Practical Electricity: A Laboratory and Lecture Course for First Year Students of Electrical Engineering, Based on the International Definitions of the Electrical Units, Volume 1

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Cassell, limited, 1897 - Electricity - 643 pages
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Contents

Relative Advantages of Voltameters and Galvanometers
42
Meaning of the Relative and the Absolute Calibration of a Galvanometer
45
Experiment for Calibrating a Galvanometer Relatively or Absolutely
46
Graphically Recording the Results of an Experiment
50
Practical Value of Drawing Curves to Graphically Record the Results of Experiments
55
To Construot a Galvanometer Scale from which the Relative Strengths of Currents can be at once Ascertained
58
GALVANOMETERS AND AMMETERS 16 Distribution of Magnetism in a Permanent Magnet
63
Magnetic Poles
67
Why a Galvanometer Needle has a Given Deflection for a Given Current
69
Mapping out Lines of Force
71
Comparing the Relative Strength of the Different Parts of a Magnetic Field
79
Tangent Galvanometer
83
Adjusting the Coil of a Tangent Galvanometer
85
SECTIOK PAGE 24 Scale for a Tangent Galvanometer
87
Tangent Law
91
Variation of the Sensibility of a Tangent Galvanometer with the Number of Windings and with the Diameter of the Bobbin
95
Values in Amperes of the Deflections of a Tangent Galvano meter controlled only by the Earths Magnetism
102
Magnetometer
107
Calibrating any Galvanometer by Direct Comparison with a Tangent Galvanometer
108
Pivot and Fibre Suspensions
110
Sine Law
111
Employment of the Sine Principle in Galvanometers
118
Construction of Galvanometers in which the Angular Deflec tion is directly Proportional to the Current
124
Galvanometers of Invariable Sensibility
127
Permanent Magnet Ammeter
130
Magnifying Spring Ammeter
135
Gravity Control Ammeters
138
Moving Coil Ammeters
144
Moving Coil Ammeter with Magnetic Control
150
DIFFERENCE OF POTENTIAL AND RESISTANCE 40 Difference of Potentials
152
and Negative Potentials
160
Electrometer
162
Ohms Law
167
Resistance
172
Ohm
173
Volt
174
Current Method of Comparing P Ds
176
Reason for Using High Resistance Galvanometers for P D
178
Voltmeter
179
Ammeters used as Voltmeters
181
Moving Coil Voltmeter 18
183
Voltmeters used as Ammeters
188
GoldLeaf Electroscope
191
Sensibility of GoldLeaf Electroscopes
194
No Force Inside a Closed Conductor Produced by Exterior Electrostatic Action
196
Potential due to Exterior Electrostatic Action is Uniform at all Points Inside a Closed Conductor
197
Voltmeters must be Enclosed in a Conducting Case
198
The Potential of a Conductor
200
relatively to other Bodies
201
The Potential of a Body Depends Partly on its Size and Shape
204
the Quantity of Electricity
206
No Electricity at Rest Inside a Conductor
209
Comparing Quantities of Electricity
211
Quantity of Eleotricity Produced by Rubbing Two Bodies Together
214
Conduction and Induction
218
Testing the Sign of the Electrification of a Body
221
Screening Outside Space from Inside Electrostatic Action
222
Electric Density
224
Examples Showing the Difference between Potential Quan tity and Density
226
CHAPTER IV
232
Ohmmeter
233
Simple Substitution Method of Comparing Resistances
235
Differential Galvanometer
238
its Principle
241
its Use and Simple Method of Constructing
245
Bridge Key
250
Use of a Shunt with the Bridge
252
Meaning of the Deflection on a Bridge Galvanometer
253
Variation of Resistance with Length
254
Variation of Resistance with CrossSection
257
Resistance of Metals and Alloys for a Given Length and Weight
260
Portable Forms of Wheatstones Bridge
285
Calibrating a Galvanometer by using Known Resistances and a Constant P D
287
Shunts
289
Multiplying Power of a Shunt
290
Combined or Parallel Resistance
291
Currents in Parallel Conductors
295
Increase of the Main Current Produced by Applying a Shunt
298
Principle of Universal Shunts
303
Method of Constructing a Universal Shunt Box and its Advantages
304
Use of Shunts with a Differential Galvanometer
311
CHAPTER V
313
Joule
317
Heat Produced by a Current
318
Measuring the Rate of Production of Heat by a Current
319
Power
325
Watt
326
its Principle
328
Commercial Forms of Wattmeters
331
Clock Form
334
Motor Form
341
Board of Trade Unit of Energy
349
Electric Transmission of Energy
352
Power Developed by a Current Generator
358
Electromotive Force of a Battery
359
Connection between the E M F of a Battery the P D
364
Electromotive Force of any Current Generator
369
Power Absorbed in the Circuit Exterior to the Generator Back E M F
370
Distribution of Potential in a Battery
374
A Current Generator may Abstract Energy from a Circuit even when its E M F Helps the Current
381
External Circuit that Receives Maximum Power from a Given Current Generator
385
Arrangement of Part of the External Circuit to Receive Maximum Power
393
Way in which Power Received by External Circuit Varies from Maximum
397
Efficiency
404
Efficiency of Electric Transmission of Energy
408
Connection between Electrical Efficiency of Transmission and Ratio of the Power Received to the Maximum Power Receivable
412
CHAPTER VI
418
TwoFluid Cell
423
Local or Prejudicial Action
428
Gravity DanieUs Cells
431
Minottos Cell
433
Resistance of Daniells Cells
434
Groves Cell
438
Bunsens Cell
443
Potassium Bichromate Cell
445
Leclanche Cell
449
Dry Cells
457
Hellesen Dry Cell
458
Burnley or E O O Dry Cell
459
Obach Dry Cell
460
EdisonLalande Cell
462
Clarks CeU
466
Temperature Variation of the E M F of the Clarks Cell
475
Calculation of the E M F of a Cell from the Energy Liberated by the Chemical Action
477
Cost of Producing Electric Energy with Galvanic Cells and with a Dynamo Compared
482
Measuring a Cells Resistance when Very Small
492
Measuring a Cells Resistance when Not Very Small
493
15L Remarks on the Preceding Methods of Measuring the Resistance of Cells
498
Comparing the Electromotive Forces of Cells
502
Poggendorffs Method of Comparing Electromotive Forces
507
Potentiometer Method of Testing the Accuracy of a Volt meter Scale
510
Fosters Method of Subdividing a Wire into Lengths having Equal Resistances
513
Potentiometer Method of Graduating a Voltmoter in terms of the E M F of a Clarks Cell
516
Use of a Clarks Cell and a Known Resistance as a Standard of Current
519
Calibrating a Galvanometer by using Known Resistances and a Cell of Constant E M F
521
Constant P D and Constant E M F
522
Independence of Currents in Parallel Circuits
525
Arrangements of Cells
536
Mercury Switchboard for Batteries
539
Arrangement of a Given Number of Cells to produce the Maximum Current through a Given External Resistance
545
Minimum Number of Cells Required to Produce a Given Current and P D
549

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Page 591 - Ampere, which is one-tenth of the unit of current of the CGS system of electromagnetic units and which is represented sufficiently well for practical use by the unvarying current which, when passed through a solution of nitrate of silver in water, in accordance with a certain specification, deposits silver at the rate of 0.001118 of a gramme per second.
Page 585 - As a unit of resistance, the international ohm, which is based upon the ohm equal to 10" units of resistance of the CGS system of electromagnetic units, and is represented by the resistance offered to an unvarying electric current by a column of mercury at the temperature of melting ice, 14.4521 grams in mass, of a constant cross-sectional area and of the length of 106.3 centimetres.
Page 587 - ... the electromotive force that, steadily applied to a conductor whose resistance is one international ohm, will produce a current of...
Page 586 - The unit of current shall be what is known as the international ampere, which is one-tenth of the unit of current of the centimeter-gramsecond system of electro-magnetic units, and is the practical equivalent of the unvarying current, which, when passed through a solution of nitrate of silver in water in accordance with standard specifications, deposits silver at the rate of one thousand one hundred and eighteen millionths of a gram per second.
Page 466 - ... carefully removing any loose pieces of the zinc. Just before making up the cell dip the zinc into dilute sulphuric acid, wash with distilled water, and dry with a clean cloth or filter paper.
Page 466 - Mix the washed mercurous sulphate with the zinc sulphate solution, adding sufficient crystals of zinc sulphate from the stock bottle to ensure saturation, and a small quantity of pure mercury. Shake these up well together to form a paste of the consistence of cream. Heat the paste, but not above a temperature of 30 C.

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