The Electric Circuit Leo2

The Electric Circuit An electric circuit is a collection of physical components. These components combine to utilize voltage(V), current (I), and resistance (R). The circcuit consists of components which can provide V, R, and I. A battery or power supply usually provides the voltage. Conductors consist of copper wires and in many of today's application fiber cable. Loads come in all shapes and sizes and vary from simple resistance to very complex circuits. Figure 3-1 shows a pictorial for a simple electric circuit. Components of a circuit include the following items. Voltage source Loads Switches Fuses/Circuit breakers Conductors – Wires Grounds

Figure 3-1 Pictorials show an excellent layout of an electric circuit. However, engineers and technicians often prefer to work with a schematic of the circuit. Various symbols are used to designate various circuit components. The pictorial of the simple circuit is redrawn below in schematic form.

Switches

Figure 3.3 Push buttons are used in electric circuits to momentarily open or close a circuit. NOPB is a normally open push button and NCPB is a normally closed push button. The rotary switch is a multiple connection device allowing a single control to make contact between one pole and several contacts. Devices called switches are another type of element used to control the operation of the circuit. Several of the schematic symbols for switches are shown below. The number of contacts called throws and the number of movable arms called poles designates switches. A SPST switch is a single pole single throw switch. This is similar to the light switch found in many buildings. Protection Devices

Figure 3.4 Fuses and circuits breakers are rated for both amperage and voltages. The fuse above is rated at 5 amps in a 220-volt circuit. Fuses and circuit breakers are placed in circuits as protection devices for components to prevent too much current. Wires

Figure 3.5 The cross-sectional area can be determined by the relationship below. A = d2 A -- CM , d -- mils The conductors found in most circuits consist of copper wire. The wires are characterized according to their size. This arrangement is called the American Wire Gage or AWG for short. The size of the wire is determined by the cross-sectional area of the wire and is measured in circular mils (CM). 1CM = 0.001in.

Wire resistance

In any conductor, some resistance to the flow of electrons exists. This resistance is a factor of several characteristics.

Type of material or resistivity --ρ Length of conductor -- l Cross-sectional area -- A Temperature R = ρ l/A Ground

Figure 3.6 When making measurements ground is simply a reference point. Ground is assigned a reference value of 0 volts. All measurements are taken in reference to this point of the circuit. The term ground comes from electrical power distribution. One side of the power line is connected directly to earth’s ground by copper rods. In an electric circuit, the chassis of the equipment serves as one type of ground called chassis ground. Another often used reference point is the circuit itself thus the name reference ground. Ground provides a path for current to return to the battery or power source. The schematic symbols for the grounds are shown below.

Figure 3.7 Basic Circuit Measurements Instruments Voltmeter Measures voltage V Ammeter Measures currentI Ohmmeter Measures resistance R Multimeter Combination of all the above instruments

Types

Electronic component An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads. Components are intended to be connected together, usually by soldering to a printed circuit board, to create an electronic circuit with a particular function (for example an amplifier, radio receiver, or oscillator). Components may be packaged singly (resistor, capacitor, transistor, diode etc) or in more or less complex groups as integrated circuits (operational amplifier, resistor array, logic gate etc). Very often electronic components are mechanically stabilized, improved in insulation properties and protected from environmental influence by being enclosed in synthetic resin Components may be Passive or Active: • •

Passive components are those that do not have gain or directionality. [1]. In the Electric industry they are called Electrical elements or electrical components Active components are those that have gain or directionality, in contrast to passive components, which have neither. They include Semiconductors (Solid State Devices) and Thermionic Valves (Vacuum Tubes)

Wire A wire is a single, usually cylindrical, elongated strand of drawn metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Standard sizes are determined by various wire gauges. The term wire is also used more loosely to refer to a bundle of such strands, as in 'multistranded wire', which is more correctly termed a cable. Wire has many uses. It forms the raw material of many important manufacturers, such as the wire-net industry, wire-cloth making and wire-rope spinning, in which it occupies a place analogous to a textile fiber. Wire-cloth of all degrees of strength and fineness of mesh is used for sifting and screening machinery, for draining paper pulp, for window screens, and for many other purposes. Vast quantities of aluminum, copper, nickel and steel wire are employed for telephone and data wires and cables, and as conductors in electric power transmission, and heating. It is in no less demand for fencing, and much is consumed in the construction of suspension bridges, and cages, etc. In the manufacture of stringed musical instruments and scientific instruments wire is again largely used. Among its other sources of consumption it is sufficient to mention pin and hair-pin making, the needle and fish-hook industries, nail, peg and rivet making, and carding machinery; indeed there are few industries into which it does not enter. Not all metals and metallic alloys possess the physical properties necessary to make useful wire. The metals must in the first place be ductile and strong in tension, the quality on which the utility of wire principally depends. The metals suitable for wire, possessing almost equal ductility, are platinum, silver, iron, copper, aluminum and gold; and it is only from these and certain of their alloys with other metals, principally brass and bronze, that wire is prepared. By careful treatment extremely thin wire can be produced. Special purpose wire is however made from other metals (e.g. tungsten wire for light bulb and vacuum tube filaments, because of its high melting temperature).

History In antiquity, jewelery often contains, in the form of chains and applied decoration, large amounts of wire that is accurately made and which must have been produced by some efficient, if not technically advanced, means. In some cases, strips cut from metal sheet were made by pulling them through perforations in stone beads. This causes the strips to fold round on themselves to form thin tubes. This strip drawing technique was in use in Egypt by the 2nd Dynasty. From the middle of the 2nd millennium BC most of the gold wires in jewelery are characterized by seam lines that follow a spiral path along the wire. Such twisted strips can be converted into solid round wires by rolling them between flat surfaces or the strip wire drawing method. Strip and block twist wire manufacturing methods were still in use in Europe in the 7th century AD, but by this time there seems to be some evidence of wires produced by true drawing. Square and hexagonal wires were possibly made using a swaging technique. In this method a metal rod was struck between grooved metal blocks, or between a grooved punch and a grooved metal anvil. Swaging is of great antiquity, possibly dating to the beginning of the 2nd millennium BC in Egypt and in the Bronze and Iron Ages in Europe for torches and fibulae. Twisted square section wires are a very common filigree decoration in early Etruscan jewelery. In about the middle of the 2nd millennium BC a new category of decorative wires was introduced which imitated a line of granules. Perhaps the earliest such wire is the notched wire which first occurs from the late 3rd, early 2nd millennium BC in Anatolia and occasionally later. Wire was drawn in England from the medieval period. The wire was used to make wool cards and pins, manufactured goods whose import was prohibited by Edward IV in 1463.[1] The first wire mill in Great Britain was established at Tintern in about 1568 by the founders of the Company of Mineral and Battery Works, who had a monopoly on this.[2] Apart from

their second wire mill at nearby Whitebrook,[3] there were no other wire mills before the second half of the 17th century. Despite the existence of mills, the drawing of wire down to fine sizes continued to be done manually. Wire is usually drawn of cylindrical form; but it may be made of any desired section by varying the outline of the holes in the draw-plate through which it is passed in the process of manufacture. The draw-plate or die is a piece of hard cast-iron or hard steel, or for fine work it may be a diamond or ruby. The object of utilizing precious stones is to enable the dies to be used for a considerable period without losing their size, and so producing wire of incorrect diameter. Diamond dies must be rebored when they have lost their original diameter of hole, but the metal dies are brought down to size again by hammering up the hole and then drifting it out to correct diameter with a punch.

Production Main article: wire drawing Wire is often reduced to the desired diameter and properties by repeated drawing through progressively smaller dies, or traditionally holes in draw plates. The wire may be heated to red heat in an inert atmosphere to soften it, and then cooled, in a process called annealing. An inert atmosphere is used to prevent oxidation, although some scaling always occurs and must be removed by 'pickling' before the wire is redrawn. An important point in wire-drawing is that of lubrication to facilitate the operation and to lessen the wear on the dies. Various lubricants, such as oil, are employed. Another method is to immerse the wire in a copper (II) sulfate solution, so that a film of copper is deposited which forms a kind of lubricant, easing the drawing considerably. In some classes of wire the copper is left after the final drawing to serve as a preventive of rust or to allow easy soldering. The wire-drawing machines include means for holding the dies accurately in position and for drawing the wire steadily through the holes. The usual design consists of a cast-iron bench or table having a bracket standing up to hold the die, and a vertical drum which rotates and by coiling the wire around its surface pulls it through the die, the coil of wire being stored upon another drum or "swift" which lies behind the die and reels off the wire as fast as required. The wire drum or "block" is provided with means for rapidly coupling or uncoupling it to its vertical shaft, so that the motion of the wire may be stopped or started instantly. The block is also tapered, so that the coil of wire may be easily slipped off upwards when finished. Before the wire can be attached to the block, a sufficient length of it must be pulled through the die; this is effected by a pair of gripping pincers on the end of a chain which is wound around a revolving drum, so drawing the pincers along, and with them the wire, until enough is through the die to be coiled two or three times on the block, where the end is secured by a small screw clamp or vice ready for the drawing operation. Wire has to be pointed or made smaller in diameter at the end before it can be passed through the die; the pointing is done by hammering, filing, rolling or swaging in dies, which effect a reduction in diameter. When the wire is on the block the latter is set in motion and the wire is drawn steadily through the die; it is very important that the block shall rotate evenly and that it shall run true and pull the wire in an even manner, otherwise the "snatching" which occurs will break the wire, or at least weaken it in spots. Continuous wire-drawing machines differ from the single-block machines in having a series of dies through which the wire passes in a continuous manner. The difficulty of feeding between each die is solved by introducing a block between each, so that as the wire issues it coils around the block and is so helped on to the next die. The speeds of the blocks are increased successively, so that the elongation due to drawing is taken up and slip compensated for. The operation of threading the wire first through all the dies and around the blocks is termed "stringing-up." The arrangements for lubrication include a pump which floods the dies, and in many cases also the bottom portions of the blocks run in lubricant. The speeds at which the wire travels vary greatly, according to the material and the amount of reduction effect

Solid wire and stranded wire Solid Solid wire or solid-core wire consists of one piece of metal wire. Solid single strand wire is is cheaper to manufacture than stranded wire and is used where there is no need for flexibility in the wire. Solid wire also provides strength and protection against the environment.

Stranded

Stranded copper wire Stranded wire is composed of a bundle of small-gauge wires to make a larger conductor, which may optionally be insulated. Stranded wire is more flexible than a solid strand of the same total gauge. Stranded conductors are commonly used for electrical applications carrying small signals, such as computer mouse cables, and for power cables between a movable appliance and its power source; for example, sweepers, table lamps, powered hand tools, welding electrode cables, mining machines and trailing machine cables. At high frequencies, current travels near the surface of the wire because of the skin effect, resulting in increased power loss in the wire. Stranded wire might seem to reduce this effect, since the total surface area of the strands is greater than the surface area of the equivalent solid wire, but in fact a simple stranded wire will in fact have worse skin effect than a solid wire, because of its increased average resistivity, due to inclusion of air gaps within the wire. However, for many high-frequency applications, proximity effect (electromagetism) is more severe than skin effect, and in some limited cases, simple stranded wire can reduce proximity effect. For better performance at high frequencies, litz wire, which has the individual strands insulated and twisted in special patterns, can be used.

Switch A switch is a device for changing the course (or flow) of a circuit. The prototypical model is a mechanical device (for example a railroad switch) which can be disconnected from one course and connected to another. The term "switch" typically refers to electrical power or electronic telecommunication circuits. In applications where multiple switching options are required (e.g., a telephone service), mechanical switches have long been replaced by electronic variants which can be intelligently controlled and automated. The switch is referred to as a "gate" when abstracted to mathematical form. In the philosophy of logic, operational arguments are represented as logic gates. The use of electronic gates to function as a system of logical gates is the fundamental basis for the computer—i.e. a computer is a system of electronic switches which function as logical gates.

A simple electrical switch A simple semiconductor switch is a transistor.

Contacts In the simplest case, a switch has two pieces of metal called contacts that touch to make a circuit, and separate to break the circuit. The contact material is chosen for its resistance to corrosion, because most metals form insulating oxides that would prevent the switch from working. Contact materials are also chosen on the basis of electrical conductivity, hardness (resistance to abrasive wear), mechanical strength, low cost and low toxicity[1]. Sometimes the contacts are plated with noble metals. They may be designed to wipe against each other to clean off any contamination. Nonmetallic conductors, such as conductive plastic, are sometimes used.

Actuator The moving part that applies the operating force to the contacts is called the actuator, and may be a toggle or dolly, a rocker, a push-button or any type of mechanical linkage

Contact arrangements A pair of contacts is said to be 'closed' when there is no space between them, allowing electricity to flow from one to the other. When the contacts are separated by a space, they are said to be 'open', and no electricity can flow. Switches can be classified according to the arrangement of their contacts. Some contacts are normally open until closed by operation of the switch, while others are normally closed and opened by the switch action. A switch with both types of contact is called a changeover switch. The simplest form of switch is the knife switch. The terms pole and throw are used to describe switch contacts. A pole is a set of contacts that belong to a single circuit. A throw is one of two or more positions that the switch can adopt. These terms give rise to abbreviations for the types of switch which are used in the electronics industry. In mains wiring names generally involving the word way are used; however, these terms differ between British and American English and the terms two way and three way are used in both with different meanings

Make-before-break, break-before-make In a multi-throw switch, there are two possible transient behaviors as you move from one position to another. In some switch designs, the new contact is made before the old contact is broken. This is known as make-before-break, and ensures that the moving contact never sees an open circuit (also referred to as a shorting switch). The alternative is break-before-make, where the old contact is broken before the new one is made. This ensures that the two fixed contacts are never shorted to each other. Both types of design are in common use, for different applications.

Biased switches A biased switch is one containing a spring that returns the actuator to a certain position. The "on-off" notation can be modified by placing parentheses around all positions other than the resting position. For example, an (on)-off-(on) switch can be switched on by moving the actuator in either direction away from the centre, but returns to the central off position when the actuator is released. The momentary push-button switch is a type of biased switch. The most common type is a push-to-make switch, which makes contact when the button is pressed and breaks when the button is released. A push-to-break switch, on the other hand, breaks contact when the button is pressed and makes contact when it is released. An example of a push-to-break switch is a button used to release a door held open by an electromagnet. Changeover push button switches do exist but are even less common.

Special types Switches can be designed to respond to any type of mechanical stimulus: for example, vibration (the trembler switch), tilt, air pressure, fluid level (the float switch), the turning of a key (key switch), linear or rotary movement (the limit switch or microswitch), or presence of a magnetic field (the reed switch). The mercury switch consists of a drop of mercury inside a glass bulb. The two contacts pass through the glass, and are mechanically joined when the bulb is tilted to make the mercury roll on to them. The advantage of this type of switch is that the liquid metal flows around particles of dirt and debris that might otherwise prevent the contacts of a conventional switch from closing.

Circuit breaker A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.

Operation Magnetic circuit breakers are implemented using a solenoid (electromagnet) whose pulling force increases with the current. The circuit breaker's contacts are held closed by a latch and, as the current in the solenoid increases beyond the rating of the circuit breaker, the solenoid's pull releases the latch which then allows the contacts to open by spring action. Some types of magnetic breakers incorporate a hydraulic time delay feature wherein the solenoid core is located in a tube containing a viscous fluid. The core is restrained by a spring until the current exceeds the breaker rating. During an overload, the solenoid pulls the core through the fluid to close the magnetic circuit, which then provides sufficient force to release the latch. The delay permits brief current surges beyond normal running current for motor starting, energizing equipment, etc. Short circuit currents provide sufficient solenoid force to release the latch regardless of core position thus bypassing the delay feature. Ambient temperature affects the time delay but does not affect the current rating of a magnetic breaker. Thermal breakers use a bimetallic strip, which heats and bends with increased current, and is similarly arranged to release the latch. This type is commonly used with motor control circuits. Thermal breakers often have a compensation element to reduce the effect of ambient temperature on the device rating. Thermomagnetic circuit breakers, which are the type found in most distribution boards, incorporate both techniques with the electromagnet responding instantaneously to large surges in current (short circuits) and the bimetallic strip responding to less extreme but longer-term overcurrent conditions. Circuit breakers for larger currents are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism. Under short-circuit conditions, a current many times greater than normal can flow (see maximum prospective short circuit current). When electrical contacts open to interrupt a large current, there is a tendency for an arc to form between the opened contacts, which would allow the flow of current to continue. Therefore, circuit breakers must incorporate various features to divide and extinguish the arc. In air-insulated and miniature breakers an arc chute structure consisting (often) of metal plates or ceramic ridges cools the arc, and blowout coils deflect the arc into the arc chute. Larger circuit breakers such as those used in

electrical power distribution may use vacuum, an inert gas such as sulfur hexafluoride or have contacts immersed in oil to suppress the arc. The maximum short-circuit current that a breaker can interrupt is determined by testing. Application of a breaker in a circuit with a prospective short-circuit current higher than the breaker's interrupting capacity rating may result in failure of the breaker to safely interrupt a fault. In a worst-case scenario the breaker may successfully interrupt the fault, only to explode when reset, injuring the technician. Small circuit breakers are either installed directly in equipment, or are arranged in a breaker panel. Power circuit breakers are built into switchgear cabinets. High-voltage breakers may be free-standing outdoor equipment or a component of a gas-insulated switchgear line-

Types of circuit breaker There are many different technologies used in circuit breakers and they do not always fall into distinct categories. Types that are common in domestic, commercial and light industrial applications at low voltage (less than 1000 V) include: •

•

MCB (Miniature Circuit Breaker)—rated current not more than 100 A. Trip characteristics normally not adjustable. Thermal or thermal-magnetic operation. Breakers illustrated above are in this category. MCCB (Moulded Case Circuit Breaker)—rated current up to 1000 A. Thermal or thermal-magnetic operation. Trip current may be adjustable.

Electric power systems require the breaking of higher currents at higher voltages. Examples of high-voltage AC circuit breakers are: •

•

Vacuum circuit breaker—With rated current up to 3000 A, these breakers interrupt the current by creating and extinguishing the arc in a vacuum container. These can only be practically applied for voltages up to about 35,000 V, which corresponds roughly to the medium-voltage range of power systems. Vacuum circuit breakers tend to have longer life expectancies between overhaul than do air circuit breakers. Air circuit breaker—Rated current up to 10,000 A. Trip characteristics are often fully adjustable including configurable trip thresholds and delays. Usually electronically controlled, though some models are microprocessor controlled via an integral electronic trip unit. Often used for main power distribution in large industrial plant, where the breakers are arranged in draw-out enclosures for ease of maintenance.

High-voltage circuit breakers Electrical power transmission networks are protected and controlled by high-voltage breakers. The definition of "high voltage" varies but in power transmission work is usually thought to be 72,500 V or higher, according to a recent definition by the International Electrotechnical Commission (IEC). High-voltage breakers are nearly always solenoidoperated, with current sensing protective relays operated through current transformers. In substations the protection relay scheme can be complex, protecting equipment and busses from various types of overload or ground/earth fault. High-voltage breakers are broadly classified by the medium used to extinguish the arc. • • • •

Oil-filled (dead tank and live tank) Oil-filled, minimum oil volume Air blast Sulfur hexafluoride

High voltage breakers are routinely available up to 765 kV AC. Live tank circuit breakers are where the enclosure that contains the breaking mechanism is at line potential, that is, "Live". Dead tank

Brief history The first patents on the use of SF6 as an interrupting medium was filed in Germany in 1938 by Vitaly Grosse (AEG) and independently later in the USA in July 1951 by H.J. Lingal, T.E. Browne and A.P. Storm (Westinghouse). The first industrial application of SF6 for current interruption dates back to 1953. High-voltage 15 kV to 161 kV load switches were developed with a breaking capacity of 600 A. The first high-voltage SF6 circuit-breaker built in 1956 by Westinghouse, could interrupt 5 kA under 115 kV, but it had 6 interrupting chambers in series per pole. In 1957, the puffer-type technique was introduced for SF6 circuit breakers where the relative movement of a piston and a cylinder linked to the moving part is used to generate the pressure rise necessary to blast the arc via a nozzle made of insulating material (figure 1). In this technique, the pressure rise is obtained mainly by gas compression. The first highvoltage SF6 circuit-breaker with a high short-circuit current capability was produced by Westinghouse in 1959. This dead tank circuit-breaker could interrupt 41.8 kA under 138 kV (10,000 MV·A) and 37.6 kA under 230 kV (15,000 MV·A). This performance were already significant, but the three chambers per pole and the high pressure source needed for the blast (1.35 MPa) was a constraint that had to be avoided in subsequent developments. The excellent properties of SF6 lead to the fast extension of this technique in the 1970s and to its use for the development of circuit breakers with high interrupting capability, up to 800 kV.

Resistor A resistor is a two-terminal electrical or electronic component that resists an electric current by producing a voltage drop between its terminals in accordance with Ohm's law: The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor. Resistors are used as part of electrical networks and electronic circuits.

Identifying resistors Most axial resistors use a pattern of colored stripes to indicate resistance. Surface-mount ones are marked numerically. Cases are usually brown, blue, or green, though other colors are occasionally found such as dark red or dark gray. One can use a multimeter or ohmmeter to test the values of a resistor.

Resistor standards • • • • • • •

MIL-R-11 MIL-R-39008 MIL-R-39017 MIL-PRF-26 MIL-PRF-39007 BS 1852 EIA-RS-279

There are other MIL-R- standards.

Four-band axial resistors Four-band identification is the most commonly used color coding scheme on all resistors. It consists of four colored bands that are painted around the body of the resistor. The scheme is simple: The first two numbers are the first two significant digits of the resistance value, the third is a multiplier, and the fourth is the tolerance of the value. Each color corresponds to a certain number, shown in the chart below. The tolerance for a 4-band resistor will be 2%, 5%, or 10%. The Standard EIA Color Code Table per EIA-RS-279 is as follows: Color 1st band 2nd band 3rd band (multiplier) 4th band (tolerance) Temp. Coefficient

Black Brown Red Orange Yellow Green Blue Violet Grey White Gold Silver None

0 1 2 3 4 5 6 7 8 9

0 1 2 3 4 5 6 7 8 9

×100 ×101 ×102 ×103 ×104 ×105 ×106 ×107 ×108 ×109 ×0.1 ×0.01

±1% (F) ±2% (G)

100 ppm 50 ppm 15 ppm 25 ppm

±0.5% (D) ±0.25% (C) ±0.1% (B) ±0.05% (A) ±5% (J) ±10% (K) ±20% (M)

Note: red to violet are the colors of the rainbow where red is low energy and violet is higher energy. As an example, let us take a resistor which (read left to right) displays the colors yellow, violet, yellow, brown. We take the first two bands as the value, giving us 4, 7. Then the third band, another yellow, gives us the multiplier 104. Our total value is then 47 x 104 Ω, totalling 470,000 Ω or 470 kΩ. Our brown is then a tolerance of ±1%. Resistors use specific values, which are determined by their tolerance. These values repeat for every exponent; 6.8, 68, 680, and so forth. This is useful because the digits, and hence the first two or three stripes, will always be similar patterns of colors, which make them easier to recognize.

Preferred values Main article: preferred number Resistors are manufactured in values from a few milliohms to about a gigaohm; only a limited range of values from the IEC 60063 preferred number series are commonly available. These series are called E6, E12, E24, E96 and E192. The number tells how many standardized values exist in each decade (e.g. between 10 and 100, or between 100 and 1000). So resistors conforming to the E12 series, can have 12 distinct values between 10 and 100, whereas those confirming to the E24 series would have 24 distinct values. In practice, the discrete component sold as a "resistor" is not a perfect resistance, as defined above. Resistors are often marked with their tolerance (maximum expected variation from the marked resistance). On color coded resistors the color of the rightmost band denotes the tolerance: silver 10% gold 5% red 2% brown 1% green 0.5%. Closer tolerance resistors, called precision resistors, are also available. Since some manufacturers may sort resistors into tolerance classes, prudent design of circuits should assess the effect of any or all resistors being at the upper limits of the tolerance range. E12 preferred values: 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82 Multiples of 10 of these values are used, eg. 0.47 Ω, 4.7 Ω, 47 Ω, 470 Ω, 4.7 kΩ, 47 kΩ, 470 kΩ, and so forth. E24 preferred values, includes E12 values and: 11, 13, 16, 20, 24, 30, 36, 43, 51, 62, 75, 91

5-band axial resistors 5-band identification is used for higher precision (lower tolerance) resistors (1%, 0.5%, 0.25%, 0.1%), to notate the extra digit. The first three bands represent the significant digits, the fourth is the multiplier, and the fifth is the tolerance. 5-band standard tolerance resistors are sometimes encountered, generally on older or specialized resistors. They can be identified by noting a standard tolerance color in the 4th band. The 5th band in this case is the temperature coefficient.

Mnemonic phrases for remembering codes There are many mnemonic phrases used to remember the order of the colors. The easiest way to remember the colors is probably to think of the color spectrum, then add in the numbers. Starting at the lowest values, one goes from black (no color) to brownish (infrared) red (2) green (5) to blue (6) and from there to ultraviolet, almost white, and white light. In essence, the higher the energy, the higher the number code. In this way, one learns both the basics of visible light in the electromagnetic spectrum and the color codes. They are, but are not limited to, and variations of: • • • • • • • • • • •

Bye Bye Rose, Off You Go - Birmingham Via Great Western Bad Bacon Rots Our Young Guts But Venison Goes Well. Get Some Now! B.B. ROY of Great Britain had a Very Good Wife, Good Son Buffalo Bill Roamed Over Yellow Grass Because Vistas Grand Were God's Sanctuary Bully Brown Ran Over a Yodeling Goat, Because Violet's Granny Was Gone Snorkeling Buy Better Resistance Or Your Grid Bias May Go Wrong Bad Beer Rots Our Young Guts But Vodka Goes Well Good Sir. Bongo's Buy Randy Ocelot Young Girls Buy Very Groovy Walruses Black Beetles Running Over Your Garden Bring Very Good Weather Black Brown Richard Of York Gave Battle in Vain and the Good Women Grieve Sadly Better Be Right Or Your Great Big Venture Goes Wrong

All of the above are mnemonics for the order: Black Brown Red Orange Yellow Green Blue Violet Gray White (Gold Silver None)

Series and parallel circuits Main article: Series and parallel circuits Resistors in a parallel configuration each have the same potential difference (voltage). To find their total equivalent resistance (Req):

The parallel property can be represented in equations by two vertical lines "||" (as in geometry) to simplify equations. For two resistors,

The current through resistors in series stays the same, but the voltage across each resistor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find their total resistance:

A resistor network that is a combination of parallel and series can sometimes be broken up into smaller parts that are either one or the other. For instance,

However, many resistor networks cannot be split up in this way. Consider a cube, each edge of which has been replaced by a resistor. For example, determining the resistance between two opposite vertices requires matrix methods for the general case. However, if all twelve resistors are equal, the corner-to-corner resistance is 5⁄6 of any one of them.

Fuse (electrical) In electronics and electrical engineering a fuse, short for 'fusible link', is a type of overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows. When the metal strip melts, it opens the circuit of which it is a part, and so protects the circuit from excessive current. A practical fuse was one of the essential features of Edison's electrical power distribution system. An early fuse was said to have successfully protected an Edison installation from tampering by a rival gas-lighting concern. Fuses (and other overcurrent devices) are an essential part of a power distribution system to prevent fire or damage. When too much current flows through a wire, it may overheat and be damaged, or even start a fire. Wiring regulations give the maximum rating of a fuse for protection of a particular circuit. Local authorities will incorporate national wiring regulations as part of law. Fuses are selected to allow passage of normal currents, but to quickly interrupt a short circuit or overload condition.

Fuse characteristics The speed at which a fuse operates depends on how much current flows through it. Manufacturers of fuses plot a time-current characteristic curve, which shows the time required to melt the fuse and the time required to clear the circuit for any given level of overload current. Where several fuses are connected in series at the various levels of a power distribution system, it is very desirable to clear only the fuse (or other overcurrent device) electrically closest to the fault. This process is called "coordination" and may require the time-current characteristics of two fuses to be plotted on a common current basis. Fuses are then selected so that the minor, branch, fuse clears its circuit well before the supplying, major, fuse starts to melt. In this way only the faulty circuits are interrupted and minimal disturbance occurs to other circuits fed by the supplying fuse. Where the fuses in a system are of similar types, simple rule-of-thumb ratios between ratings of the fuse closest to the load and the next fuse towards the source can be used. Fuses are often characterized as "fast-blow" or "slow-blow" or "time-delay", according to the time they take to respond to an overcurrent condition. The selection of the characteristic depends on what equipment is being protected. Semiconductor devices may need a fast or ultrafast fuse for protection since semiconductors may have little capacity to withstand even a momentary overload. Fuses applied on motor circuits may have a time-delay characteristic, since the surge of current required at motor start soon decreases and is harmless to wiring and the motor.

Special Features As visual identification of a blown fuse is only possible when the element is visible ie. glass body fuses, manufacturers have designed a variety of methods to indicate whether the fuse element is intact or blown such as; • • • • • •

Indicating pin: extends out of the fuse cap when the element is blown. Indicating disc: a coloured disc (flush mounted in the end cap of the fuse) falls out when the element is blown. Element window: a small window built into the fuse body to provide visual indication of a blown element. Striker pin: similar to an indicating pin, but extends with more force to trip a switch when the element is blown. Flag: an external sprung arm that is released to an extended position once the elemet is blown. External trip indicator: similar function to striker pin, but can be externally attached (using clips) to a compatible fuse.

Some fuses allow a special purpose microswitch[7] or relay unit to be fixed to the fuse body. When the fuse element blows, the indicating pin extends to activate the micro switch or relay which in turn triggers an event.

Fuse boxes Old electrical consumer units (also called fuse boxes) were fitted with fuse wire that could be replaced from a supply of spare wire that was wound on a piece of cardboard. Modern consumer units contain magnetic circuit breakers instead of fuses. Cartridge fuses were also used in consumer units and sometimes still are, as miniature circuit breakers (MCBs) are rather prone to nuisance tripping. (In North America, fuse wire was never used in this way, although so-called "renewable" fuses were made that allowed replacement of the fuse link. It was impossible to prevent putting a higher-rated or double links into the holder ("overfusing") and so this type must be replaced.) The box pictured is a "Wylex standard". This type was very popular in the United Kingdom up until recently when the wiring regulations started demanding Residual-Current Devices

(RCDs) for sockets that could feasibly supply equipment outside the equipotential zone. The design does not allow for fitting of RCDs (there were a few wylex standard models made with an RCD instead of the main switch but that isn't generally considered acceptable nowadays either because it means you lose lighting in the event of almost any fault) or residual-current circuit breakers with overload (RCBOs) (an RCBO is the combination of an RCD and an MCB in a single unit). The one pictured is fitted with rewirable fuses but they can also be fitted with cartridge fuses and MCBs. There are two styles of fuse base that can be screwed into these units—one designed for the rewirable fusewire carriers and one designed for cartridge fuse carriers. Over the years MCBs have been made for both styles of base. With both styles of base higher rated carriers had wider pins so a carrier couldn't be changed for a higher rated one without also changing the base. Of course with rewirable carriers a user could just fit fatter fusewire or even a totally different type of wire object (hairpins, paper clips, nails etc.) to the existing carrier. In North America, fuse boxes were also often used, especially in homes wired before about 1950. Fuses for these panels were screw-in "plug" type (not to be confused with what the British call plug fuses), in screw-thread holders similar to Edison-base incandescent lamps, with ratings of 5, 10, 15, 20, 25, and 30 amperes. To prevent installation of fuses with too high a current rating for the circuit, later fuse boxes included rejection features in the fuseholder socket. Some installations have resettable miniature thermal circuit breakers which screw into the fuse socket. One form of abuse of the fuse box was to put a penny in the socket, which defeated the overcurrent protection function and resulted in a dangerous condition. Plug fuses are no longer used for branch circuit protection in new residential or industrial construction.

Capacitor A capacitor is an electrical device that can store energy in the electric field between a pair of closely spaced conductors (called 'plates'). When current is applied to the capacitor, electric charges of equal magnitude, but opposite polarity, build up on each plate. Capacitors are used in electrical circuits as energy-storage devices. They can also be used to differentiate between high-frequency and low-frequency signals and this makes them useful in electronic filters. Capacitors are occasionally referred to as condensers. This is considered an antiquated term in English, but most other languages use an equivalent, like the German word "kondensator".

Capacitance The capacitor's capacitance (C) is a measure of the amount of charge (Q) stored on each plate for a given potential difference or voltage (V) which appears between the plates:

In SI units, a capacitor has a capacitance of one farad when one coulomb of charge is stored due to one volt applied potential difference across the plates. Since the farad is a very large unit, values of capacitors are usually expressed in microfarads (µF), nanofarads (nF), or picofarads (pF).

When there is a difference in electric charge between the plates, an electric field is created in the region between the plates that is proportional to the amount of charge that has been moved from one plate to the other. This electric field creates a potential difference V = E·d between the plates of this simple parallel-plate capacitor. The capacitance is proportional to the surface area of the conducting plate and inversely proportional to the distance between the plates. It is also proportional to the permittivity of the dielectric (that is, non-conducting) substance that separates the plates. The capacitance of a parallel-plate capacitor is given by: [1]

where ε is the permittivity of the dielectric (see Dielectric constant), A is the area of the plates and d is the spacing between them. In the diagram, the rotated molecules create an opposing electric field that partially cancels the field created by the plates, a process called dielectric polarization.

Battery (electricity) A galvanic cell is a electrochemical cell that stores chemical energy and makes it available in an electrical form, and a battery is a string of two or more cells in series. Other types of electrochemical cell include electrolytic cells, fuel cells, flow cells, or voltaic cells.[1] Though an early form of battery may have been used in antiquity (the Baghdad Battery), the development of modern batteries started with the Voltaic pile, invented by the Italian physicist Alessandro Volta in 1800.[2] According to a 2005 estimate, the worldwide battery industry generates US$48 billion in sales annually.[3] Formally, an electrical "battery" is a series-connected array of similar voltaic cells ("cells"). However, in many contexts it is common to call a single cell a battery.[4] The two types of batteries, primary and secondary, both convert chemical energy to electrical energy. However, primary batteries can only be used once, as they use up their chemicals in an irreversible reaction. Secondary batteries can be recharged because the chemical reactions they use are reversible; they are recharged by running a current parallel to the battery, with an orientation opposite to the original discharge.[5]

Symbols representing a single Cell (top) and Battery (bottom), used in circuit diagrams.

A Pair of AA Energizer Alkaline Cells

History The earliest known artifacts that may have served as batteries are the Baghdad Batteries, which existed some time between 250 BC and 640 AD. However, it is not known what electrical function they may have served, and if they were in fact batteries at all. Scientists have developed several theories about its use, including medicine (as a painkiller) and electroplating jewelry.[6] The story of the modern battery begins in the 1780s with the discovery of "animal electricity" by Luigi Galvani, which he published in 1791.[7] He created an electric circuit consisting of two different metals, with one touching a frog's leg and the other touching both the leg and the first metal, thus closing the circuit. In modern terms, the frog's leg served as both electrolyte and detector, and the metals served as electrodes. He noticed that even though the frog was dead, its legs would twitch when he touched them with the metals.[8] By 1791, Alessandro Volta realized that the frog could be replaced by cardboard soaked in salt water, employing another form of detection. Having already studied the electrostatic phenomenon of capacitance, Volta was able to quantitatively measure the electromotive force (emf) associated with each electrode-electrolyte interface (voltage) in volts, which were named after him. Such a device is called a voltaic cell, or cell for short. In 1799, Volta invented the modern battery by placing many galvanic cells in series, literally piling them one above the other. This Voltaic Pile gave a greatly enhanced net emf for the combination,[9] with a voltage of about 50 volts for a 32-cell pile.[10] In many parts of Europe batteries continue to be called piles. Unfortunately, Volta did not appreciate that the voltage was due to chemical reactions. He thought that his cells were an inexhaustible source of energy, and that the associated chemical effects (e.g., corrosion) were a mere nuisance -- rather than, as Michael Faraday showed around 1830, an unavoidable by-product of their operation.

Later, researchers placed galvanic cells in series. Such banks of cells are called batteries, presumably after the earlier use by Benjamin Franklin to describe Leyden jars (capacitors) in series and in parallel.[11] Although early batteries were of great value for experimental purposes, their limitations made them impractical for large current drain. Later, batteries, starting with the Daniell cell in 1836, provided more reliable currents and were adopted by industry for use in stationary devices, particularly in telegraph networks where they were the only practical source of electricity, since electrical distribution networks did not exist then.[12] These wet cells used liquid electrolytes, which were prone to leaks and spillage if not handled correctly. Many used glass jars to hold their components, which made them fragile. These characteristics made wet cells unsuitable for portable appliances. Near the end of the 19th century, the invention of dry cell batteries, which replaced liquid electrolyte with a paste made portable electrical devices practical.

How batteries work A battery is a device that converts chemical energy directly to electrical energy.[13] It consists of one or more voltaic cells. Each voltaic cell consists of two half cells connected in series by a conductive electrolyte. Each cell has a positive electrode (cathode), and a negative electrode (anode). These do not touch each other but are immersed in a solid or liquid electrolyte.[14] In a practical cell the materials are enclosed in a container, and a separator between the electrodes prevents the electrodes from coming into contact. Each half cell has a net electromotive force (or emf), with the net emf of the battery being the difference between the emfs of the half-cells, a fact first recognized by Volta. Thus, if the electrodes have emfs , then the net emf is . (Hence, two identical electrodes and a common electrolyte give zero net emf.) Each half cell emf is due to a chargetransferring (or faradaic) chemical reaction at the electrode-electrolyte interface, which transfers charge across the interface. The reaction stops when the charge transfer is enough to cancel out the tendency of the reaction to occur. Non-charge-transferring, or nonfaradaic, reactions can also occur at the interface. These are undesirable, using up the chemicals without producing current (which is the rate of charge transfer). Additional, but relatively ineffective, faradaic reactions (also called parasitic or "side-reactions") can also occur. The electrical potential difference across the terminals of a battery is known as its terminal voltage, measured in volts. The terminal voltage of a battery that is neither charging nor discharging is called the open-circuit voltage, and gives the emf of the battery. The terminal voltage of a battery that is discharging is smaller in magnitude than the open-circuit voltage, and the terminal voltage of a battery being charged is greater than the open-circuit voltage. [15] The voltage developed across a cell's terminals depends on the chemicals used in it and their concentrations. For example, alkaline and carbon-zinc cells both measure about 1.5 volts, due to the energy release of the associated chemical reactions. Because of the high electrochemical potential changes in the reactions of lithium compounds, lithium cells can provide as much as 3 volts or more.

Classification of batteries Batteries are usually divided into two broad classes: •

•

Primary batteries irreversibly transform chemical energy to electrical energy. When the initial supply of reactants is exhausted, energy cannot be readily restored to the battery by electrical means. Secondary batteries can be recharged, that is, have their chemical reactions reversed by supplying electrical energy to the cell, restoring their original composition.[16]

Historically, some types of primary batteries used, for example, for telegraph circuits, were restored to operation by replacing the components of the battery consumed by the chemical reaction. Secondary batteries are not indefinitely rechargeable due to dissipation of the active materials, loss of electrolyte, and internal corrosion.

Power supply A power supply (sometimes known as a power supply unit or PSU) is a device or system that supplies electrical or other types of energy to an output load or group of loads. The term is most commonly applied to electrical energy supplies, less often to mechanical ones, and rarely to others.

Electrical power supplies This term covers the mains power distribution system together with any other primary or secondary sources of energy such as: •

• • • •

Conversion of one form of electrical power to another desired form and voltage. This typically involves converting 120 or 240 volt AC supplied by a utility company (see electricity generation) to a well-regulated lower voltage DC for electronic devices. For examples, see switched-mode power supply, linear regulator, rectifier and inverter (electrical). Batteries Chemical fuel cells and other forms of energy storage systems Solar power Generators or alternators (particularly useful in vehicles of all shapes and sizes, where the engine has rotational power to spare, or in semi-portable units containing an internal combustion engine and a generator) (For large-scale power supplies, see electricity generation.) Low voltage, low power DC power supply units are commonly integrated with the devices they supply, such as computers and household electronics.

Constraints that commonly affect power supplies are the amount of power they can supply, how long they can supply it for without needing some kind of refueling or recharging, how stable their output voltage or current is under varying load conditions, and whether they provide continuous power or pulses. The regulation of power supplies is done by incorporating circuitry to tightly control the output voltage and/or current of the power supply to a specific value. The specific value is closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input. This kind of regulation is commonly categorised as a Stabilized power supply.

Diode In electronics, a diode is a component that restricts the directional flow of charge carriers. Essentially, a diode allows an electric current to flow in one direction, but blocks it in the opposite direction. Thus, the diode can be thought of as an electronic version of a check valve. Circuits that require current flow in only one direction typically include one or more diodes in the circuit design. Early diodes included "cat's whisker" crystals and vacuum tube devices (called thermionic valves in British English). Today the most common diodes are made from semiconductor materials such as silicon or germanium.

History Thermionic and solid state diodes developed in parallel. The principle of operation of thermionic diodes was discovered by Frederick Guthrie in 1873.[1] The principle of operation of crystal diodes was discovered in 1874 by the German scientist, Karl Ferdinand Braun.[2] Thermionic diode principles were rediscovered by Thomas Edison on February 13, 1880 and he took out a patent in 1883 (U.S. Patent 307,031 ), but developed the idea no further. Braun

patented the crystal rectifier in 1899 [1]. Braun's discovery was further developed by Sir Jagdish Bose into a useful device for radio detection. The first radio receiver using a crystal diode was built around 1900 by Greenleaf Whittier Pickard. The first thermionic diode was patented in Britain by John Ambrose Fleming (scientific adviser to the Marconi Company and former Edison employee[2]) on November 16, 1904 (U.S. Patent 803,684 in November 1905). Pickard received a patent for a silicon crystal detector on November 20, 1906 [3] (U.S. Patent 836,531 ). At the time of their invention such devices were known as rectifiers. In 1919 William Henry Eccles coined the term diode from Greek roots; di means 'two', and ode (from odos) means 'path'.

Transistor A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. The transistor is the fundamental building block of the circuitry that governs the operation of computers, cellular phones, and all other modern electronics. Because of its fast response and accuracy, the transistor may be used in a wide variety of digital and analog functions, including amplification, switching, voltage regulation, signal modulation, and oscillators. Transistors may be packaged individually or as part of an integrated circuit, which may hold a billion or more transistors in a very small area.

Importance The transistor is considered by many to be the greatest invention of the twentieth century.[2] It is the key active component in practically all modern electronics. Its importance in today's society rests on its ability to be mass produced using a highly automated process (fabrication) that achieves vanishingly low per-transistor costs. Although millions of individual (known as discrete) transistors are still used, the vast majority of transistors are fabricated into integrated circuits (often abbreviated as IC and also called microchips or simply chips) along with diodes, resistors, capacitors and other electronic components to produce complete electronic circuits. A logic gate consists of about twenty transistors whereas an advanced microprocessor, as of 2006, can use as many as 1.7 billion transistors (MOSFETs) [1]. The transistor's low cost, flexibility and reliability have made it a universal device for nonmechanical tasks, such as digital computing. Transistorized circuits have replaced electromechanical devices for the control of appliances and machinery as well. It is often less expensive and more effective to use a standard microcontroller and write a computer program to carry out a control function than to design an equivalent mechanical control function. Because of the low cost of transistors and hence digital computers, there is a trend to digitize information. With digital computers offering the ability to quickly find, sort and process digital information, more and more effort has been put into making information digital. As a result, today, much media data is delivered in digital form, finally being converted and presented in analog form by computers. Areas influenced by the Digital Revolution include television, radio, and newspapers.

History The first three patents for the field-effect transistor principle were registered in Germany in 1928 by physicist Julius Edgar Lilienfeld, but Lilienfeld published no research articles about his devices, and they were ignored by industry. In 1934 German physicist Dr. Oskar Heil patented another field-effect transistor. There is no direct evidence that these devices were built, but later work in the 1990s show that one of Lilienfeld's designs worked as described and gave substantial gain. Legal papers from the Bell Labs patent show that Shockley and Pearson had built operational versions from Lilienfeld's patents, yet they never referenced

this work in any of their later research papers or historical articles. The Other Transistor, R. G. Arns On 16 December 1947 William Shockley, John Bardeen and Walter Brattain succeeded in building the first practical point-contact transistor at Bell Labs. This work followed from their war-time efforts to produce extremely pure germanium "crystal" mixer diodes, used in radar units as a frequency mixer element in microwave radar receivers. A parallel project on germanium diodes at Purdue University succeeded in producing the good-quality germanium semiconducting crystals that were used at Bell Labs.[2] Early tube-based technology did not switch fast enough for this role, leading the Bell team to use solid state diodes instead. With this knowledge in hand they turned to the design of a triode, but found this was not at all easy. Bardeen eventually developed a new branch of surface physics to account for the "odd" behavior they saw, and Bardeen and Brattain eventually succeeded in building a working device. At the same time some European scientists were led by the idea of solid-state amplifiers. In August 1948 German physicists Herbert F. Mataré (1912– ) and Heinrich Welker (1912– 1981), working at Compagnie des Freins et Signaux Westinghouse in Paris, France applied for a patent on an amplifier based on the minority carrier injection process which they called the "transistron". Since Bell Labs did not make a public announcement of the transistor until June 1948, the transistron was considered to be independently developed. Mataré had first observed transconductance effects during the manufacture of germanium duodiodes for German radar equipment during WWII. Transistrons were commercially manufactured for the French telephone company and military, and in 1953 a solid-state radio receiver with four transistrons was demonstrated at the Düsseldorf Radio Fair. Bell Telephone Laboratories needed a generic name for the new invention: "Semiconductor Triode", "Solid Triode", "Surface States Triode", "Crystal Triode" and "Iotatron" were all considered, but "transistor," coined by John R. Pierce, won an internal ballot. The rationale for the name is described in the following extract from the company's Technical Memorandum calling for votes:

Integrated circuit In electronics, an integrated circuit (also known as IC, microcircuit, microchip, silicon chip, or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) that has been manufactured in the surface of a thin substrate of semiconductor material. A hybrid integrated circuit is a miniaturized electronic circuit constructed of individual semiconductor devices, as well as passive components, bonded to a substrate or circuit board.

Classification Integrated circuits can be classified into analog, digital and mixed signal (both analog and digital on the same chip). Digital integrated circuits can contain anything from a few thousand to millions of logic gates, flip-flops, multiplexers, and other circuits in a few square millimeters. The small size of these circuits allows high speed, low power dissipation, and reduced manufacturing cost compared with board-level integration. These digital ICs, typically microprocessors, DSPs, and micro controllers work using binary mathematics to process "one" and "zero" signals. Analog ICs, such as sensors, power management circuits, and operational amplifiers, work by processing continuous signals. They perform functions like amplification, active filtering, demodulation, mixing, etc. Analog ICs ease the burden on circuit designers by having expertly designed analog circuits available instead of designing a difficult analog circuit from scratch.

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through a shared magnetic field. A changing current in the first circuit (the primary) creates a changing magnetic field; in turn, this magnetic field induces a voltage in the second circuit (the secondary). By adding a load to the secondary circuit, one can make current flow in the transformer, thus transferring energy from one circuit to the other. The secondary induced voltage VS is scaled from the primary VP by a factor ideally equal to the ratio of the number of turns of wire in their respective windings:

By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less. A key application of transformers is to reduce the current before transmitting electrical energy over long distances through wires. By transforming electrical power to a high-voltage, low-current form for transmission and back again afterwards, the transformer allows electricity to be transmitted more efficiently, enabling the economic transmission of power over long distances. Consequently, transformers have shaped the electricity supply industry, permitting generation to be located remotely from points of demand.[1] All but a fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer.[2] Transformers are some of the most efficient electrical 'machines',[3] with some large units able to transfer 99.75% of their input power to their output.[4] Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge gigavolt-ampere-rated units used to interconnect portions of national power grids. All operate with the same basic principles, though a variety of designs exist to perform specialized roles throughout home and industry.

Basic principles The transformer is based on two principles: first, that an electric current can produce a magnetic field (electromagnetism) and, second, that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). By changing the current in the primary coil, one changes the strength of its magnetic field; since the secondary coil is wrapped around the same magnetic field, a voltage is induced across the secondary.

Figure 2: An ideal step-down transformer showing magnetic flux in the core A simplified transformer design is shown in Figure 2. A current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of

very high magnetic permeability, such as iron; this ensures that most of the magnetic field lines produced by the primary current are within the iron and pass through the secondary coil as well as the primary coil.

Induction law The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that

where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and Φ equals the total magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic field strength B and the area A through which it cuts. The area is constant, being equal to the crosssectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer,[5] the instantaneous voltage across the primary winding equals

Taking the ratio of the two equations for VS and VP gives the basic equation[6] for stepping up or stepping down the voltage

Buzzer

Electronic symbol for a buzzer. A buzzer or beeper is a signaling device, usually electronic, typically used in automobiles, household appliances such as a microwave oven, or game shows. It most commonly consists of a number of switches or sensors connected to a control unit that determines if and which button was pushed or a preset time has lapsed, and usually illuminates a light on the appropriate button or control panel, and sounds a warning in the form of a continuous or intermittent buzzing or beeping sound. Initially this device was based on an electromechanical system which was identical to an electric bell without the metal gong (which makes the ringing noise). Often these units were anchored to a wall or ceiling and used the ceiling or wall as a sounding board. Another implementation with some ACconnected devices was to implement a circuit to make the AC current into a noise loud enough to drive a loudspeaker and hook this circuit up to a cheap 8-ohm speaker. Nowadays, it is more popular to use a ceramic-based piezoelectric sounder like a Sonalert which makes a high-pitched tone. Usually these were hooked up to "driver" circuits which varied the pitch of the sound or pulsed the sound on and off.

In game shows it is also known as a "lockout system," because when one person signals ("buzzes in"), all others are locked out from signalling. Several game shows have large buzzer buttons which are identified as "plungers". The word "buzzer" comes from the rasping noise that buzzers made when they were electromechanical devices, operated from stepped-down AC line voltage at 50 or 60 cycles. Other sounds commonly used to indicate that a button has been pressed are a ring or a beep. Some systems, such as the one used on Jeopardy!, make no noise at all, instead using light. Another example is the buzzer at the end of each stage in Sasuke, Kunoichi, and Viking. These buzzers do not make a sound or turn on a light; instead, they stop a nearby digital clock, briefly activate two smoke machines on each side of the stage exit, and open the exit. However, at the end of the Heartbreaker in Viking, the buzzer is replaced with a sword that, when removed, causes two contacts to touch, closing the circuit and causing the latter two actions above to occur. Nowadays some people use the word "buzzer" as to describe a person who's able to create a big buzz around a brand, an event or a company.

Strain gauge A strain gauge (alternatively: strain gage) is a device used to measure deformation (strain) of an object. Invented by Edward E. Simmons in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive, such as cyanoacrylate[1]. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.

The gauge factor GF is defined as where RG is the resistance of the undeformed gauge, ΔR is the change in resistance caused by strain, and ε is strain. For metallic foil gauges, the gauge factor is usually a little over 2[2]. For a single active gauge and three dummy resistors, the output v from the bridge is the bridge excitation voltage.

where BV is

Foil gauges typically have active areas 2-10 mm in size. With careful installation, the correct gauge, and the correct adhesive, strains up to at least 10% can be measured.

Hybrid Integrated Circuit A Hybrid Integrated Circuit, Hybrid Circuit, or simply Hybrid is a miniaturized electronic circuit constructed of individual devices, such as semiconductor devices (e.g. transistors and diodes) and passive components (e.g. resistors, inductors and capacitors), bonded to a substrate or printed circuit board (PCB). Hybrid circuits are often encapsulated in epoxy, as shown in the photo. A hybrid circuit provides the same functionality as a (monolithic) integrated circuit, which in an end-product serves as as a component on a PCB. The difference between the two types of devices is in how they are constructed and manufactured. Some modern hybrid circuit technologies, such as LTCC-substrate hybrids, allow for embedding of components within the layers of a multi-layer substrate in addition to components placed on the surface of the substrate. This technology produces a circuit that is, to some degree, three dimensional. In the early days of transistors, the term Hybrid Circuit was also used to describe circuits where both transistors and vacuum tubes were used simultaneously.

Lamp (electrical component)

A lamp, in technical usage, is a replaceable component such as an incandescent light bulb, which is designed to produce light from electricity. These components usually have a ceramic or metal base, which makes an electrical connection in the socket of a light fixture. This connection may be made with a threaded base, two metal pins, or a "bayonet mount." Re-lamping is the replacement of only the removable lamp in a light fixture.

Types of lamp Incandescent light bulb The incandescent light bulb was the first type of modern electric light, introduced in the early 19th Century it is now being banned in some countries because it is inefficient at converting electricity to light. About 90% of the energy inputed is released as heat. This excess heat is then dumped into the air which, in warm climates, must then be cooled by ventilation or air conditioning, resulting in more energy consumtion. However, in northern climates where heating and lighting is required during the cold and dark winter months, this technology can be considered efficient. Halogen lamps were introduced as an improvement to incandescent bulbs. Visible light output of these lamps is about 15% of the energy input, instead of 10%, allowing them to produce a total of about 50% more light using the same amount of electrical power. The bulb capsule is under high pressure instead of a vacuum or low-pressure noble gas. Good halogen bulbs produce a "cool white" color temperature approaching the appearance of sunlight at noon, while regular incandescent bulbs produce warm light with a warm yellow color temperature. Halogen lamps are usually much smaller than standard incandescents and burn with a hotter filament temperature, which results in a very hot surface. For this reason, a fused-quartz "capsule" is used to enclose the filament, which is sealed behind an additional layer of glass. This is a safety precaution, because halogen "bulbs" can explode if broken while operating or by coming into contact with water or oily residue from fingerprints. The risk of burns or fire is also greater than other bulbs, leading to their prohibition in some places

Fluorescent lamp Fluorescent lamps have an efficiency of about 40%, meaning that for the same amount of light generated, they use ¼ the power and produce 1/6 the heat of a regular incandescent. Fluorescents were limited to linear and a round "circleline" lamp until the 1980s, when the compact fluorescent lamp (CFL) was invented. CFLs can have a built-in electrical ballast which fit into a standard screw base, or make use of a remote ballast. Compact and linear fluorescent lamps last far longer than incandescents, but do have some starting trouble in very cold weather when installed outside.

Fluorescents most often come in cool white (CW), with some home bulbs being a warm white (WW), which has a pinkish color. In between there is an "enhanced white" (EW), which is more neutral. There is also a very cold daylight white (DW). Compact fluorescent lamps are usually considered warm white, though many have a yellowish cast like an incandescent. "Warm" and "cool" are entirely relative terms and almost arbitrary so color temperature and the color rendering index (CRI) are used as absolute scales of color for fluorescents, and sometimes for other types of lighting.

Lamp circuit symbols In circuit diagrams lamps usually are shown as symbols. For example, an electrician would not want to have to keep on drawing out light bulbs so symbols are used instead. There are two main types of symbols, these are:

The X in a circle, which usually represents a bulb not to be mixed up with an L.E.D.

The semi-circled dent in a circle, which usually represents standard filament lamps.

Arc lamp An arc lamp consists of two electrodes which are separated by a gas, including neon, argon, xenon, sodium, metal halide, and mercury. Very high voltage is needed to "ignite" or "strike" the arc. This requires an electrical circuit sometimes called an "igniter", which is part of a larger circuit called the "ballast". After the arc is struck, the internal resistance of the lamp drops to a very low level that would allow an instantly-destructive high current to flow if the ballast were not present to limit it to the lamp's normal operating current. The ballast is typically designed to maintain safe operating conditions and constant light output over the life of the lamp.