Nikola Tesla Books
Books written by or about Nikola Tesla
from this:
$! {l = {\sqrt{0.0684} \over 880} = {0.2615 \over 880} H} $! or $! {{261,500,000 \over 880} =} $! 297,160 cm.
Small correction should have been made for the e.m.f. making it smaller, this would have made the agreement with the calculated value close.
Coil wound with No. 2 wire
Readings were:
| e.m.f. | Current | ω | Resistance will be negligible | } |
|---|---|---|---|---|
| 6.6 | 49.1 | 880 | ||
| 6.6 | 49.1 | 880 | ||
| 6.6 | 49.1 | 880 |
| l1 $! {E \over Iω} $! = $! {6.6 \over {49.1 \times 880}} $! = |
| = $! {6.6 \over {491 \times 88}} $! H |
| or $! {{66 \times 10^{8}} \over {491 \times 88}} $! cm. |
| = 152,750 cm |
The dimensions are as follows:
diam. core 5" = 12.7 cm, length of core 38.25" = 97.185 cm. Turns 91. The diam. of wire insulation is $! {97.185 \over 91} $! = 1.068 cm. Diam. of bare wire 0.2576" = 0.6543 cm. This gives for 2 thicknesses 1.068 - 0.6543 = 0.4137 cm.
From this:
d = 13.1137 cm.; l' = 97.185 cm; N = 91; N2 = 8281;
S = $! {\pi \over 4} $!d2 = 145.0644 sq. cm. l1 = $! {4 \pi \over l'} $! N2S = 155,330 cm.
Probably resistance is not quite negligible, but results are close enough for ordinary use of coil.
Colorado Springs
Nov. 10, 1899
Measurements of the effective capacity of a vertical wire as modified by elevation, by resonance analysis and improved method of locating the maximum rise of e.m.f. on the excited system.
In the previous experiments on the same subject the maximum was located by observing a spark, but it was found that this mode of reading has a number of defects. One of these is the necessity of using spark wires, another the impossibility of locating the maximum very closely - except in cases when the tuning is very sharp. But when consi-
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18
Tesla: “High frequency oscillators for electro-therapeutic and other purpose”, a lecture delivered before the American Electro-Therapeutic Association, Buffalo, Sept. 13, 1898 L-156.
November 9
He performs the interesting measurements of the mutual inductance on the basis of the primary inductance when the secondary is open, and in short circuit. He measured inductances at constant current and frequency so the calculation procedure is simplified. The obtained mutual inductance he compared with the inductance determined previously by means of induced voltage under no load conditions. Tesla thinks that the difference originates from the influence of the secondary on the primary when the secondary is open. In some cases for the purpose of oscillator operating frequency reduction Tesla used two separate coils which he did not name but designated by numbers. He compared the calculated and measured values for these coils. The measured value on the basis of voltage the ratio method amounts to approximately 2% less than values measured on the basis of voltage, current and frequency. The calculated values are smaller in both cases. The correction of measured values according to comment of Oct. 26 is not large (approximately 5%) because the ratio D/1 is relatively small.
November 10
Had Tesla published the measuring methods he developed in New York and Colorado Springs, his name would probably be frequently encountered in earlier textbooks and handbooks on electrical measurements at high frequencies. As it is, we can only remark his exceptional ingenuity in designing measuring devices and the accuracy with which he determined the resonance of oscillatory circuits. An especially interesting feature is his method using a lamp already heated up by a supplementary power source, greatly increasing its sensitivity to small amplitude changes around the resonance peak of the oscillatory circuit.
November 10
He winds a new coil with 1314 turns on the same core on which he wound 689 turns (please see Oct. 18) and later 346 turns (please see Oct. 31). With this coil he measures the metal sphere capacitance again and achieves a similar value as on November 7, with "additional coil". At the end of these measurements and calculations he establishes that the method of resonance determination on the basis of spark length in the arc gap is not quite satisfactory. In the following experiments he changes the resonance determination procedure. He returns to a method which he applied earlier in the New York laboratory. That method was based on the use of an auxiliary secondary coil, in a weak inductive link with excitation system, at which terminal is the instrument for the registration of current or voltage change in the secondary. usually for the registration of changes a small bulb was used. The variation of the method is particularly interesting where the small bulb is preheated by means of a D.C. current (please see Fig. 2). The preheated bulb could register very small excitation changes from the high frequency direct current circuit, which are applied to additionally heat up the already preheated filament in order to emit visual light.
By using the newly applied method of resonance indication he performs some measurements again and he measures the capacitance of a vertical wire 50 ft. in length. After this he switches over to determine the coil self-capacitance with 1314 turns. The measured result he compared with the calculated one for the capacitance of a metal cylinder of the same shape as the coil. According to Tesla, this serves only as a rough estimate. When they are using the entire coil length in the first calculation, he obtained a higher value than measured, he takes the effective coil length on the basis of bare wire. It is obvious that Tesla looks for orientation of the theoretical equations in order to be able to estimate parameters, but the experiment is the most effective factor. As far as the problem of determining the coil self capacitance, this is evident from the first days of the notes (please see eg. June 20, July 3, etc.)
