PHYSIK UND CHEMIE
Ferdinand Braun Leipzig 1897 band 60.
Translation of the original German text
Over a procedure for the demonstration and for the study of the course of variable currents;
1. The next method describes the use of deflection of cathode rays by magnetic forces.
from Ferdinand Braun.
The rays are produced in tubes, from which one I indicate the measures, since these seems to me to be the generally most favorable (fig. 1).
K-is the aluminum cathode, A-anode, C-an aluminum diaphragm: opening of the hole = 2 mm. D a mica screen covered with phosphor. The glass wall E must be so evenly as possible and without knots, the phosphoresce screen must be made that way that one can see the fluorescent spot produced by the cathode rays through mica plate and the glass wall. For some attempts it is appropriate to place the mica screen under 45° to the tube axis. It is advisable, to use stanniol around the neck at the proximity of the diaphragm, which is led to the earth (even better would be to connect the diaphragm directly).
Mr. Franz Müller (Dr. Geissler's successor) in Bonn had the friendliness in a well-known excellent way to manufacture the tubes, which can be obtained by him.
The cathode rays are produced usually with a 20 plate Töpler's electrostatic generator; for many attempts also a rapidly working induction coil is sufficient. A variable spark gap switched into the circuit permits the most favorable kind of discharge.
I will describe some attempts.
Waveforms of currents.
The Curves are drawn after the appearance in the rotating Koenig's mirror.
Fig. 2a shows the waveform of the alternating current of the Strassburger power generator (50 whole oscillations per second). The current was led after reducing to an half Ampère (by means of a lamp connected into the circuit) by a coil of 50 mm length, 22 mm outside diameter, 10 mm internal diameter with an iron core. The coil lies horizontal; the coil axis, perpendicularly to the tube axis, and cuts the diaphragm. Amplitude of the curve 2-4 cm; as desired also more.
The waveform is surprisingly sinusoidal; fig. 2b. is an increased curve written by a tuning fork. It is continued as a dotted line still in fig.2a.
Fig. 3. and 4. refers to a small induction coil likewise placed with platinum circuit breaker (length of the coil 75 mm). Fig. 3a. the mode of motion of the primary circuit (secondary circuit open).
The ascending edge α β is so rapidly put back off that it is with difficulty recognizable because of the small luminous intensity.
γ β is the part of the starting current, while there is still a closed circuit.
The horizontal brightest line obviously corresponds to the lack of current.
Fig 3b. shows the waveform if the secondary circuit is electrical closed, which works at the same time on the cathode ray. The amplitude becomes about 2 1/2 times smaller, the waveform is more sinusoidal.
Fig. 3 C describes the electrical procedure, if the secondary circuit is closed by a Paraffin paper capacitor (like the one in bigger induction coils). I did not measure its capacity. It is like the fact that while the loading with (120 volt) alternating current from the mains power, a lamp heats up from dark red.
The figures show the relative storage of the waveforms.
This can be explained: With an unconnected secondary circuit, the iron core of the induction coil becomes again non-magnetic after each interruption; closing the secondary electric circuit means that the iron core remains continuously magnetic; switching the capacitor to the circuit, establishes that the core is demagnetized by the unloading current.
The alternating current goes through one vertically over the diaphragm placed coil; underneath the tube a small magnet staff (100 mm long, 14 min 6 mm thick) is rotating and shifted in a horizontal plane. With increasing rotation speed the bright spot describes the most diverse Lissajous waveforms; but only some are sufficiently calm, in order to appear satisfied. I could not bring the rotation speed of the magnet on unisono with my device.
4. Explanation of phase of the current against the electromotoric force due to induction and capacity.
The alternating current of the mains power goes through 1-6 parallel switched lamps, in order to be able to vary its strength between 0,5 and 8 Amp. It flows furthermore through an indicator coil which will swing the cathode ray in horizontal direction (direction I in fig. 5) and finally through the primary coil of the mentioned small Ruhmkorff, whose circuit breaker is closed. The secondary circuit of the apparatus supplies a thin coil (70 mm long, 30 mm thick) with inserted iron wire bundle, which serves as the second indicator coil and which will oscillate the spot in vertical direction (this can be seen in fig. 6d); it goes then to a change over switch, which permits either the coil of a Helmholtz carriage apparatus or a large induction free resistor. (the test conditions would be better selected if the two indicator coils are equal and if two secondary coils are equally phased ).
Fig 5a. shows the phase shift of the secondary circuit against the primary alternating current. Except the inevitable two coils an induction free resistor of 353 Ohm is switched on.
Fig. 5b gives the phase change, if the induction free resistor is replaced by a inductive resistor with the same Ohm resistance.
The constants are the same:
Ohm resistance = 353 Ohm.
Self induction coefficient = 0,83. 10² cm
frequency current = 50 sec―Ή
therefore the induction = 258 Ohm
and the apparent resistance (impedance) = 437 Ohm
If an iron wire bundle is slid into the inductive resistor, then the Curve 5c. develops; fig. 5 d, if the capacitor mentioned earlier is placed parallel to the inductive resistor; fig. 5e. if the coil is removed and only the capacitor is in the circuit.
It shows, except the phase shift in the overlay, about three times faster capacitor oscillations.
5. Phase shift by polarization.
The reduced to 0,5 Amp alternating current goes into two equal indicator coils from in sub 1 given dimensions. They are perpendicularly posed to each other. If one pushes the coils after switching on the same ballast resistors, into both branches in such a way that the Lissajous figure changes into a straight line under 45° inclination against the horizon.
Fig. 6 shows some results; fig. 6. a given movement of the point by the coil lain in the left or right side
Fig. 6b. shows: on the right a resistor of 2 Ohm; on the left a ZnSO4 resistor of 2 Ohm.
Fig. 6c. on the right a resistor of 2 Ohm, on the left the voltmeter.
Fig. 6d. in the left side an unipolar ZnSO4 resistance or the directly larger SH2O4-Volta meters with blank platinum plates can be switched on.
The ellipse itself looks more strongly elliptically by partly lifting of the electrodes by change of the Axis point.
If the voltmeter is replaced by a carbon resistor unit with Platinum electrodes and filled by diluted SH2O4, then the Curve changes again into a straight line, exactly as with the ZnSO4.
6. Finally I want to describe by attempts over the propagation rate of iron through magnetic excitation.
An iron staff of 1,2 m length and 9 mm in diameter lies horizontal and perpendicularly to the tube axis, its end as close to the diaphragm as possible. A small magnetizing coil which is movable is shifted onto the staff; a second one is arranged at a vertical level also perpendicular to the tube, so that under the simultaneous effect of an alternating current in both coils, a curve is described by the light spot, which substantially is present due to the pole close to the diaphragm. Both coils are supplied with the same alternating current.
If one shifts the coil on the long staff, then shape and orientation of the oscillating ellipse change, and if, the coil center is about 42 cm of the end of the staff, it shows a phase difference from π /2 (independently of the strength of the current); from the frequency (50) - the alternating current gives itself thereby a "reproduction speed" of the magnetic excitation of 86 (m/sec), a value, which agrees with the found conditions (88.7 in iron staff thick for 8,7 mm and the frequency 133) by Oberbeck.
It concerns by this procedure, as I admit, complicated features; - in that, a vast study will be necessary, in order to interpret the details of the observations.
The magnetic strength, which proceeds from the free end of the long staff, decreases with the increasing distance of the coil extraordinarily strong, much more than for a constant current.
This may be described by the following numbers:
Diversion by half diversion by
constant current alternating current
Coil at the end of the staff 32 mm 31 mm
Coil shifted over 10 cm 26 mm 23 mm
20 cm 16 mm 6 mm
30 cm 9 mm 4 mm
40 cm 6 mm 1 mm
7. An inertia of the cathode ray was not noticeable to me. Anyhow it follows the oscillations of the discharge of only one Leydener bottle. Even if is used without a spark gap by the secondary coil of a small (as indicator coil used) induction coil the light spot went upward, or downward 1 to 1.5 cm from the rest position.
The method of observation with the use of tubes up to now, use rather strong forces, but may be probably quite small in the future.
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