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FIRST MULTICOLOUR EDITION A TEXTBOOK OF ELECTRICAL TECHNOLOGY VOLUME I BASIC ELECTRICAL ENGINEERING IN S.I. SYSTEM OF UNITS A. I “my Illusmnnmnmou lei TEXTBOOK OF. ' E 5c ICAL. TEC oosv. IN S.l. UNITS. Volume II. AC 81 DC MACHINES. homeranking.infoA THERAJA. E g1. S BllﬂNll. Fourth Edition/Revision, (entitled Timeless Secrets of Health and Testing Your Mind/Body Response. 3 The Wonders Of O.

Sucb circuits can be easily solvedwithtbebelpofKircbhofl's lawswbicbaretwoinnumber I. Theendsofamid-eanhed resistorhaveopposite polarity. Fill Intheblanks a 2. At point B, th. S Fig. Circuit- DTI.

Increasing the applied voltage does produce more current but it does not increase in the same proportion as V.

Example 1. Calcula1e I potential ofpoint A w. Hence, potential ofpointA w. Work and Power Work and energy are the same thing but power is. Suppose,a battery ofVvolts drives a current ofIamperesthrough a resistanceofRohms for t seconds.

Another unit often employed in Semiconductor Physics is electron-volt eV. It is equal to the amount of work needed to move an el. Since, there are 6. The electric power required to maintain thiscunent is W. What should be thepowerraring ofthe resistor?

Hence, a resistorof 5 W power rating VOuld be most suitable. Cells in Series and Parallel Electriccells may be connected eitherinseriesorinpar-allel to form barreries. Eachof these combinations has a different value ofthe total voltage and current-delivering capacity. SeriesConnection 6V In Fig.

ParallelConnection Such a combination is used when the purpose is to obtain morecurrent thanis availablefromasingle unit.

As shown in Fig. Incase, cellsof different emf's are connected in series, the current deliveringcapacity ofsuch a combination is equal tothatof thesinglecellwhichhas the lowest current-delivering capacity. Such connections are frequently found in many circuits including those in radio and television receivers. Find the potential ofpoints i Cand ii Din Fig.

Whalis thedirectionofcurren1flow through CD?

C D Fig. Compute lhe po1ential of poin1 i A and ir C. What is the p. Find lhcreadingofthe milliam. Compute the valueofresistorR in Fig. Whatwouldbethe voltageacrosspointsA andBinseries-parallelcombinationofFig. Find the magnitude anddirection ofcurrent in Fig. In the seriescircuitofFig. What isthep. Which pointisaLahigher potential: Bor C?

Fillin theblanksby most appropriateword s or numerical vaJues s. Chassis ground is assumed to have Ohm's lawgives relationship betweenapplied voltage, current and The resistance ofa circuit is equal to voltage dividedby Linear resistor is one whose Tungsten filament of an electric bulb repre- sentsan examples of Wattage ofadevice is given by theproductof Electron-volt is the unitof For getting more current.

Theendsofamid-eanhed resistorhaveopposite polarity. Groundis always alO V. A long and straight wire is called a linear resistor.

Anon-linearresis1orisone whosecurrent does not very linearly with its voltage. Whenafewsimilarcellsareconneclcdin series, current is increased proportionately. Parallelcombinationofcellsisusedwhenmore currentis needed. Series-Parallelgrouping ofcells providedmore power. Multiple ChoiceItems l. Inanelectroniccircuit;commonreferencepoint a is always thenegativebattery tenninal b is always the most positive point c is always the most negative point d maybe any point 2.

The 1erm 'ground' spoken in connection with an electroniccircuit means a adirectconnectiontoearthlhrough awire b acommonconnection for allcomponents c a shon circuil d negative battery terminal 3. Fordoublingthecurrentina circuitofconstant resistance,the applied voltagemust be a kept thesame b doubled c halved d quadrupled 4. Each cell supplies Elec1r0n-volt is the unit of a voltage b energy c current d power 6.

Thecurrentflowing throughthe PNP transistor of Fig. Fill Intheblanks a 2. A nresistoris tobeusedin acircuitcarrying a current of 0. Its power rating should be A linearresistor isdefinedasa resistor a whose value is independent of applied voltage b. True or False I. Multiple Choice Items l. The three resistorsR. The result is onlyone path for current flow. Due Lo this current flow, vol. Series Circuit 2.

Total Power 4. Series Voltage Dividers 6. Parallel Circuits 9. Laws of Parallel Circuits Special Case of Only Two Branches Any Branch Resistance Proportional Current Formula Series-Parallel Circuits In this diagram, the negative battery terminal has been grounded even t.

Characteristics of a Series Circuit A series resistive network has the following characteristics 1. Total resistance equals the st1 ofallseries resistances. In the Fig.

C Fig. CUllent through all resistors istlte same. Tire sun, ofindividual JR drops equals tlu applied voltage. As seen from Fig. There is a stepped fall in voltage as we go from one end the battery to theother as shown in Fig. Polarity of IR Drops The study of voltage polarities, whether positive or negative, is of extreme importance in transistor and semiconductor circuits.

When voltage drop exists across a resistor, its one end mustbe Otherwise, without a potential difference, no current could flow through the resistance to produce the LR drop. The polarity of this drop can be associated with thedirection of cunentflow. Ifcurrent enters a resistor at point A and goes out from point8, then A must be at a higher potential than 8.

In other words, A must be positive with respect to8.

Total Power The power needed to drive cunent through different resistors appears in the form of heat. Hence, total power supplied by the energy source must be equal to the sum ofindividual powers dissipated in different resistors. Series-Aiding and Series-Opposing Voltages In series-aiding combination, the voltage sources ceUs or batteries are connected in series such that positive terminal ofone is joined to the negative terminal ofthe next. IIn series-opposing combination, 1.

In this case, the net voltage is the difference of the two voltages and has the same polarity as the larger of the two voltages.

With reference 10 the circuitofFig. Power is supplied by 12 V battery only and none by 6 V banery. In fact, 6 V battery consumes poweras explained below. Power supplied by 12 Vbatteryis - 12 X 0. Question is: It has been consumed by lhe 6V battery. Remember that power is needed to drive current against an opposing voltage. So,outofthe 6 W input power, 3 W are dissipated by the tworesistors and 3 W are consumed by the 6V battery. Also Example 2. Forthe circuit ofFig. Proportional Voltage Formula in a Series Circuit In a series circuit, voltage drop varies directly with resistance.

Hence, a simplerelation can be found to calculate individual voltage drops without first finding the circuit current In Fig. I 1 a is shown a 24 V batteryconnected across a series combination ofthree resistors, R. Current flowingthrough the resistorsgives rise to voltage drops proportional to their resistances. These voltages can be used for loads needing voltages less thanthebattery voltage. A typical example iswhen we use a single power supply Vcc to provide collector voltage and bias voltage for transistor bias circuit as shown in Fig.

As Now, wehaveachoiceofthreevoltages: Ifwewant 75 V, thepick offpoints areA andB. Ifweneed 25 V, it isavailablebetween pointsB and C. Ofcourse, I00V is available between points A and C. Now, takethe tranSistor biasing circui1 ofFig. Here, collector voltage required is 9 Vbut basebiasvoltage required is 3 V. A simple series voltagedividernetwork R1 -R2 is added to supply the two required voltages from a single source.

As seen, total voltageacrossR1 - Rz is9V. Example 2. Voltage dilllder circuit board. The maximum currentwhich the battery cansupply is 60 ,nA. Ifthe circuit becomes open anywhereas shown in Fig. First, the 'open' will offer aninfiniteresistance. Hence, circuit current will become: Consequently, there would be no voltagedrops across RI and R2.

Second, whole of the applied voltage wo11ld be felt across the 'open'. Hence, it causes the problem of excessive current which, in tum, causes power to increase many times and circuit components tobum out. Soldersplash wire. Now, total circuit res. Hence, there should be afuse which should open ifthere is too much current in the circuit.

Parallel connections are also called multiple. A very important feature of Branches parallel circuits, as compared toseries circuiu.

Hence, ifany load i. Voltage acrosseurh brunch h the san1e For example, in Fig. Reciprocal resistance formula Accordingto this formula,thereciprocalofthe net orequivalent resistance oftheentire circuit equals the sum ofthereciprocalsoftheindividual resistances.

Hence eochheadlight isexposedtothefull potentlat difference supplied by the car's electrical system, giving maximum brightness. One headlight burns out. Talking in terms of conductances, it means that - - I A. The sumof branch currents is equal to the total current supplied bythe battery As seen from Fig. Special Case of Equal Resistances in all Branches If resistances in all branches ofa parallelcircuit are equal, then combinedresistance equals the value ofone branch resistance divided by the number of branches.

Ifthere were four such res. In fact, as we keep adding more branch resistances, the total resistance keeps on decreasing. A However, it shoula become quite clear if one realizes that each resistor provides anadditionalcurrent path and thus increases the total current. Now, with a constant voltage, an increase in current can only mean a decrease in circuit resist. It is seen that combinationoftwo parallel resistances is equal to their product divided by their sum.

Any Branch Resistance A It can be verified that combined or equivalent resistance of a parallel circuit is less than the least amongst them. Fromexample, inFig. Proportional Current Formula Current is inversely proportional to resistance. Hence, current through each branch ofa parallel circuit[Fig.

A 12 Vbattery ofnegligible internal resistance is coected across aparallel combination of4 K, 6Kand 12 K resistors asshown in Fig. Compute I. As shown inFig. Bui fuU , applied voltage is available across the 'open'. However, as the other two bulbs remain connected across the voltage supply, they would keep operating normally. It may be noted that if a voltmeter is connected across the openbulb, it wiU read full supply voltage of V.

Duetothis excessivecurrent,the wires may get hotenoughtobum outunless thecircuit isprotected by a fuse. Following points are worth noting Ci Iftherewere three bulbs, they willnotglow. D Fig. Series-Parallel Circuits Series-parallel circuits are used where it is necessary to provide various amounts ofcurrent and voltages withsinglepowersupply.

ElectroniccircuitsareusuaUyofthis typebecausetheygenerally use onJy one voltage source. In such circuits, some resistors are connected in parallel and then this parallel combination is connected inseries with otherresistors as shown in Fig.

Analysing Series-Parallel Circuits In most ofthesituations, itishelpful to reducethegivencircuitto an equivalentseriescircuit Thiscan bedoneby firsthandlingtheparallel partofthecircuit and then reducing it to an equivalent single resistance asshown inFig. Second step is to find total resistance by addition.

The effect of an 'open' would be explained with the help of Fig. This is in series with R1. Now, let us considerthe effect ofopening the switch as in Fig. Moreover,point CinFig. Coosequently, p. Depending on where it occurs, it can cbaoge all tile current aod voltage values in tile circuit.

Let us calculate the nom1al current aod voltagevalues etc. It not only shorts outRibut R3 aswell therebyreducing thegivencircuittothe seriescircu.

One can analyse it from any point by looking at thepath or paths to the ground.

I 12V V It is seen that I. First, let us simplify parallel circuit CD. VAB - 20x 0. Find the currentand voltage drop acrosseach resistor in Fig. We will uselaws ofseries and parallel combination and start from point Dupwards to point A.

Asseen, there are two 4K resistors in parallel across point C or D andground G. Hence, Reabecomes zeroas shown in Fig. A tapped voltage divider is to be connected across a V de supply to provide outputsof a 15 mA at I00Vand b 20 mA at V.

Find the resistance ofeach section of the divider; itspowerdissipation andtotal resistance ifthebleedercurrentpassedby the divideristo be 60nlA. The divider circuit is shown in Fig. In the circuit ofFig. Calculate vollage drops across the three series-connected resistors in Fig. All values are in kilohm. In the series network ofFig. How will these values change ifa shon is placed, between points A and B? AJIresislallces are in kilohm. All resistance values are in kilohm.

In the series voltage-dividercircuit of Fig. Calculate the values of resistances R1 and R2 and their power ratings. In the networkof Fig. In thecircuitofFig.

How doyouaccount forthe fact thatpower supplied by 12 V battery is more than the sum ofpowers dissipated by the three resistors. A Fig. Calculate the variousbranchcurrentsofthe circuit shown in Fig. Allresistance valuesare in ohms. Resistorsare saidtobeconnectedin serieswhen Aseriesnetworkorresistors usedforproviding different voltages from a singlevoltage source is called The total resistance of a paraUel circuit is always CeUsareconnectedinserieswhen higher Ifmore current is required, then cells may be joined in When both higher voltage and higher current are required,ceUs may be joined in Answer True orFalse I.

Ifsame amountorcurrent passes through each resistor or a combination, they must be connectedin series. A 'shon' anywhere in parallel circuit leads to excessivepowerdemandon thesourceofenergy supply. The combined resistanceof aparallel circuiti. Used this for a couple of courses.

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