Electricity for Public Schools & Colleges

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Longmans, Green, & Company, 1903 - 451 páginas

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Contenido

Use of Keepers
9
Methods of Magnetisation
10
Failure of a Smees Cell to Decompose Water
11
MECHANICAL AND MAGNETIC UNITS 1 Introductory 4 Force ه ه ب به 2 Fundamental and Derived Units
12
Velocity and Acceleration 5 Parallelogram of Forces c
13
Moments and Couples
14
Magnetic Fields and Unit Fieid
15
Magnetic Moment of Practical not Ideal Magnets
16
Magnetic Curves
17
Magnetic Induction takes place along the Lines of Force
19
CHAPTER III
20
Use of Torsion Balance at constant angle
21
Series Arrangement of Arc Lamps
23
Method of Oscillations
24
SECTION PAGR 4 Laws of Magnetism
26
Proof of Law II by Torsion Balance
27
Measurements as affected by Induction
28
Compasses
29
Modification of Earths Lines of Force by the Presence of Iron Masses
30
Measurement of Declination
31
Resolution of Earths total Field into two or three Components
34
To find the Inclination or Dip
36
Measurement of the Earths Magnetic Elements
37
The Method of Deflexions
38
Magnetometers Changes in the Earths Field
40
THE SIMPLER PHENOMENA OF ELECTROSTATICS 1 Introductory
42
Dryness needed not High Temperature
43
Conductors and NonConductors
44
Electrics and NonElectrics
45
The two sorts of Electrification are always produced together
46
Equal Quantities of the opposite Electrifications are always pro duced simultaneously
47
The Fluid Theories of Electricity
48
The three Laws of Electrostatics
49
Law II The Force varies as Q x Q
51
First Ideas as to Induction
52
PAGE
53
First Ideas as to Distribution
55
Faradays Icepail illustrating the Laws of Distribution and of Induction
57
Electrophorus
59
Frictional Electric Machines
60
Miscellaneous Experiments with the Electrical Machine
63
INTRODUCTORY CHAPTER ON POTENTIAL SECTION PAGE 1 Quantity of Electrification
65
Electrical Level or Electrical Potential
66
Measurement of differences of Electrical Level by Work
67
Elementary Ideas on Capacity
68
Lines of Force and Equipotential Surfaces
69
Induction from a Potential Point of View
70
Necessity of distinguishing Sign of Charge and Sign of Potential
74
CHAPTER VI
76
Experiments with the two Condenser Plates
78
Discussion of the Terms Bound and Free
81
Conditions Affecting the Magnitude of the Bound Charge
82
An Isolated Body considered as the Limiting Case of a Condenser
83
Leyden Jars
85
The Unit Jar
86
Cascade arrangement of Leyden Jars
88
Nature of the Leyden Jar Charge
90
Various Effects of the Discharge
91
Induction Effects of the Discharge
94
Wheatstones Sparkboard
96
The Condensing Electroscope
98
CHAPTER VII
100
Application to Induction Machines
102
Varleys Induction Machine
103
Sir W Thomsons Replenisher
104
The Voss Machine
105
The Holtz Machine
108
CHAPTER IX
121
ELECTROSTATIC POTENTIAL
127
Equipotential Surfaces
133
Statement of some further Theorems on Lines of Force
139
SECTION PAGE 19 Potential of an Isolated Sphere
141
Capacity of an Isolated Sphere
142
Distribution from the Potential Point of View
143
Potential and Density distinguished
144
Important Case of a Spherical Condenser
145
The Plate Condenser
147
Formulæ for Capacities c
148
Energy of Charging and Discharging
150
Examples in Energy of Discharge
151
Energy of Discharge in the Cascade Arrangement of Leyden Jars
152
Electroscopes and Electrometers
153
Sir William Thomsons Quadrant Electrometer
155
Uses of the Quadrant Electrometer
158
Examples in Energy of Discharge c
159
General Consideration of Electrostatic Fields of Force
161
CHAPTER XI
163
Galvanis Experiment
164
Voltas Experiments and Views
165
Voltas Pile from Voltas point of View
167
Voltas Cell and the Couronne des Tasses from Voltas point of View
169
The Contact and Chemical Theories
170
Theory of the Simple Voltas Cell
171
Digression on the Galvanometer
173
Polarisation
175
Constant Batteries
176
Remarks on Cells and on Batteries
180
THE CHEMICAL PHENOMENA ACCOMPANYING THE PASSAGE OF THE CURRENT 1 Introductory
182
Chemical Effects General View
183
189
189
191
191
238
192
CHAPTER XIII
201
Statement of Ohms
203
Resistance further Discussed 4 The Exact Conditions on which Resistance Depends
204
Conductivity
206
Application of Ohnis Law in a Simple Case 7 Graphic Representation of Ohms
209
Applications of the Graphic Method 9 Divided Circuits
211
Slideform of Wheatstones Bridge
228
Wheatstones Bridge Resistance Box Form 7 Resistance of a Galvanometer
229
Resistance of a BatteryCell
230
Measurement of E M
231
Electrometer Methods Open Circuit
232
Voltmeter Galvanometers
233
Method of Opposition
234
246
246
249
249
CHAPTER XVI
252
The Simple ThermoCell
253
The ThermoPile
254
ThermoElectric Series
255
ThermoElectric Powers
260
The Neutral Point
261
ThermoDiagrams 8 Peltier Effect Observed Facts
263
The Thomson Effect
264
Theory of the Simple ThermoCell
265
Theory of the Peltier and Thomson Effects 252 253 254 254 256 257 259 263 264 265
268
CHAPTER XVII
271
The t and Directions of the Lines of Force 3 Simple Forn of Galvanometer 4 Relation of Strength of Field to CurrentStrength
275
SECTION PAGE 5 The Tangent Galvanometer
276
The Sine Galvanometer
279
The Multiplying Galvanometer
280
The Controlling Magnet Method
282
Sir W Thomsons Mirror Galvanometer
283
The Differential Galvanometer
285
The Ballistic Galvanometer
286
Sir W Thomsons Graded Potential Galvanometer
289
Sir W Thomsons Graded Current Galvanometers
290
Webers ElectroDynamometer
291
Some General Observations on Galvanometers
292
Galvanometers for Practical or Commercial use
293
ACTIONS BETWEEN CURRENTS AND MAGNETIC POLES MAG NETIC EQUIVALENT OF A CURRENT ACTION BETWEEN CURRENTS A...
294
The Absolute System of ElectroMagnetic Units
297
Summary of ElectroMagnetic Units see 3
298
The Dimensions of the Derived Units
299
Field due to a Circular Current
302
Magnetic Potentials due to Magnetic Shells
304
Magnetic Equivalent of an Electric Circuit
306
This Equivalence is for the External Field only
307
Reaction of a Pole on an Element of Current
308
Action of a Pole on an Incomplete Circuit
310
Action of the Earths Field on Currents Completely or Partly Mobile
311
Continuous Rotations of Currents
313
LAWS OF THE MOVEMENTS OF CURRENTS AS DEDUCED FROM THE CONSIDERATION OF MAGNETIC FIELDS AND POTENTIALS 1 M...
315
CHAPTER XX
324
Movements of Small Bodies in a NonUniform Magnetic Field
330
Is there Absolute Diamagnetism
336
CHAPTER XXI
342
General Expression for Induced E M
349
Constant Ioduced Currents
357
SECTION PAGE 9 Coefficient of Mutual Induction or of Mutual Potential
359
SelfInduction The Extra Current
360
Induced Currents of Higher Orders
362
CHAPTER XXII
363
Continuous Current Collected from Barlows Wheel
364
Induction in the Earths Field
366
Induction Coils General Plan
368
Practical Difficulties to be Overcome
369
Ruhmkorffs Coil
370
The Part Played by the Condenser
372
Condition of the Secondary Circuit when Closed
373
Secondary Circuit with AirBreak
374
Various Phenomena of the Secondary Discharge
376
High and Low Vacua
377
Discharge in High Vacua
379
CHAPTER XXIII
383
Clarks Machine
385
The Simple Commutator
386
Siemenss Armature
387
The Granıme Construction of Armature
388
The Gramme The E M F s Induced in the Ring
390
The Gramme The Collecting Brushes
392
The Lead that occurs when a Current is Running
393
Armatures Wound for E M F and for Current
394
The SiemensAlteneck Armature
395
SeparatelyExcited Machines
396
SeriesExcited Machines
397
ShuntDynamos
398
Other Methods of Winding
399
The Ferranti Alternate Current Machine
401
CHAPTER XXIV
402
SeriesDynamos as Motors
403
General Remarks on Dynamos and Motors
404
Formulæ for Activity c Maximum Activity
405
Efficiency
408
S P Thompsons Diagrams
409
Electric Railways and TramCars Telpherage c
411
Distribution of Potential in the Circuit of a Dynamo and Motor
412
CHAPTER XXV
416
Telegraphic Alphabets
419
The Needle System of Telegraphy
420
The Morse System
421
Relays
422
Earth Currents Condenser System of Working
424
Insulation of Wires
426
Telephones Introductory
428
The Bell Telephone
429
Telephones with External Source of Current
431
Properties of Selenium The Photophone
432
General Account of Electric Lighting
433
Work and Energy
450
230
xlv
271
xlvi
234
xlviii
275 275
xlix

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Página xxiii - A mass of 2^ kilogrammes loses, each 2\ minutes, a velocity of 300 metres per 2 hours. Express in dynes the force acting. 4. Two forces, of 30 dynes and 40 dynes respectively, act on a material particle at right angles to one another. Find the magnitude of their resultant, and the angle that it makes with the direction of the smaller force. 5. A force of 5000 dynes is resolved into others acting at right angles to one another. One of these is 3000 dynes. Find the other component, and the angle that...
Página 26 - If they are identical in mass and in dimensions, we have simply that m' - O § 4. Laws of Magnetism. — There are two fundamental laws in magnetism. I. Like poles repel, unlike poles attract, one another. This simple observed fact needs no comment. II. The force between two poles varies inversely as the square of the distance between them. It may also be stated that the force between two poles ^ and // is proportional to the product px p'.
Página 217 - Kirchhoff has enunciated in the form of two ' Laws ' the principles that must guide us in such an investigation. Law I. — If any number of conductors meet at a point, and if all currents flowing to the point be considered +, and ail currents flowing from the point be considered — , and if the condition of things be steady, or the potential at the point be not altering, then the algebraic sum of the currents meeting at the point must be zero. Or 2 . C = o.
Página 179 - DanielFs cell. — In this the only essential difference from the above is that we have copper in a saturated solution of copper sulphate, instead of platinum (or carbon) in nitric acid. But it is usually constructed having the zinc and acid in the porous pot, while very often the copper itself forms the outside vessel. The zinc may be surrounded by a semi-saturated solution of zinc sulphate, or of common salt, instead of by dilute sulphuric acid. Here the hydrogen reduces the copper sulphate ; sulphuric...
Página 30 - ... the vertical plane, that passes through the geographical north and south points, is called the plane of the geographical meridian. The earth's field can be resolved into a vertical and a horizontal component in this plane, as we shall see further in § 13. It is the horizontal component that acts on the ordinary compass, so that the magnetic axis of the needle will come to rest in this line. Hence, the plane of the magnetic meridian can also be defined as that vertical plane that contains the...
Página 127 - In the CGS system the unit of work is called, the ' erg,' and is the work done when a force of one dyne is overcome through a distance of one centimetre along the lines of force.
Página xxxviii - ... are connected with a galvanometer and the coil can be made to rotate about one of its diameters. On turning the coil half round, the galvanometer needle is momentarily deflected, but on causing it to rotate in one direction continuously and rapidly no effect is produced. Explain these two results. 4. A plane rectangular iron frame is placed vertically so that it faces due magnetic north.

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