Nikola Tesla Articles
Induction-Coil Potentials Page 568
Philosophical Magazine - April 1st, 1914
deflexion method. The value so found was 20·4 henries for a primary current of 5 amperes. By comparison with this, the same method being used, values of \(L_{21}\) were then obtained for other values of the primary current \(i_0\). The results are given in Table I.
Table I.
| \(i_0\), amperes. | \(L_{21}\), henries. | \(i_0\), amperes. | \(L_{21}\), henries. |
|---|---|---|---|
| 0·195 | 12·9 | 2·49 | 20·0 |
| 0·395 | 14·7 | 3·00 | 20·2 |
| 0·57 | 16·0 | 3·52 | 20·3 |
| 0·75 | 16·9 | 4·00 | 20·4 |
| 1·00 | 17·8 | 5·00 | 20·4 |
| 1·25 | 18·6 | 6·86 | 20·3 |
| 1·50 | 19·0 | 8·01 | 19·9 |
| 1·75 | 19·2 | 10·06 | 19·0 |
| 2·00 | 19·6 | 11·04 | 18·4 |
It will be seen from the table that \(L_{21}\) has its maximum value at 4 or 5 amperes, and that over the range 3 to 7 amperes it does not vary by more than 1 per cent. As most of the experiments described below were within this range, the value 20·4 was adopted for \(L_{21}\) in working out the theoretical expression (1) for the secondary potential.
The other method of determining \(L_{21}\) is to take the value of \(k^2\) measured with a condenser of considerable capacity in the secondary circuit, as described in the next section, in which case
\[ k^2 = \frac{M^2}{L_1 L_2} = \frac{L_{21}^2}{L_1 L_2}. \]
The values of \(L_1\), \(L_2\) being found from the periods of oscillation of the primary and secondary circuits when connected to condensers of known capacity, \(L_{21}\) can then be calculated from
\[ L_{21} = \sqrt{k^2 L_1 L_2}. \]
The values found were
\(k^2 = 0·839\), \(L_1 = 0·194\) henry, \(L_2 = 2540\) henries.
Hence
\(L_{21} = 20·3\) henries,
which is almost identical with the maximum value found by the other method. It may be concluded that up to the
