Permanent Magnet and Its Uses

Permanent magnet is a material that has their own magnetic field. It is an object that creates its own persistent magnetic field when it is magnetized. Permanent magnet exists in nature in the form of lodestone, which are used as magnetic compass. The most common magnets in use are the refrigerator magnet, speaker magnet, magnetic mariners compass magnet, ones used in magnetic motors etc. Permanent magnets can also be made artificially by passing strong direct current through an insulated coil of wire in which the material to be magnetized is placed. The materials that can be magnetized which are also strongly attracted to a magnet are called as ferromagnetic materials. These include iron, steel, nickel, cobalt, alloys of rare earth metals, etc.  They are also used for making permanent magnets. Steel is slow to magnetize but retains magnetism for long as it has low susceptibility to magnetism but has high retentiveness.

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Ferromagnetic materials can be divided into:

1. Magnetically soft materials such as annealed iron, that can be magnetized but do not tend to stay magnetized.

2. Magnetically hard materials that tend to stay magnetized always.

Permanent magnets are made from hard ferromagnetic materials such as alnico and ferrite when they are subjected to a special processing in a powerful magnetic field during manufacture for aligning their internal micro crystalline structure, which makes them hard to demagnetize.

Permanent Magnetism

Magnetic materials posses two poles of opposite effect denoted as North and South because of their self orientation to the earth. The poles of the magnet  sustains even when the magnet is cut into two.  The two poles exist just like the electric charges, the positive charge and the negative charge. Similarly the same poles repel each other and opposite poles attract each other. The magnetic flux just like the static electric charge is able to invisibly extend over space and pass through objects such as paper and wood with little effect upon their strength.

Magnetic flux density also called as magnetic B field, is a vector field. The magnetic B field vector at a given point has 2 properties.

1. The direction along the orientation of a compass needle.

2. The magnitude or strength which is proportional to the how strongly the compass needle orients along that direction.

The strength of the magnetic field is given in tesla.

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The magnet's magnetic moment also called as dipole moment, is a vector that denotes the magnet's overall magnetic properties. In a bar magnet the direction of the magnetic moment points from the magnet's South Pole to its North Pole. The magnitude relates to how strong and how farther away these poles are. A magnet produces both its own magnetic field and also responds to magnetic fields. The strength of the magnetic field it produces at any given point is proportional to the magnitude of its magnetic moment. When a magnet is subjected to an external magnetic field produced by another source, it is subjected to a torque tending to orient the magnetic moment parallel to the field. The amount of this torque is proportional to both the magnetic moment and the external field. A magnet may also be subjected to a force driving it in one direction or another according to the positions and orientations of the magnet and the source.

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The Models of Magnetism

Two different models for magnet exist, magnetic pole model and atomic current model.

1. In the magnetic pole model, the magnet is being referred to as having two distinct poles North and South. It is merely a way of referring to the two different ends of a magnet. The magnet does not have distinct North or South particles at the opposing sides. When a bar magnet is broken into two pieces, the result will be two bar magnets each of which has both a North and a South pole.

2. In the atomic model, all the magnetization is due to the effect of microscopic, atomic, circular bound currents or Ampere currents throughout the material. For a uniformly cylindrical bar magnet, the net effect of the microscopic bound current is to make the magnet behave as there is a macroscopic sheet of electric current flowing around the surface with local flow direction parallel to the cylinder axis.

The magnetism of a permanent magnetic field is produced by an electric charge in motion.  The magnetic field of the permanent magnet is the result of the electrons within the atoms of iron spinning uniformly in the same direction.  This kind of uniform spinning of the electrons in the atom is dictated by the electron binding in that material's atoms. So depending upon the atomic structure of the material, only certain types of materials can react to the magnetic fields and only fewer have the ability to permanently sustain a magnetic field.

The overall magnetic behavior of a material can vary depending upon the structure of the material, particularly its electron configuration.

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Different Magnetic Materials

Different types of behaviors have been observed in different materials:

Ferromagnetic and ferrimagnetic materials are attracted to a magnet strongly. These materials can retain magnetization and become magnets. Ferrimagnetic materials include ferrites, magnetite, lodestone etc.

Paramagnetic substances such as platinum, aluminum, and oxygen are weakly attracted to either pole of a magnet. This attraction is hundreds or thousand times weaker than that of the ferromagnetic materials.

Diamagnetic materials those which are repelled by the poles. Diamagnetic materials include carbon, copper, water, and plastic are weakly repelled by a magnet. All substances not possessing one of the other types of magnetism are diamagnetic.

Common Uses of Magnet

Magnetic recording media. Recording media such as VHS tapes has a reel of magnetic tape. The information that makes up the video and sound is encoded on the magnetic coating on the tape.

Credit, Debit, and ATM Cards. All these cards have a magnetic strip on one side.

Television and computer monitors. Tube type TV and computer screens contain an electromagnet to guide electrons to the screen.

Speakers and microphones. Most speakers employ permanent magnets and current carrying coil to convert electric energy to mechanical energy.

Electric motors and generators. Some electric motors work depending on a combination of an electromagnet and a permanent magnet. It converts electrical energy into mechanical energy.

Electric guitars. These guitars use pickups to transduce the vibration of guitar strings into electrical current that can be amplified.

Magnetic compass. A magnetic compass uses a permanent magnet to align itself with a magnetic field, the earth’s magnetic field.

Demagnetizing A Permanent Magnet

For demagnetizing a permanent magnet, a certain required magnetic field must be applied and the threshold to demagnetize depends upon the coercivity of the material. Hard materials have high coercivity value whereas the soft materials have low coercivity.

Magnetized ferromagnetic materials can be demagnetized by

Heating a magnet past its curie temperature, the molecular motion destroys the alignment of the magnetic domains.

Placing the magnet in an alternating magnetic field with intensity above the material’s coercivity and slowly drawing the magnet out and decreasing the magnetic field.

Hammering or jarring, the mechanical disturbance will randomize the magnetic domains.

Characteristics of An Alternating Waveform

An alternating current or voltage is the flow of electric charge with periodical reversal in direction. AC voltage or current has a waveform, which represent the frequency of the source. The magnitude of an AC voltage or current, changes with time. The alternating sine current or voltage waveform is a graphical representation of an alternating current or voltage. It can be plotted on a graph with a vertical and horizontal axis. The amplitude of the waveform such as the current or voltage is indicated on the vertical axis measured in volts and the time is indicated on the horizontal or x-axis and it is measured in either seconds or in degrees. An alternating current cycle consists of 360 degrees. As the AC continually changes direction between positive and negative, it plots a waveform represented by a curved line that shifts constantly from positive to negative and then from negative to positive, crossing zero in between.

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Peak Value of an AC

The peak value of an alternating voltage or alternating current is the highest value reached during a cycle. It is the value or amplitude of an AC voltage, which constantly fluctuates. From an initial zero, the amplitude of the AC rises to a high value or a positive peak, which is called the peak value. It then falls back to zero. After reaching zero, the direction of the current changes and the voltage reaches a negative peak value, or a negative peak. The maximum positive peak value occurs at 90 degrees and the maximum negative peak value occurs at 270 degrees. The peak values are the maximum amplitude levels that a waveform will achieve in its travel.

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Instantaneous Voltage of an AC

An instantaneous voltage is the value of the AC voltage at a particular instant. It is also called as the average voltage. The voltages that can be measured at different points of the cycles of the sine waveform are the instantaneous voltages for that sine wave. It is practically impossible to measure the instantaneous voltages. One of the ways of denoting the instantaneous voltage is by taking the average voltage. The average voltage can be measured by multiplying the peak voltage by a constant, which is around 0.367.

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Root Mean Square Voltage of an AC

RMS voltage may also be called the effective voltage and it is the voltage read by a voltmeter. A given RMS voltage provides the same amount of power as the same value of DC voltage. RMS voltage is the AC voltage in terms of how much DC voltage it would take to have the same effect in a circuit. During most of the cycle the AC has a value less than the value at its peak than a constant DC voltage. So AC voltage will not be able to produce as much heat in a heating element than a constant DC voltage. The power of the AC voltage is proportional to either E squared "E2" or I squared "I2".

P = E2/R

or

P =  I2R

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If all the instantaneous values of a half cycle of a sine wave current or voltage are squared, then the average or mean of all the squared values is found. The square root of this mean value will be 0.707 of the peak value. The RMS value or root mean square value is 70.7 percent of the peak value. The root mean square value represents how effective a sinusoidal AC will be in comparison with its peak value. For determining a peak value of AC that will be effective as a given DC, it is necessary to multiply the effective value given by the reciprocal of 0.707. Reciprocal of 0.707 is

1/0.707 = 1.414

A voltage of 230 volts AC indicates the RMS value and it dissipates the same amount of heat as 230 V DC when applied to the same heater elements. For a domestic supply the effective voltage is 230 volt AC and the peak voltage is 325 V.

The average value of a full cycle of a sine waveform is zero, and it is 0.367 of the maximum voltage or current for a half cycle of the sine wave.

Phase of an AC

Phase denotes the position in angles of the varying voltage from a given instant. When identical amplitude variations of wave forms occur simultaneously they are said to be in phase. When identical amplitude variations do not occur simultaneously they are said to be out of phase.

Alternating Current And Its Applications

Alternating current or alternating voltage is the current or voltage that changes its amplitude in a waveform through a conductor or medium as it flows.  It is the flow of electric current or voltage that reverses its direction in each alternation. Alternating current is abbreviated as AC. The flow of  charge reverses its direction in a circuit back and forth creating an alternating current. The magnitude of an alternating current increases from zero to a maximum for a moment and then returns back to zero.

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AC Waveform

The usual waveform of an AC circuit is a sine wave. In other applications different waveforms are used such as the triangular or square waveforms. The direction of an AC alternates between both directions either positive or negative. The AC voltage changes its waveform from zero to positive and then to zero, zero to negative and then to zero. The rate of alternation of the alternating current is cycles per second. The frequency of an AC voltage or AC current is the number of cycles per second. The frequency of an AC is measured in hertz or Hz in short. The cycles of direction change is usually about 50 to 60 cycles per second, that occurs continuously. The time taken by the AC current or voltage to complete once cycle is known as its time period.

F "Frequency in Hertz" = 1 / T "Time in Seconds"

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Sources of AC

Alternating current is produced by alternators, generators, dynamos, oscillators, signal generators, etc.

Uses of AC

Alternating current is the type of electricity used in domestic and business houses. The cycles of direction change is usually dependent upon the type of electrical system of the place. The AC is used in our houses for lighting and heating purposes. The devices that run on AC are lighting devices, electric fans, coolers, air conditioners, electric iron, electric oven, washing machines etc.

Advantages of AC

1. Alternating current or AC can be changed from one voltage to another of the same frequency. The varying current and voltage induces a varying magnetic field in a transformer, which in terms transforms it into another voltage.

2. AC generators and motors are very simpler in design and manufacture than DC generators and motors.

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AC Applications

AC allows the transmission of electricity  through long distances from where it is generated to where it is  consumed. Very high AC voltage in the range of several 1000s of volts  are used for carrying energy from the power house to the substation. From the substation the high voltage is transformed into lower voltage which is supplied for the domestic purposes.

Signal waveform transformation and transmission is possible only through AC. Signals such as audio, radio etc. are carried by alternating currents of those signal frequencies.

AC transformers are used for converting higher voltage AC to lower volt AC and vice versa. It also couples similar voltage AC from one circuit to another for matching and coupling.

AC motors are used in fans, compressors, starter motors, water pumps, electric vehicles, electricity operated flights, etc. for their respective functions.

Alternating current can pass through inductance and capacitance and produce capacitive reactance and inductive reactance used for signal tuning and transformation.

Direct Current And Its Applications

Direct current is the unidirectional flow of electrons from an area of negative charge to an area of positive charge through a conductor. A direct current always flows in one direction as it flows from one point to another. A DC voltage is always positive or it is always negative. DC voltage has a fixed polarity and the magnitude of the current is constant. It may increase or decrease in intensity but constant in amplitude. The flow of electric current originates from the positive terminal towards the negative terminal. The direction of the electron flow is from the negative terminal of the battery to the positive terminal. The graphical representation of a DC voltage is a straight line across the time-line with a constant voltage level.

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Definition Of DC

A DC refers to a voltage with a single polarity of voltage or current. It also refers to constant, zero frequency, or slowly moving mean value of a voltage or current. The voltage across a DC voltage source is constant as is the current through a DC current source. Direct current in an electric circuit has constant voltage and constant current. A stationary voltage or current has a DC component and a zero time varying component. 

Sources of DC

The sources of direct current are batteries, thermocouples, solar cells, capacitive storage etc. Fuel cells also produce DC by mixing hydrogen and oxygen with a catalyst, producing DC electricity and water as byproduct. Direct current may also be obtained by rectification and filtration of an alternating current or AC from a generator, which is a pulsating DC. The direct current can flow through a conductor such as electrical wires and cables. DC can also flow through semiconductors, insulators, or even through vacuum.

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Most electronic circuits require a direct current that is steady and constant in amplitude for their smooth functioning. Some circuits such as lamps, heaters, and some type of motors may work with a pulsating DC.

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DC Applications
Direct current is used for powering most electronic devices, charge batteries, run motors etc.  It is also commercially used in the production of aluminum and other metals, separation of metals, electroplating, and other electrochemical processes. Telephones are connected to wires that carry DC for their functioning and telephone exchanges have communication equipment that works on direct current. Direct current is used in driving electrical vehicles such as electric cars, bikes, carts, trams, rail etc.  High voltage direct current is used to transmit electricity from the generator site to the place where it is used and to interconnect intermittent power grids.

Working Of a Semiconductor Diode

A semiconductor diode is an electronic component made up joining a block of P-type of semiconductor and an N-type of semiconductor in a single crystalline form. Most of these diodes are made of silicon, although germanium diodes are also available. The semiconductor diodes are also called as a PN junction diode. These diodes are used for a variety of applications such as rectification, voltage regulation, detection, light emission, solar cells, photo detection, etc.

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When a potential is given to the terminals of a diode, the current can flow only in one direction. The current flows through the diode only when the positive of the battery is connected to the P side of the diode and the negative of the battery is connected to the N side of the diode. This is called as the forward bias condition. The diode also has a junction potential of 0.6 volts where  the conduction or flow of current takes place through the  diode. Only when the voltage across the terminals crosses 0.6 volts in  the forward bias mode the conduction of the diode takes place. In the forward bias condition, the positive holes are repelled by the positive anode and the free electrons are repelled by the cathode the negative terminal of the battery. The electrons and holes move across the junction and they combine together. More electrons are siphoned off by the  positive anode and move through the terminals and through the battery. The holes thus created moves across to the N side through the PN junction. Thus a steady current flows through the diode.

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In the reverse bias condition, the positive of the battery is connected to the N side of the diode and the negative  of the battery is connected to the P side of the diode.  Here the diode is at an off or non conducting position. The electrons are attracted to the positive pole of the battery. The holes in the P side of the diode are attracted to the negative of the battery.  The  electrons and holes leave the junction creating an area completely devoid of electrons or holes. This area which is devoid of either electrons or holes is called as a depletion zone. There is no conduction of the diode in the reverse biased diode.

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When an AC voltage is applied to the terminals of the diode, the diode conducts during the alternate halve cycles of the AC waveform and cuts off the voltage during the reverse cycles. The resultant waveform is the broken DC pulses during alternate half cycles of the  AC waveform. A full waveform can be obtained using a transformer and diode combination. The DC pulses can be smoothed out by various waveform filters to obtain a smooth DC voltage.

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When the voltage is increased in a reverse biased diode, the depletion zone becomes wider.  At a critical point, the depletion field becomes large enough so that the carrier, either the electron or hole gain sufficient momentum to break electrons from the atoms with which it collides. These stripped electrons gains sufficient speed until it collides with other atoms striking still more electrons. The operation is accelerated by heat and heated generated carriers in the depletion zone. This process is called as the avalanche. At the avalanche area, the diode begins to conduct in the reverse mode. Usually the breakdown voltage is much higher than the the voltage used in the circuit. There are diodes which operate in the avalanche region and these are called as the zener diodes, which are voltage regulator diodes.

Conduction In a Semiconductor

Semiconductors are substances that are used to make electronic components such as diodes, transistors, solar cells, integrated circuits, microprocessors etc. These semiconductor electronic components are used in the construction of all electronic gadgets and devices ranging from radios, music systems, television, solar panels, telephones, mobile phones, computers, laptops, e notebooks etc. Therefore semiconductors are fundamental in the field of electronics and construction of electronic devices.

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The semiconductors have replaced the valves in most electronic circuitry. Semiconductor devices are light weight and have small physical dimensions, high efficiency and low power losses, ability to overcome vibrations, long life and durability of the components, and requires low voltage and power supplies.

 

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A semiconductor is a substance with an electrical conductivity that lies between a conductor and an insulator.  The semiconducting materials are mostly crystalline in nature and include carbon, silicon, germanium, mixtures of arsenic, selenium, tellurium, etc. The atoms of germanium and silicon  have 4 electrons in their outer orbits.  As there are many atoms in their crystalline structure, electron sharing occurs. This sharing behavior causes their outer electrons become tightly bonded to their respective places in the crystal.  This type of bonding is called  covalent bond.  Although these are covalently bonded in their crystalline structure, these covalent bonds are weak in semiconductors.  The bonds are broken at higher temperatures above absolute zero and more  bonds are broken when the temperature goes higher. When the covalent bonds are broken,  an electron becomes free that can be moved by an electric field.  The place that is left by the free electron becomes a hole. A free place is available in the atom where the electron has left which is the hole. An electron is electrically negative and a hole is electrically positive in charge.

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In the absence of any electrical charge, free electrons are distributed evenly throughout the semiconductor. The electrical charge in semiconductor exists as electron-hole pairs. The electrons are being captured by the holes resulting in the destruction of the  electron-hole pairs. When a hole captures an electron, the hole no longer exists and the electron is no longer a free electron.  Electron and hole pairs are being constantly created and destroyed in about equal numbers.

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When an electrical charge is applied across a block of semiconductor, electrons are attracted to the positive end of the semiconductor block. Electron hole pairs are formed rapidly throughout the block due to the electric charge. There is heavy concentration of electrons at the positive end and only fewer electrons are left at the negative end of the block. More electrons move towards the positive end by the steady application of electrical charge. The holes at the negative end of the block cannot capture electrons because there are almost none for them to capture. At the positive end of the semiconductor block there is an excess of electrons and at the negative end there is an excess of holes. More electron hole pairs are formed at the positive end as long as the temperature breaks the electrons loose from their bonds. Thus the conduction on a pure semiconductor is dependent on the temperature and the charge given.

Capacitance And Its Measurement

A capacitor is a device, which is used to store an electrical charge or electrical energy. Capacitor consists of 2 electrical conductors separated by a dielectric medium. Capacitance is the measure of the capacitor to store electrical charge. It is the property of an electric circuit which tends to oppose a change in voltage when a potential difference is applied. Capacitance exists when two electrical conductors are separated by a nonconducting medium or a dielectric material.

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Charging Of a Capacitor

When a battery is connected across 2 metal plates, the positive terminal attracts the negative  electrons in plate 1 of the plates. The excess of electrons on the negative of the battery rush to the plate 2 of the capacitor and gets accumulated. More and more electrons leave the plate 1 to the positive terminal of the battery and and more electrons crowd to the plate 2 from the negative terminal. A positive charge accumulates in the plate 1 and a negative charge gets accumulated in the plate 2.  The charges on the two plates increase in opposite directions until the difference between them is exactly equal to the difference in potential between the two terminals of the battery. At this point, the electrons stop flowing as there is a balance in forces of the charged plates. When a dielectric material such as glass or plastic is placed in between the plates, the capacitance increases as seen by the deflection of an ammeter connected in the circuit.

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The unit of capacitance is farad. A capacitor has a capacitance of 1 farad when 1 volt difference in voltage results in the storage of 1 coulomb of charge. Usually capacitors are denoted in micro farads, nanofarads, picofarads, etc. An ideal capacitor is characterized by a constant capacitance C, defined as a ratio of charge + or - Q on each conductor to the voltage V between them.

C = Q/V

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The charge build up in the capacitor affects the capacitor mechanically that varies its capacitance, where the capacitance is measured in incremental changes.

C = dq/dv 

Calculating current flow through the capacitor

Formula of current, I = dQ/dt

The formula for current with respect to time is dQ/dt = d(CV)/dt

it is expressed as I = C (dV/dt)

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Capacitors are used in electronic circuits for blocking DC voltage, allowing passage of AC, resonant circuits in radio, filter circuits, power supply smoothing, timing circuits, switching circuits, stabilizing power and voltage flow etc.

A capacitor has undesirable characteristics and limitations such as leakage current when the dielectric between the conductor plates of the capacitor passes a small leakage current through it. Capacitor has an electric field strength limit, resulting in a breakdown voltage for each. Also the leads and plates of the capacitor introduces some unnecessary inductance and resistance to the circuit.

Factors That Determine the Capacitance

The capacitance of a capacitor differs based on

1. The area of the plate surface that are directly opposite to each other. Increasing the plate area will increase the capacitance.

2. Distances between the plates. The smaller the distance between the plates, the bigger is the capacitance.

3. Type of dielectric. The type of dielectric that the capacitor is using does have an influence on the capacitance. Some dielectrics offers more capacitance than that using other types of dielectric.

The greater the surface area of the plates, the higher is the capacitance. The closer the distance between the plates, the higher is the capacitance. The greater is the dielectric constant of the dielectric, the higher is the capacitance.

Capacitance in Series and Parallel

Capacitors can be connected in series and parallel combination for various reasons. The need for connecting capacitance in combination are to increase or decrease the capacitance, reduce fluctuations due to heat, improved filtering, achieve higher voltage rating, obtaining high Q etc. Capacitors are combined in series to achieve higher voltage as in smoothing a higher voltage AC, the voltage rating of each capacitor adds up. Series combination is also used to connect polarized capacitors  connected back to back to form a bipolar capacitor.

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Capacitors Connected in Series

When capacitors are connected in series, the total capacitance can be reduced. The separation distance of the capacitor increases and not the plate area. Each capacitor stores the charge that is equal to that of every other capacitor in series. The voltage difference at the terminals of each capacitor is distributed among the capacitors according to the inverse of their capacitance. The effective capacitance is smaller than the smallest of any one of the capacitor connected to it.

The capacitors of capacitance C1, C2, C3,  - - - Cn are connected in series and the total capacitance is measured by the formula.

1/C = 1/C1 + 1/C2 + 1/C3 + - - - 1/Cn

For example, the three capacitors with capacitance 10 microfards, 5 microfarads, 5 microfarads are connected in series, it is written as

1/C = 1/10 + 1/5 + 1/5

1/C =  1+2+2/10

C = 2 microfarads

Capacitors Connected in Parallel

When capacitors are connected in parallel, the total capacitance is the sum of all the capacitors. All the capacitance adds up and the effective capacitance increases. Each capacitor have the same applied voltage across its terminals. There is equal distribution of charge through all capacitors depending on the size. Each capacitor contributes to the total surface area of the capacitor.

The capacitors of capacitance C1, C2, - - - C3 are connected in parallel and the total capacitance is measured by the formula.

C = C1 + C2 + C3 - - - + Cn

For example, the three capacitors with capacitance 10 microfards, 5 microfarads, 15 microfarads are connected in parallel, it is written as

C = 10 + 5 + 15

C =  30 microfarads

Capacitor Color Codes

The capacitors have specific values which are marked on to the body of the capacitor, that helps to understand the capacitance and other properties of it. The important values for the capacitor are the capacitance, tolerance, voltage rating, temperature coefficient etc. These are usually marked on the body of the capacitor in the alphanumeric form. There are many decimal values that are used as capacitor values where the reading becomes difficult without the help of a capacitor value chart. To reduce the confusion involved with the letters, numbers, and decimals used in representing capacitor values and also to prevent misreading the values of the capacitor, an international color coding scheme was introduced.  The capacitor color code represents a simple and efficient way of reading capacitor values and tolerances.

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There are different build of non polarized capacitors such as the axial lead, radial lead, and ceramic disc capacitors. The disc type of capacitor color code is read from the top of the capacitor to the bottom of the capacitor. The extreme end of the body of the capacitor is considered as top of the capacitor and towards the axial leads is considered as the bottom of the capacitor. The color marking at the top of the capacitor is considered as the first color band. In radial and axial lead type of capacitors the ring near any of the lead is considered as the first color band.

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The first band A is usually the value for the temperature coefficient of the capacitor, which is denoted as A. The second band B is the first digit of the capacitor in picofarads, denoted as B. The third band C is the second digit of the capacitor in picofarads, denoted as C. The fourth band D is the multiplier of the capacitance in multiples of 10, denoted as D.  The fifth band E is the tolerance of the capacitor in percentage, denoted as E.

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More recently a different type of capacitor coding has come to be in use. In small types of capacitors such as film or disc form, instead of the color coding, the capacitance is given as a letter or a number code. The code consists of 2 or 3 numbers and an optional tolerance letter code to identify the tolerance.

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When a 2 letter code is used, the value of the capacitor is denoted in picofarads such as 10 = 10pf, 22 = 22 pf, and 100 = 100 pf etc. The 3 letter code is used to denote the value of capacitor, the first two digits for the first and the second value of the capacitor and the third one is multiplier in picofarads which multiplies in multiples of 10. For example a capacitor with a value 251 = 25 * 10 = 250 pf and 102 = 10 * 100 = 1000 pF etc. There is an additional letter included in a 3 digit code to include the tolerance measurement of the capacitor. For example a capacitor with a value 103J printed on the body, which denotes the 1st and 2nd digits as the 1st and 2nd value of the capacitor and the 3rd one is denoted as the multiplier in picofarads and the letter J is the tolerance.

10 * 1000 = 10,000 pf and the letter J denotes a tolerance of +/- 5%

The capacitance is 10,000 pF which is equivalent to 10 nF or 0.010 mF with a tolerance of +/- 5%

Resistor Color Codes

An electronic color code is used in most electronic components including the resistors. Most of the axial lead resistors are marked with the color rings, which gives the value of the resistor. The rings are printed on the body of the resistor and there will be 3 to 6 rings in total. The resistor color code gives the exact value of the resistor and its tolerance. The nearest ring to the end is taken as the first ring. The resistor value rings for the 1st digit, 2nd digit, and 3rd digit will be adjacent to each other. The resistor is held with the first ring to the left and then the color code is read from the left to the right. Reading the resistor is easier with the 5% and 10% tolerance resistor as it is at the opposite end of the first resistor ring, which is marked as silver or gold.

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For a 4-band resistor, the first ring indicates the first figure of the value in ohms. The second ring indicates the second figure of the value in ohms. The third ring indicates the multiplier which is the number of zeroes that will come on the right side of the value. The fourth ring indicates the tolerance of the resistance, which is expressed in percentage. If there is only 3 rings and no fourth ring, it indicates that the tolerance is 20% for that resistor.

For a 6-band resistor, the first ring indicates the first figure of  the value in ohms. The second ring indicates the second figure of the value in ohms. The third ring indicates third significant digit of the value in ohms. The fourth ring will be taken as the multiplier. The fifth ring indicates the tolerance of the resistance. The sixth ring indicates the temperature coefficient of the resistor.

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Resistance Value of The Resistor

The first 2 bands indicate the value of the resistor in a 4 band resistor. The first 3 bands indicate the value of the resistor in a 6 band resistor.

Black – 0

Brown – 1

Red – 2

Orange – 3

Yellow – 4

Green – 5

Blue – 6

Violet – 7

Grey – 8

White – 9

Multiplier Value of The Resistor

The third band indicates the multiplier value in a 4 band resistor. The fourth band indicate the multiplier value in a 6 band resistor.

Black – x1

Brown – x10

Red – x100

Orange – x1K

Yellow – x10K

Green – x100K

Blue – x1M

Violet – x10M

Grey – x100M

White – x1G

Gold – .1

Silver – .01

Tolerance of The Resistor

The fourth band indicates the tolerance of the resistor in a 4 band resistor. The fifth band indicate the tolerance of the resistor in a 6 band resistor.

Brown – 1%

Red – 2%

Orange – 3%

Yellow – 4%

Green – .5%

Blue – .25%

Violet – .1%

Gray – .05%

Gold – 5%

Silver – 10%

No color - 20%

Temperature Coefficient of The Resistor

Resistor values change with the change in temperature. The sixth band in a 6-band resistor is a temperature coefficient or tempco of the resistor, which represents the amount of resistance value that will change with temperature. It is measured in ppm/degree C. The sixth band represents the following.

Brown – 100 ppm/degreeC

Red – 50 ppm/degreeC

Orange – 15 ppm/degreeC

Yellow – 25 ppm/degreeC

Blue – 10 ppm/degreeC

Violet – 5 ppm/degreeC

An Inductor And Different Types

Inductance   is a   property  in an electronic circuit where a change in current in  a   circuit   creates a voltage in the  circuit itself and also the  nearby   circuits.  A  steady stream of  current in a conductor creates  a   magnetic field  around  the conductor. A  varying magnetic field  in  a   circuit  induces a  voltage in an adjacent conductor. An inductor is    a  passive electrical  component that stores energy in its magnetic     field.  Inductance is  created from the magnetic field that is formed    around a  conductor which  carries current that tends to oppose the change in current.

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Inductor Property

All conductors have inductance and can be made  into an inductor. A   length   of conductor can become an inductor and the  inductance will   be  greater  when it is wound into a coil. An inductor is  usually a    conductor turned  into a coil form, which concentrates or  increases   the  magnetic field  of the conductor.   An  electric current   through a inductor creates a magnetic flux or    magnetic field. A change  in the electric current also creates a    change  in the magnetic flux  which is proportional to the current.

Self Inductance

A     conductor has self inductance where a  change in the electric   current    through a circuit having inductance induces a proportional    voltage  that  opposes the change in  current. A varying magnetic field   in the  coil is  needed for inducing an opposing voltage  in the coil.   The  changing magnetic flux  generates an electromotive  force that   opposes  the change in current. This changing magnetic flux  induces a   voltage in  the coil. This voltage tend to oppose the change  and will    try to  decrease the current if it is increasing or increase  the   current  if it  is decreasing. This opposing flow of electric current is termed  as  self induction. Self inductance can be illustrated using an experiment. Here a battery is connected through a switch across a coil wound many times on an iron     core. A small lamp that lights on battery voltage is connected  across    the terminals of the  coil. An ammeter is connected in series to     the coil and the switch. When the switch is opened, the ammeter    reading  falls to zero but the lamp flashes very brightly and goes out.

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Mutual Inductance

Mutual     inductance happen when the coils are kept near so that the magnetic     flux from one inductor cross to the other and thus they exhibit  mutual    inductance. It is the phenomenon of production of induced  current in   one  coil by changing the magnetic flux due to current in  another coil.    The varying current in  the coil or circuit induces a voltage in an    adjacent coil or circuit  is called as mutual inductance. Mutual    inductance between coils  depends upon their coefficient of coupling,    which can vary from 0 to  1.

Factors Affecting Inductance

The inductance of an inductor depends on

1. The number of loops of the coil. The larger the number of turns the greater is the inductance.

2. The size of each loop. The greater the size of the loop, the greater is the inductance.

3. The permeability of the material used as the former to wind the  coil. The magnetic flux can be increased by coiling the conductor  around a    material with high permeability. Materials with high  permeability    includes soft iron, ferrite, etc.

4. Cross section of the core. The larger the cross section of the core, the higher the inductance.

5. Spacing of the turns. The smaller the spacing between the turns of the coil the greater is the inductance.

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The unit of measurement of inductance is the henry and the symbol for inductance is L 

An inductor of 1 henry of inductance produces an EMF of 1 volt when the current through the inductor changes at the rate of 1 ampere per second. Henry is a large unit and smaller units are usually used in    practice  especially in radio, where millihendry mH or microhenry microH are used.

The relationship between self inductance L, voltage, and current in a circuit is

V = L * di/dt

Where     V is the voltage in volts, L is the self inductance, i is the  current    in amperes,  and t is the time.  The voltage across the  inductor is    proportional to the product of its inductance and the  time rate of    change of the current through it.

Inductance     is present in almost all circuits which may have beneficial or     detrimental effects to the function of the circuit.  Inductors can be     used where the current and voltage changes with time. Inductors have    the  ability to  delay and shape alternating currents. Common   inductors   consists of a specific number of turns of enamelled copper wire, wound around  a  former such as air, iron, laminated steel, ferrite, Teflon etc.

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An   ideal inductance has inductance but no resistance or capacitance and   does not dissipate or radiate energy. However real inductance have     resistances due to the resistance of the wire and the parasitic     capacitances due to electric field between the turns of the coil    having slightly different potentials. Energy is dissipated by the    resistance of the wire and by the losses of the magnetic core due to    hysteresis. 

Uses and Effects of Inductance

Inductances   are widely used in radio circuits, other analog circuits, and signal   processing. Inductances provide frequency selection in a tuned circuit   of the radio. Large inductors are used in power supplies to filter out   mains hum, power supply noises, and   fluctuations in the DC. Inductors are used in  filter  circuits  to   filter out waveforms or in energy storage systems. Audio  chokes have   many turns of wire on iron core, which has inductances of 1  to 100  henrys.   Radio frequency chokes  have inductances of a few turns of  wire wound  on  a nonmagnetic core. Power transformers are used in power  supplies  for most electronic equipments. Coupled magnetic fluxes  between a  stationary and a rotating inductor coil is used to   produce mechanical torque in induction motors. Inductors are used as  an  energy storage device in switch-mode power supplies. Variable  inductors  use an adjustable core, which is  usually a ferrite  core or  powdered  iron core, that can change the  inductance.

Inductances    are found in transmission cables that   determine the characteristic    impedance in a cable. Inductances are  also  seen in microphone and    computer network cables that use special  cables  to reduce it. Long    power transmission lines also shows  inductances which  limits the AC    power that can be sent through them.

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Types of Inductances

There are 2 types of inductors, fixed inductor and the variable inductor.

Fixed   inductors are air core inductor, radio frequency inductor,   ferromagnetic core inductor, laminated core inductor, ferrite-core   inductor, and toroidal core inductor.

Variable   inductors are  widely used in radio applications to set a definite   oscillating frequency and to tune the resonant circuits. These may   include many different types of slug tuned inductors. Slug tuned   inductors are widely used in RF and IF stages of super heterodyne radio receivers. Tuned inductors are also used as the tank coil in the final RF power amplifiers.