Fundamental Electrical and Electronic Principles, Third Edition

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Electromagnetism 191Alternatively, using the inverse of the turns ratio:N2 16I1I2 N 1 25 .so, I 64 . A Ans1Summary of EquationsSelf-induced emf: eN d φd tvoltEmf in a straight conductor: e Bυ sin φ voltForce on a current carrying conductor: F BI sin φ voltMotor principle: T BANI newton metre2 IIForce between current carrying conductors: F 10 71 2newtondVoltmeter figure of merit:1I fsdohm/voltdSelf-inductance: Self-induced emf, e L i dtEnergy stored: W 0.5 LI 2 joulevoltdφNΦL N henryd i IL NSμμN A o rhenry2 2dMutual inductance: Mutually induced emf, e M i 12 voltdtd2N ΦM N2 di I12 21henryM k L1L2 henryEnergy stored: W 0.5L I 0.5 L I MI I joule1 1 2 2 2 2 1 2Transformer: Voltage ratio, V VCurrent ratio, I I2121NNNN2122
192 Fundamental Electrical and Electronic PrinciplesAssignment Questions1 The flux linking a 600 turn coil changes uniformlyfrom 100 mWb to 50 mWb in a time of 85 ms.Calculate the average emf induced in the coil.rotation2 An average emf of 350 V is induced in a 1000turn coil when the flux linking it changes by200 μ Wb. Determine the time taken for theflux to change.SN3 A fl ux of 1.5 mWb, linking with a 250 turncoil, is uniformly reversed in a time of 0.02 s.Calculate the value of the emf so induced.4 A coil of 2000 turns is linked by a magneticflux of 400 μ Wb. Determine the emf induced inthe coil when (a) this flux is reversed in 0.05 s,and (b) the flux is reduced to zero in 0.15 s.5 When a magnetic flux linking a coil changes,an emf is induced in the coil. Explain thefactors that determine (a) the magnitude ofthe emf, and (b) the direction of the emf.6 State Lenz ’ s law, and hence explain the term‘ back emf ’ .7 A coil of 15 000 turns is required to producean emf of 15 kV. Determine the rate of changeof flux that must link with the coil in order toprovide this emf.8 A straight conductor, 8 cm long, is movedwith a constant velocity at right angles toa magnetic field. If the emf induced in theconductor is 40 mV, and its velocity is 10 m/s,calculate the flux density of the field.9 A conductor of effective length 0.25 m ismoved at a constant velocity of 5 m/s, througha magnetic field of density 0.4 T. Calculate theemf induced when the direction of movementrelative to the magnetic field is (a) 90°, (b) 60°,and (c) 45°.10 Figure 5.44 represents two of the armatureconductors of a d.c. generator, rotating in aclockwise direction. Copy this diagram andhence:(a) Indicate the direction of the field pattern ofthe magnetic poles.An armature is the rotating part of a d.c. machine.If the machine is used as a generator, it containsthe coils into which the emf is induced. In the caseof a motor, it contains the coils through whichcurrent must be passed, to produce the torqueFig. 5.44(b) Indicate the direction of induced emf ineach side of the coil.(c) If this arrangement was to be used as amotor, with the direction of rotation asshown, indicate the direction of currentflow required through the coil.11 A conductor of effective length 0.5 m is placedat right angles to a magnetic field of density0.45 T. Calculate the force exerted on theconductor if it carries a current of 5 A.12 A conductor of effective length 1.2 m is placedinside a magnetic field of density 250 mT.Determine the value of current flowingthrough the conductor, if a force of 0.75 N isexerted on the conductor.13 A conductor, when placed at right angles to amagnetic field of density 700 mT, experiencesa force of 20 mN, when carrying a current of200 mA. Calculate the effective length of theconductor.14 A conductor, 0.4 m long, lies between twopole pieces, with its length parallel to the polefaces. Determine the force exerted on theconductor, if it carries a current of 30 A, andthe flux density is 0.25 T.15 The coil of a moving coil meter is woundwith 75 turns, on a former of effective length2.5 cm, and diameter 2 cm. The former rotatesat right angles to the field, which has a fluxdensity of 0.5 T. Determine the deflectingtorque when the coil current is 50 μ A.16 A moving coil meter has a coil of 60 turnswound on to a former of effective length22.5 mm and diameter 15 mm. If the fluxdensity in the air gap is 0.2 T, and the coilcurrent is 0.1 mA. Calculate (a) the force actingon each side of the coil, and (b) the restoringtorque exerted by the springs for the resultingdeflection of the coil.
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Fundamental Electrical and Electron
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Fundamental Electricaland Electroni
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ContentsPreface ...................
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Contents vii5.12 Figure of Merit an
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PrefaceThis Textbook supersedes the
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IntroductionThe chapters follow a s
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Chapter 1Fundamentals1.1 UnitsWhere
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Fundamentals 3where the ‘ k ’ i
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Fundamentals 5Since the basic unit
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Fundamentals 7S (mm)positiveslopene
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Fundamentals 9All materials may be
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Fundamentals 11Fig. 1.6Potential Di
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Fundamentals 13flow. Now, this pose
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Fundamentals 15then current I will
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Fundamentals 17(b)VR ohmI11. 55so,
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Fundamentals 19Note: Since P VI wa
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Fundamentals 21and distributed by t
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semiconductorFundamentals 23R (Ω)c
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Fundamentals 25PLEASE NOTE that the
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Fundamentals 27units. Another advan
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Fundamentals 29approved graph paper
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Chapter 2D.C. CircuitsLearning Outc
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D.C. Circuits 33(a)(b)(c)R R 1 R
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D.C. Circuits 35so V BC 8 VI V am
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D.C. Circuits 37In this context, th
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D.C. Circuits 39E 12 V; R 1 6 Ω
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D.C. Circuits 41Applying the potent
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D.C. Circuits 43more parallel resis
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D.C. Circuits 45R AC R AB R BC oh
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D.C. Circuits 47(b) The circuit has
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D.C. Circuits 49Worked Example 2.8Q
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D.C. Circuits 51that there are only
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D.C. Circuits 53BCDEB :42I 10( I I)
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D.C. Circuits 55Substituting this v
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D.C. Circuits 57As a check that the
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D.C. Circuits 59B(I 1 I 3 )6 Ω 4
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D.C. Circuits 61V I R and V I RAB
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D.C. Circuits 63BI 1(I 1 I 3 )R 1R
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D.C. Circuits 65From the above exam
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D.C. Circuits 67has been replaced b
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D.C. Circuits 69Assignment Question
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D.C. Circuits 71Assignment Question
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D.C. Circuits 732 Reverse the polar
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Chapter 3Electric Fields andCapacit
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Electric Fields and Capacitors 77Q
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Electric Fields and Capacitors 79He
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Electric Fields and Capacitors 81re
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Electric Fields and Capacitors 83Wo
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Electric Fields and Capacitors 85pe
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Electric Fields and Capacitors91C 1
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Electric Fields and Capacitors933
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Electric Fields and Capacitors 95(d
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Electric Fields and Capacitors 97AN
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Electric Fields and Capacitors 1013
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Electric Fields and Capacitors 103P
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Electric Fields and Capacitors 105E
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Electric Fields and Capacitors 107A
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Electric Fields and Capacitors 109A
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Chapter 4Magnetic Fields andCircuit
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Magnetic Fields and Circuits 113dis
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Magnetic Fields and Circuits 115INF
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Magnetic Fields and Circuits 117Wor
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Magnetic Fields and Circuits 1194.8
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Magnetic Fields and Circuits 121A
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Magnetic Fields and Circuits 123How
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Magnetic Fields and Circuits 125For
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Magnetic Fields and Circuits 127FI
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Magnetic Fields and Circuits 129the
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Magnetic Fields and Circuits 131S2s
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Magnetic Fields and Circuits 133B(T
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Magnetic Fields and Circuits 135Φ
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Magnetic Fields and Circuits 137Ass
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Magnetic Fields and Circuits 139Met
Page 154 and 155: Chapter 5ElectromagnetismLearning O
Page 156 and 157: Electromagnetism 143When the magnet
Page 158 and 159: Electromagnetism 145moved verticall
Page 160 and 161: Electromagnetism 147Worked Example
Page 164 and 165: Electromagnetism 151IeIeRFig. 5.11I
Page 168 and 169: Electromagnetism 155rFig. 5.16an ef
Page 170 and 171: Electromagnetism157Now, flux densit
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Page 174 and 175: Electromagnetism 161Fig. 5.22Dampin
Page 178 and 179: Electromagnetism 165Coil resistance
Page 180 and 181: Electromagnetism 16712 V30 kR 1V70
Page 182 and 183: Electromagnetism 169R110 1V1 V 0vo
Page 184 and 185: Electromagnetism 171‘ zeroed ’
Page 186 and 187: Electromagnetism 173Fig. 5.36the in
Page 188 and 189: Electromagnetism 175Similarly, when
Page 190 and 191: Electromagnetism 177The self-induce
Page 192 and 193: Electromagnetism 1795.19 Factors Af
Page 194 and 195: Electromagnetism 181This emf may al
Page 196 and 197: Electromagnetism 183the above equat
Page 198 and 199: Electromagnetism 185but, energy sto
Page 200 and 201: Electromagnetism 187a common iron c
Page 202 and 203: Electromagnetism 189dΦdtand d Φdt
Page 206 and 207: Electromagnetism 193Assignment Ques
Page 208 and 209: Electromagnetism 195Suggested Pract
Page 210 and 211: Chapter 6Alternating QuantitiesLear
Page 212 and 213: Alternating Quantities 199e(V)1.0E
Page 214 and 215: Alternating Quantities 201emf (V)0T
Page 216 and 217: Alternating Quantities 203(b) 3575
Page 218 and 219: Alternating Quantities 205(b) v 55
Page 220 and 221: Alternating Quantities 207Worked Ex
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Page 226 and 227: Alternating Quantities 213(b)I fsd
Page 228 and 229: Alternating Quantities 215Although
Page 230 and 231: Alternating Quantities 217of using
Page 232 and 233: Alternating Quantities 2196.14 Addi
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Page 238 and 239: Alternating Quantities 225glass tub
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Page 246 and 247: Chapter 7D.C. MachinesLearning Outc
Page 248 and 249: D.C. Machines 235Assuming no fricti
Page 250 and 251: D.C. Machines 237E (V)0t (s)Fig. 7.
Page 252 and 253: D.C. Machines 239for the field wind
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D.C. Machines 241shown in Fig. 7.12
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D.C. Machines 243increase with the
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I fR fR aD.C. Machines 245I LI aVE
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D.C. Machines 247would be infinite!
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Chapter 8D.C. TransientsLearning Ou
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D.C. Transients 251Having confirmed
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D.C. Transients 253For such a CR ci
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D.C. Transients 255Note: The time c
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D.C. Transients 257can conclude tha
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D.C. Transients 259(a)initial d idt
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D.C. Transients 261Assignment Quest
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Chapter 9Semiconductor Theoryand De
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Semiconductor Theory and Devices 26
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Appendix APhysical Quantities with
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Answers to Assignment QuestionsChap
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Answers to Assignment Questions 287
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IndexAbsolute permeability , 119Abs
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Index 291Peak factor , 206Peak valu
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Fundamental Electrical and Electronic Principles, Third Edition

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