permittivity means the permittivity of a material, relative to that of a pure vacuum. The greater the number, the greater the permittivity of the material. Glass, for instance, with a relative permittivity of 7, has seven times the permittivity of a pure vacuum, and consequently will allow for the establishment of an electric field flux seven times stronger than that of a vacuum, all other factors being equal. The following is a table substances: listing the relative permittivities (also known as the "dielectric constant") of various common Relative permittivity (dielectric constant) Vacuum ------------------------- 1.0000 Air ---------------------------- 1.0006 PTFE, FEP ("Teflon") ----------- 2.0 Polypropylene ------------------ 2.20 to 2.28 ABS resin ---------------------- 2.4 to 3.2 Polystyrene -------------------- 2.45 to 4.0 Waxed paper -------------------- 2.5 Transformer oil ---------------- 2.5 to 4 Hard Rubber -------------------- 2.5 to 4.80 Wood (Oak) --------------------- 3.3 Silicones ---------------------- 3.4 to 4.3 Bakelite ----------------------- 3.5 to 6.0 Quartz, fused ------------------ 3.8 Wood (Maple) ------------------- 4.4 Glass -------------------------- 4.9 to 7.5 Castor oil --------------------- 5.0 Wood (Birch) ------------------- 5.2 Mica, muscovite ---------------- 5.0 to 8.7 Glass-bonded mica -------------- 6.3 to 9.3 Porcelain, Steatite ------------ 6.5 Alumina ------------------------ 8.0 to 10.0 Distilled water ---------------- 80.0 Barium-strontium-titanite ------ 7500 Construction of capacitors. Capacitor consist basically of at least two metal plate separated with electric insulating material called dielectric. Example of dielectric materials are glass, mica, paper, plastic, vacuum, ceramic e.t.c Unlike resistance, capacitor does not dissipate energy. In steady capacitor store energy in form of electrostatic field between its plate. When potential difference is applied across the conductors, an electric field is developed across the dielectric, causing positive charge(+Q) to collect on one plate and negative charge(-Q) on other plate. If a battery has been attached to a capacitor for some sufficient amount of time, no current can flow through the capacitor. However if alternating voltage is applied across the leads of the capacitor, a displacement current can flow. Classification of Capacitors. Capacitors are classified depending on the dielectric materials used to make it (i)Ceramic capacitor. Is a fixed value capacitor in which ceramic material act as dielectric. It is constructed using two or more alternating layer of ceramic and a metal layer acting as electrode. The advantage of using Ceramic capacitor over other type of capacitor. 1. Ceramic capacitor has got low capacitance,generally ceramic capacitor has less than 1 microfarad.Ifelectronic designer need a capacitor with value more than that,he will need to avoid ceramic material and use tantalum or aluminium electrolyte material. 2. Ceramic capacitor can withstand very high voltage than other dielectric material.like plastic or aluminium oxide.This is becouse ceramic material has very high breakdown voltage. Ceramic capacitor has no polarity,so they work well in either AC or DC circuit. Plastic Foil capacitor. These are capacitor insulating plastic film as dielectric. They are made out Of pieces of plastic film covered with metal electrodes,with terminals attached and then encapsulated.In general,film capacitor are not polarized,so the two terminal are interchanged. Mica capacitor. These are capacitors which are made of mica dielectrics.They are one of the oldest materials used in capacitor construction.Mica capacitors they characterized with high stability,high precision and they are one of the reliable capacitors. Electrolytic Capacitors. The electrolytic capacitor consist of essentially of two electrode immersed in electrolyte with a film that constitute the dielectric of one or both.The dielectric film is formed by applying a potential between electrode in unilateral having high resistance in one direction and being conductive in the other.These capacitor are polarized so when using one must observe its terminals. APPLICATION OF CAPACITOR. Capacitor are widely used in electronic circuit for blocking dirent current while allowing alternating . In reasonate circuit,capacitor are used to tune radio to a particular frequency In electric power transmission system,capacitor are used to stabilize voltage and power flow In analogue filter,capacitor are used to smooth the output of power of power supply. NDUCTOR DEFINITION: Inductor is a passive electronical component that stores energy in the form of magnetic field. OR Inductor is a two terminal passive electronic device which resist change in current passing through it. It consists of wires wound in the coil ,when current flows through it energy is stored temporally in magnetic field in the coil. This is the symbol for inductor.. When current changes causes changes in magnetic field which induces an emf in the coil according to Faraday’s laws of electromagnetic induction which states that “whenever there is a change in magnetic flux linking a coil an induced emf is produced”.Emf induced opposes the current produces it.Ø Inductor is characterized by its inductance measured in Henry(H). INDUCTANCE is resistance offered to the electric current by inductor.Inductance is determined by how much magnetic flux is linking the coil,in which inductance is propotional to the change in magnetic flux in the circuit. ie.. L=dØ/di CLASSIFICATION OF INDUCTOR There are many different types of inductor,all differ in size,core material,type of winding..etc CLASSIFICATION OF INDUCTOR BASED ON THEIR VALUES Depending on the value,inductor are classified as.. 1)fixed inductor 2) variable inductor. The number of turns of the fixed coil remain the same,this type is like resistor in shape and can be distinguished by the fact that the first colour band in the fixed inductor is always silver. They are usually used in electronic equipments like radios,communication apparatus,electronic testing equipments..etc. (eg.of variable inductor) (fixed inductor) CLASSIFICATION OF INDUCTOR DUE TO NATURE OF CORE. Core or heart of inductor is the main part of inductor.The following are different types of inductors according to to he nature of the core it has.. 1)Ferromagnetic core/Iron core 2)Air core 3)Toroidai core 4)Laminated core 5)Powered iron core FERROMAGNETIC(IRON) CORE INDUCTOR These are types of inductor that consists of ferrite or iron material in manufacturing for increasing the inductance.Due to high magnetic permeability of these materials,inductance can be increased in response in increasing of magnetic field.At high frequencies it suffers from core loss,energy loss,that happens in ferromagnetic cores. AIR CORE INDUCTOR This is the type of inductor in which there is no any solid exists in the coil.Also,the coil that wounds on nonmagnetic materials such as plastic and ceramic are considered as air cored.The main advantage of this is that at high magnetic field strength they have minimal signal loss.On the other side it requires bigger number of turns so that it can produce the same inductance as the solid cored inductor would have produced. TOROIDAL CORE INDUCTOR Toroidal inductor constructs ring-formed magnetic core that characterized by its magnetic with high permeability material like iron powder,for which the wire wounded to get inductor. It works nicely in AC electronic circuit’s application.The main advantage of this type is due to its symmetry that it has minimum loss in magnetic flux therefore it radiates less electromagnetic interference to near circuit or devices. (toroidal inductor) LAMINATED CORED INDUCTOR It’s the kind of inductor which is more suitable in transformer application.This form typified by it is stacks with thin steel sheet,on top of each designed to be parallel to the magnetic field covered with insulating paint on the surface commonly on oxide finish,It aims to preempt the eddy currents between steel sheet of the stacks so that the current keeps flowing through its sheet and minimizing loop area for which it leads greaty decrease of the energy loss.Laminated core inductor is also a low frequency inductor. (laminated core) POWERED IRON INDUCTOR This is constructed by using magnetic materials that is characterized by it is distrubuted air gaps.This gives advantage to the core to store a high level of energy compared to other types.In addition,a very good inductance stability is gained with losses in eddy current and hysteresis.Morever it has the lowest cost alternative. (powered iron core) FACTORS AFFECTING INDUCTOR Inductance of an inductor is affected by a number of factors,these includes the following.. a)Inductor’s actual size/coil area b)The type and size of the core material used within the inductor c)How the coil is wound For example an inductor with a greater number of wire turns will generate a greater magnetic field force,also a greater coil area represents less opposition to a magnetic field flux,thus resulting in a higher inductance and vice versa in an inductor with smaller coil. APPLICATION OF INDUCTOR There is a lot of application due to a big variety of inductor.Generally inductor are very suitable for radio frequency,suppressing noise,signals,isolation and for high power application. More application are such as a)Energy storage b)Sensors c)Transformers d)Filters e)Motors ENERGY STORAGE Like capacitors,inductor s can be used in energy storage.Unlike capacitors,inductors have a severe limitation on how long they can store energy since the energy is stored in a magnetic field which collapse quickly once power is removed.The main use for inductor s as energy storage is in switch-mode power supplies,like the power in PC. SENSORS Inductors can be used to sense magnetic fields or the presence of magnetically permeable material from distance.INDUCTIVE SENSORS are used at nearly every intersection with a traffic light to detect the amount of traffic and adjust the signal accordingly.These sensors works exceptionally well for cars and trucks,but some motorcycles and other vehicles do not have enough of signature to be detected by the sensors without a little extra boost by adding h3 magnet to the bottom of the vehicle.Inductive sensors are limited in two major ways such as 1)The object to be sensed must be magnetic and induce the current in a sensor. OR 2).The sensor must be powered to detect the presence of materials that interact with magnetic field. This limits the application of inductive sensors and has major impacts on design that use them. TRANSFORMER Combining inductors that have a shared magnetic path will form a transformer .The transformer is a fundamental component of national electric grids and found in many power supplies as well to increase or decrease voltages to a desired level. Since magnetic field are created by a change in current, the faster the current change (increase in frequency) the more effective a transformer operates. FILTERS Inductors are used extensively with capacitors and resistors to create filters for analog circuits and in signal processing.Alone,an inductor as a low-pass filter,since the impedence of an inductor increases as the frequency of signal increases.When combined with a capacitor,whose impedence decreases as the frequency of a signal increases,a notched filter can be made that only allows a certain frequency range topath through.By combining capacitors,inductors and resistors in a number of way advanced filter topologies can be created for a number of application. Filters are used in most electronics,although capacitors are often used rather than inductors when possible since they are smaller and cheaper. MOTORS Normally inductors are in a fixed position and not allowed to move to align themselves with any nearby magnetic field.INDUCTIVE MOTORS leverage the magnetic force applied to inductors to turn electrical energy in to mechanical energy.inductive motors are designed so that the rotating magnetic field is created in time with AC input.Since the speed of rotating magnetic field is controlled by the input frequency. The biggest advantage of inductive motor over other design is that no electrical contact is required between the rotor and the motor which makes inductive motors very robust and reliable. TRANSFORMER DEFINITION: Transformer is the electrical device that transfers energy between two circuits through electromagnetic induction. Transformer consist of two windings of wire wounded around a laminated iron core. There is primary and secondary windings. Where a primary coil or winding is receiving the input power while secondary windings gives the output power. A circuit symbol of transformer An AC flowing through the primary coil of transformer generates the varying electromagnetic field in its surroundings which causes the variation of magnetic flux in the core of transformer. By the principle of mutual induction an electromotive force is induced in the secondary coil of transformer. The Emf induced is given as output voltage across the output terminals of transformer. CLASSIFICATION OF TRANSFORMER: Transformer can be classified according to different factors: 1.BASING ON APPLICATION There is a)Step up transformer b)Step down transformer A. STEP UP TRANSFORMER A step up transformer increases the output voltage while lowering the current. It consist of many number of turns in secondary coil than in primary coil. Hence the output voltage is larger compared to the input voltage. Step up transformer are mainly used for transmission of power from power plants supply to the users like industries, homes e.tc. The generated power is increased so as to reduce the effect of power loss during transmission. B. STEP DOWN TRANSFORMER The step down transformer is having many number of turns in the primary coil with few number of turns in secondary coil, hence the output voltage is lower than input voltage. This kind of transformer are used to lower voltages from power stations to a suitable amount required by users usually 240V for households. Are also found in different electronic devices like T.V, radios and computers. Normally step up and step down transformer depends on each other in applications, the following figure shows how step up and step down transformer works 2.BASING ON EFFICIENCY OF TRANSFORMER Efficiency of transformer is given as the ratio of power output to the power input in transformer. Basing on efficiency transformer is classified into; a)Ideal transformer b)real or practical transformer A.IDEAL TRANSFORMER Ideal transformer is assumed to be 100% efficient basing in the following assumptions; (1)the windings has zero resistance, hence there is no Copper losses and voltage drop across the windings. (2)Flux is confined within the magnetic core, hence the same flux links the input and output windings. This assumption gives the equation of transformer. From Faraday’s law of induction VS=NsdØ/dt Vp= NsdØ/dt Combining the two equations gives; Vs/Vp=Ns/Np Which is the equation of transformer. (3)Permeability of the core is infinitely high. This implies that net magnetomotive force (mmf)is zero, i.e IpNp=IsNs (4)Any load connected across secondary windings of transformer allows energy to flow without loss from primary to secondary circuit. Hence resulting input and output power are equal and given by IpVp=IsVs Where; Np=number of turns in primary coil Vp=voltage in primary coil Ip=current in primary coil Ns=number of turns in secondary coil Vs=number of turns in secondary coil Is=current in secondary coil Hence ideal transformer are considered as perfect transformers. B. REAL TRANSFORMER Is 95% to 99% due to transformer losses like current losses and leakage flux losses. 3.BASING ON PHASES There is (a)Three phase transformer Three phase transformer in both core and shell transformer is made up of three sets of primary and secondary windings each set wound around one leg of iron core assembly. (b)Single phase transformer A single phase transformer where in core type it consist of two limbs the coils are wound on all two limbs while in shell type it has three limbs with the wire wound in only one limb as shown in the diagram. TRANSFORMER LOSSES. Transformer losses are as follows; COPPER LOSSES This arise due to the resistance in the windings which opposes the flow of current in the conductor. The electron motion causes the conductor molecules to move and produce heat energy which is not taken as part of output power. Ie H=I2RT HYSTERISIS LOSS Hysterisis loss occurs due to the process of magnetization and demagnetization of the core of transformer. Whenever magnetic flux is passing the core is magnetized and when current is off the core is not totally demagnetized hence hence the other mmf has to be applied in opposite direction. The mmf applied in transformer is AC for every cycle and due to this reversal there would be extra workdone, hence there will be consumption of energy known as hysteresis loss in transformer. EDDY CURRENT LOSS Eddy current are circulating current within the core in plane normal to the flux. These currents are due to the leakage flux that escape from the core and pass only through one winding. Such leakage flux cause eddy currents in the transformer parts which does not contribute to the outputs therefore dissipated as heat. Eddy current loss is reduced by thinner lamination of the transformer core.