The conception of the field of force, or, as we should more correctly say, the field of energy, thus takes the place of the conception of action at a distance and of the ether. The beam of light and the electromagnetic wave (like that of the radio communication station or that surrounding a power transmission line) are therefore periodic alternations of the electromagnetic energy field in space, and the differ- ences are merely those due to the differences of frequency. Thus the electromagnetic field of the 60-cycle transmission line has a wave length of 3 X lO^V^O cm. = 5000 km. Its extent is limited to the space between the conductors and their immediate surroundings, being therefore extremely small compared with the wave length, and under these conditions the part of the electromagnetic energy which is radiated into space is extremely small. It is so small that it may be neglected and that it may be s…
Radiation, Light, And Illumination Passage Atlas
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Why This Theme Matters
Section titled “Why This Theme Matters”This passage may connect physical radiation, waves, visible light, measurement, and illumination practice.
Candidate Passages
Section titled “Candidate Passages”A simple harmonic oscillation as a line discharge would require a sinoidal distribution of potential on the transmission line at the instant of discharge, which is not probable, so that probably all lightning discharges of transmission lines or oscillations produced by sudden changes of circuit conditions are complex waves of many harmonics, which in their relative magnitude depend upon the initial charge and its distribution - that is, in the case of the lightning discharge, upon the atmospheric electrostatic field of force.
Consequently, in the polyphase motor running synchronously, that is, doing no work whatever, the secondary becomes current- less, and the primary current is the exciting current of the motor only. In the single-phase induction motor, even when running light, the secondary still carries the exciting current of the mag- netic flux in quadrature with the axis of the primary exciting coil. Since, this flux has essentially the same intensity as the flux in the direction of the axis of the primary exciting coil, the current in the armature of the single-phase induction motor run- ning light, and therefore also the primary current corresponding thereto, has the same m.m.f., that is, the same intensity, as the primary exciting current, and the total primary current of the single-phase induction motor running light is thus twice the exciting current, that is, it is the exciting current of the main magnetic flux p…
A simple harmonic oscillation as a line discharge would require a sinoidal distribution of potential on the trans- mission line at the instant of discharge, which is not proba- ble, so that probably all lightning discharges of transmission lines or oscillations produced by sudden changes of circuit conditions are complex waves of many harmonics, which in their relative magnitude depend upon the initial charge and its distribution - that is, in the case of the lightning dis- charge, upon the atmospheric electrostatic field of force.
between iron or magnetite terminals, and requiring about 75 volts, is white and very brilliant, that is, has a spectrum with many lines about uniformly distributed over the visible range. We can greatly increase the temperature of the arc by using a high-frequency condenser discharge: in this case very large currents of very short duration exist as oscillations between the terminals, with periods of rest between the oscillations, very long compared with the duration of the current. In this case the duration of the current is too short to feed a large volume of electrode vapor into the arc stream, and as the current is very large during the short moment of the discharge, the vapor between the terminals is very greatly overheated. Oscil- lating condenser discharges thus offer a means of increasing the temperature of the arc stream very greatly beyond the boiling point of the material. When using a condense…
If light is a wave motion, there must be something to move, and this hypothetical carrier of the light wave has been called the ether. Here our troubles begin. The phenomenon of polarization shows that light is a transverse wave; that is, the ether atoms move at right angles to the light beam, and not in its direction as. is the case with sound waves. In such transverse motion a vibrating ether atom neither approaches nor recedes from the next ether atom, and the only way in which in the propagation of the light wave the vibratory motion of each ether atom can be transmitted to the next one is by forces acting between the ether atoms so as to hold them together in their relative positions. Bodies in which the atoms are held together in their relative positions are solid bodies. That is, trans- verse waves can exist only in solid bodies. As the velocity of light is extremely high, the forces between the e…
circuit current during the fraction of the half-wave, which the discharge over the multi-gap arrester lasts, is moderate, due to its very short duration, and can easily be absorbed and radiated by the arrester; so that even if lightning discharges rapidly follow each other for some time, they can be taken care of by the arrester with moderate temperature rise : assuming a vicious thunder storm, in which lightning flashes succeed each other practically continuously, several per second. Each discharge causes a short circuit over the lightning arrester, varying in duration from nearly a half-wave - if the discharge occurs at the beginning of a half-wave - to practically nothing - if the discharge takes place near the end of a half-wave - ^that is, in average, for one-half of one-half wave, or :- • sec, in a 60 cycle system. Therefore from two to three lightning dis- charges per second would still short circ…
110. Artificial light is used for the purpose of seeing and distinguishing objects clearly and comfortably when the day- light fails. The problem of artificial lighting thus comprises con- sideration of the source of light or the illuminant; the flux of light issuing from it; the distribution of the light flux in space, that is, the light flux density in space and more particularly at the illuminated objects; the illumination, that is, the light flux density reflected from the illuminated objects, and the effect produced thereby on the human eye. In the latter, we have left the field of physics and entered the realm of physiology, which is not as amenable to exact experimental determination, and where our knowledge thus is far more limited than in physical science. This then constitutes one of the main difficulties of the art of illuminating engineering: that it embraces the field of two dif- ferent scie…
As the electromagnetic field represents energy storage in space, it cannot extend through space instantaneously, but must propagate through space at a finite velocity, the rate at which the power radiated by the source of the field can fill up the space with the field energy. The field energy is proportional to the energy radiation of the source of the field (transmission line, radio antenna, incandescent body) and to the electromagnetic constants of space (permeability, or specific inductance, and permittivity, or specific capac- ity), and the velocity of propagation of the electromagnetic field - that is, the velocity of light - ^thus is:
giving most of the light flux between the horizontal and 20 deg. below the horizontal; in many cases of indoor illumination a light source giving most of the light between the vertical and an angle of from 30 to 60 deg. from the vertical - depending on the diameter of the area of concentrated illumination and the height of the illuminant above it. It can also be done by modifying or directing the light flux of the illuminant by reflec- tion or diffraction and diffusion, either from walls and ceilings of the illuminated area, or by attachments to the illuminant, as reflectors, diffusing globes, diffracting shades, etc. Further- more, the required flux distribution can be secured by the use of a number of illuminants, and with a larger area this usually is necessary. Frequently the desired flux distribution is pro- duced by using an illuminant giving more light flux than neces- sary, and destroying the exc…
Hence the logical error which led to the ether theory is the assumption that a w^ave must necessarily be a wave motion. A wave may be a wave motion of matter, as the water wave and sound wave, or it may not be a wave motion. Electrical engineering has dealt with alternating- current and voltage waves, calculated their phenomena and applied them industrially, but has never considered that anything material moves in the alternating-current wave and has never felt the need of an ether as the hypothetical carrier of the electric wave. When Maxwell and Hertz proved the identity of the electromagnetic wave and the light wave, the natural conclusion was that light is an electromagnetic wave, that the ether was unnecessary also
67. In the theoretical investigation of electric circuits the velocity of propagation of the electric field through space is usually not considered, but the electric field assumed as instan- taneous throughout space; that is, the electromagnetic com- ponent of the field is considered as in phase with the current, the electrostatic component as in phase with the voltage. In reality, however, the electric field starts at the conductor and propa- gates from there through space with a finite though very high velocity, the velocity of light; that is, at any point in space the electric field at any moment corresponds not to the condi- tion of the electric energy flow at that moment but to that at a moment earlier by the time of propagation from the conductor to the point under consideration, or, in other words, the electric field lags the more, the greater the distance from the conductor.
To estimate the current which discharges in the lightning flash, the conductivity of air in the path of the discharge, and the diameter of the discharge are required, and as both are unknown, any estimate must be very approximate only. The specific resistance of gases and vapors decreases with increasing temperature and with decreasing pressure. It is a few ohm centimeters at atmospheric pressure and the high temperature of the magnetite or carbon arc, and is also a few ohm centimeters at the low temperature and low pressure of a high current Geissler tube discharge. The mercury arc stream also gives a specific resistance of a few ohms. The temperature of the air in the lightning discharge probably is moderately high, but the pressure is also not far from atmos- pheric, so that lOO ohm centimeters may not be very far from the true magnitude of the resistance. Estimating one to two feet as the diameter of…
44. Such circuits with distributed series capacity are of great interest in that it is probable that lightning flashes in the clouds are discharges in such circuits. From the distance traversed by lightning flashes in the clouds, their character, and the disruptive strength of air, it appears certain that no potential difference can exist in the clouds of such magnitude as to cause a disruptive discharge across a mile or more of space. It is probable that as the result of condensation of moisture, and the lack of uni- formity of such condensation, due to the gusty nature of air currents, a non-uniform distribution of potential is produced between the rain drops in the cloud; and when the potential gradient somewhere in space exceeds the disruptive value, an oscillatory discharge starts between the rain drops, and grad- ually, in a number of successive discharges, traverses the cloud and equalizes the pot…
istics of the illuminant, while flux density is a function of the space traversed by the light flux, but not of the source of light : with the same source of light, in the space from the surface of the illuminant to infinite distance, all light flux densities exist between the maximum at the surface of the illuminant (its brilliancy) and zero. Brilliancy thus is the maximum of the light-flux density. While intensity and brilliancy depend upon the shape of the illuminant, light flux is independent thereof. Illumination is a quantity which depends not only on the source of light, that is, light flux and flux density, but also on the illumi- nated objects and their nature, and thus is the light flux density as modified by the illuminated objects. Very commonly, how- ever, the term ” illumination ” is used to denote ” light flux density,” irrespective of the illuminated objects.
The unit of light intensity, or the candle power thus given, with a radiator of uniform light-flux distribution, 4 x lumens of light flux, and inversely, a radiator which gives 4 it lumens of light flux, gives an intensity of one candle, if the intensity is uniform in all directions, and, if the distribution of the intensity is not uniform, the average or mean spherical intensity of the radiator is one candle. Thus one mean spherical candle rep- resents 4 it lumens of light flux, and very frequently the mean spherical candle is used as representing the light flux: the light flux is 4 TT times the mean spherical intensity, and the mean spherical intensity is the total light flux divided by 4 it, regard- less whether the light flux is uniformly distributed or not.
81. If in a direct-current motor, at constant impressed voltage, the field excitation and therefore the field magnetism is decreased, the motor speed increases, as the armature has to revolve faster to consume the impressed e.m.f., and if the field excitation is increased, the motor slows down. A synchronous motor, however, cannot vary in speed, since it must keep in step with the impressed frequency, and if, therefore, at constant impressed voltage the field excitation is decreased below that which gives a field magnetism, that at the synchronous speed consumes the impressed voltage, the field magnetism still must remain the same, and the armature current thus changes in phase in such a manner as to magnetize the field and make up for the deficiency in the field excitation. That is, the armature current becomes lagging. Inversely, if the field excitation of the synchronous motor is increased, the magnet…
The phenomenon of interference proves that light is a wave, a periodic phenomenon, just like an alternating current. Thus the wave theory of light and radiation stands today as unshaken as ever. However, when this theory was established, the only waves with which people were familiar were the waves in water and the sound waves, and both are wave motions. As the only known waves were wave motions, it was natural that the light wave also was considered as a wave motion. This led to the question of what moves in the light wave, and thus to the hypothesis of the ether, with all its contradictory and illogical attri- butes. But there is no more reason to assume the light wave to be a wave motion than there is to assume the alternating-current wave to be a motion of matter. We know that nothing material is moving in the alternating- current or voltage wave, and if the wave theory of light had been propounded a…
Assuming a thunder cloud to pass over the line. The ground below the cloud then assumes an electrostatic charge, corresponding to the opposite charge of the cloud. The trans- mission line, as part of the ground, thus also assumes a static charge, higher than that of the ground, since it projects above it. Any equalization of the potential distribution in the cloud by a lightning flash, as discussed in the preceding, requires a change in the electrostatic charge of the line, corresponding to the changed potential difference between ground and cloud above the ground, and the static charge thus set free on the line rushes as an impulse or wave along the line. The wave shape of such impulses induced by cloud discharges is in general not a smooth sine wave, but may be very irregular : during the equalization of the cloud potential by the lightning flash, the potential difference against ground, of the part of…
The wave length of oscillation thus depends on the length of the circuit in which the stored energy readjusts itself. For instance, in the short circuit oscillation of the system, the wave extends over the entire circuit, including generators and trans- formers ; and the entire circuit so represents one wave, or one- half wave, that is, the wave length is very considerable. If the readjustment of stored energy takes place only over a section of the circuit, the wave length is shorter. For instance, if by a thunder cloud a static charge is induced on the trans- mission line, and by a lightning flash in the cloud, the cloud discharges, the electrostatic charge induced by it on the line
Naturally, as soon as determinations of spark voltages became available, attempts were made to estimate the voltage of a lightning flash. Considering, in a lightning flash, the dis- charge as that in an ununiform field, similar to that between needle points, and so requiring about 10,000 volts per inch. In this case, a lightning flash of two miles, or about 10,000 feet length, would require a potential difference of about 1200 million volts. The existence of such voltages in the clouds does not appear possible: a potential difference of 1000 mil- lion volts would produce a brush discharge of about one-half mile in length, before the final lightning flash occurs. In the brush discharge the air is electrically broken down, and becomes conducting. But it is also mechanically and chemically broken down, that is, the molecules are dissociated and recombine after the discharge, in all possible combinations. Th…
The shunt motor on an alternating-current circuit has the objection that in the armature winding the current should be power current, thus in phas£ with the e.m.f., while in the field winding the current is lagging nearly 90 deg., as magnetizing current. Thus field and armature would be out of phase with each other. To overcome this objection either there is inserted in series with the field circuit a condenser of such capacity as to bring the current back into p>hase with the voltage, or the field may be excited from a separate e.m.f. differing 90 deg. in phase from that supplied to the armature. The former arrange- ment has the disadvantage of requiring almost perfect con- stancy of frequency, and therefore is not practicable. In the latter arrangement the armature winding of the motor is fed by one, the field winding by the other phase of a quarter-phase sys- tem, and thus the current in the armature…
causes an oscillation in which the lower frequencies predominate, that is, a low-frequency high-power surge. A spark discharge from the line, a sudden high voltage charge entering the line locally, as directly by a lightning stroke, or indirectly by induc- tion during a lightning discharge elsewhere, gives a distribution of potential which momentarily is very non-uniform, changes very abruptly along the line, and thus gives rise mainly to very high harmonics, but as a rule does not contain to any appre- ciable extent the lower frequencies; that is, it causes a high- frequency oscillation, more or less local in extent, and while of high voltage, of rather limited power, and therefore less destruc- tive than a low-frequency surge.
Since the resultant m.m.f. of the machine, which produces the flux, is the difference of the field excitation, Fig. 21 D and the armature reaction, then if the armature reaction shows an initial os- cillation, in Fig. 21 E, the field-exciting current must give the same oscillation, since its m.m.f. minus the armature reaction gives the resultant field excitation corresponding to flux $>. The starting transient of the polyphase armature reaction thus appears in the field current, as shown in Fig. 22(7, as an oscillation of full machine frequency. As the mutual induction between armature and field circuit is not perfect, the transient pulsation of armature reaction appears with reduced amplitude in the field current, and this reduction is the greater, the poorer the mutual inductance, that is, the more distant the field winding is from the armature wind- ing. In Fig. 22(7 a damping of 20 per cent is assume…
Maxwell then has deduced mathematically, and Hertz demonstrated experimentally, that the alternating electro- magnetic field - that is, the electromagnetic wave - has the same speed of propagation as the light wave, and has shown that the electromagnetic wave and the (polarized) light wave are identical in all their properties. Hence light is an electromagnetic wave - that is, an alternating electro- magnetic field of extremely high frequency.
In a three-phase generator, if the e. m. f . of one phase con- tains a third harmonic, as is usually the case, then by connect- ing the three phases in delta connection, the third harmonics of the generator e. m. f.’s are short circuited and so produce a triple frequency current circulating in the generator delta. This triple frequency circulating current can be measured by connecting an ammeter in one corner of the generator delta, and the sum of voltages of the three third harmonics can be measured by putting a voltmeter in a corner of the generator delta. This local current in the generator winding is the triple frequency voltage divided by the generator impedance (the stationary impedance, at triple frequency, but not the syn- chronous impedance, since the latter includes armature reac- tion). In generators of low impedance or close regulation, as turbine alternators, this local current may be far mo…
To limit the machine current which followed the light- ning discharge, and so enable the lightning arrester to open the discharge circuit, series resistance was introduced in the arrester. Series resistance, however, also limited the discharge current, and with very heavy discharges, such lightning arresters with series resistance failed to protect the circuits, that is, failed to discharge the abnormal voltage without destructive pressure rise. This difficulty was solved by the introduction of shunted resistances, that is, resistances shunt- ing a part of the spark gaps. All the minor discharges then pass over the resistances and the unshunted spark gaps, the
[[PDF_PAGE:49]] Report of Charles P. Steinmetz 43 Denotations e = nominal induced E. M. F. of alternator or group of alternators. Xii = true self inductive reactance of alternator or group of alter- nators. xn= external reactance of alternator or group of alternators, thus. Xi = xn+Xi2 = total self inductive reactance of alternators or group of alternators. xj = effective reactance of armature reaction of alternator or group of alternators, thus: Xo=xn+x 2 synchronous reactance of alternator or group of alternators. x = reactance (or impedance) between alternators. z = impedance of circuit between alternators. = Vi- 2+(2x!+x) 2 , where r = resistance of circuit between alternators. Or approximately a = phase angle of circuit between alternators, where: tan a = Or approximately : a = 90 degrees. w = phase displacement from mean, of oscillating alternators, thus: 2co = total phase displacement of oscillati…
phase system, the three voltages, currents, etc., are displaced in phase from each other by 120°. Their third harmonics therefore are displaced in phase from each other by 3 X 120°, that is, by 360°, or in other words, are in phase with each other. In Fig. 169, such triple frequency fluxes in the three cores would have no magnetic return, except by leakage through the air, that is, cannot exist, except in negligible intensity, and there- fore the core type of three-phase transformer cannot give any serious triple frequency voltage. In the shell type Fig. 168, however, the three triple frequency fluxes, being in phase with each other, produce a triple frequency single-phase flux through a closed magnetic circuit. Where the circuit conditions and connections are such as to give a triple harmonic - as with YY connection - the shell-type three-phase transformer may produce triple frequency voltages, resultin…
The frequency of oscillations occurring in electric cir- cuits varies over an enormous range: from low frequencies, very little above alternator frequency, up to hundreds of mil- lions of cycles per second ; and the effect of the oscillations in the system therefore varies accordingly: from the relatively harmless static displays; brush discharges, streamers, sparks, etc., of extremely high frequencies, down to the disastrous high power low frequency short circuit oscillations, in which even in 10,000 volt system*^, currents ^i many thousands of amperes may surge, which voltages approaching 100,000, and with which no protective device can cope, which does not have unlimited discharge capacity, that is, contains no resistance whatever in the discharge path.
that is, the effective value of the discharge current is propor- tional to the condenser potential, e0, proportional to the square root of the capacity, C, and the frequency of charge, fv and inversely proportional to the square root of the resistance, r0, of the discharge circuit; but it does not depend upon the induc- tance L0 of the discharge circuit, and therefore does not depend on the frequency of the discharge oscillation. The power of the discharge is
80. As the result of the phenomena discussed in the preceding chapters, conductors intended to convey currents of very high frequency, as lightning discharges, high frequency oscillations of transmission lines, the currents used in wireless telegraphy, etc., cannot be calculated by the use of the constants derived at low frequency, but effective resistance and inductance, and therewith the power consumed by the conductor, and the voltage drop, may be of an entirely different magnitude from the values which would be found by using the usual values of resistance and induc- tance. In conductors such as are used in the connections and the discharge path of lightning arresters and surge protectors, the unequal current distribution in the conductor (Chapter VII) and the power and voltage consumed by electric radiation, due to the finite velocity of the electric field (Chapter VIII), require con- sideration.
by an opposite e. m. f. induced in this turn by its rotation through a quadrature field or commutating field, this field must therefore have the proper phase. The e. m. f. of alternation of the main field through the short circuited turn is proportional to the main field F and frequency N, and is in quadrature with the main field. The e. m. f. induced in the short circuited turn by its rotation (through the commutating field is proportional to the frequency of rotation or speed No, and to the commutating field Fo, and in phase therewith ; to be in opposition and equal to the e. m. f. of alternation, the commutating field must there- fore be in quadrature with the main field, and frequency times main field must equal speed times commutating field. That is :
The frequency at the wave length lWo is zero, since at this wave length the phenomenon ceases to be oscillatory ; that is, due to the energy losses in the circuit, by the effective resistance r and effective conductance g, the frequency / of the wave is reduced below the value corresponding to the wave length lw, the more, the greater the wave length, until at the wave length lWo the frequency becomes zero and the phenomenon thereby non-oscillatory. This means that with increasing wave length the velocity of propagation of the phenomenon decreases, and becomes zero at wave length lWo.
outer ones adjustable and set for about ^ in. gap. This lamp is connected across a high voltage 0.2-mf. mica condenser C, which is connected to the high voltage terminal of a small step-up trans- former T giving about 15,000 volts (200 watts, 110 •*- 13,200 volts). The low tension side of the transformer is connected to the 240-volt 60-cycle circuit through a rheostat R to limit the current. The transformer charges the condenser, and when the voltage of the condenser has risen sufficiently high it discharges through the spark gaps I by an oscillation of high frequency (about 500,000 cycles), then charges again from the transformer, discharges through the gap, etc. As several such condenser dis- charges occur during each half wave of alternating supply voltage the light given by the discharge appears continuous.
Since the resultant m.m.f. of the machine, which produces the flux, is the difference of the field excitation. Fig. 2 ID and the armature reaction, then if the armature reaction shows an initial os- cillation, in Fig. 21 E, the field-exciting current must give the same oscillation, since its m.m.f. minus the armature reaction gives the resultant field excitation corresponding to flux $. The starting transient of the polyphase armature reaction thus appears in the j&eld current, as shown in Fig. 22C, as an oscillation of full machine frequency. As the mutual induction between armature and field circuit is not perfect, the transient pulsation of armature reaction appears with reduced amplitude in the field current, and this reduction is the greater, the poorer the mutual inductance, that is, the more distant the field winding is from the armature wind- ing. In Fig. 22(7 a damping of 20 per cent is assumed,…