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Updated: June 22, 2025
Next connect the other post of the variable condenser to the or negative electrode of the A battery; the + or positive electrode of this to one terminal of the detector filament and the other end of the latter to the electrode of the A battery.
In bulbs provided with a conducting terminal, though it be of aluminium, the brush has but an ephemeral existence, and cannot, unfortunately, be indefinitely preserved in its most sensitive state, even in a bulb devoid of any conducting electrode. In studying the phenomenon, by all means a bulb having no leading-in wire should be used.
This done, he unscrewed all the light bulbs from their sockets lest, when he turned the switch, a sudden glow through the shades arouse some prowling watchman's curiosity. Then he took up the other strand of his wire, to which was attached a carbon electrode, knelt on the floor and gingerly, for so much juice suggested many possibilities to a novice touched the carbon to the safe door.
This latter relay action will be explained when we come to its operation as an amplifier. We have just learned that when the stream of electrons flow from the hot wire to the cold positive plate in the tube they form a conducting path through which the battery current can flow. This is the reason the vacuum tube amplifies as well as detects. How the Three Electrode Tube Acts as a Detector.
In employing very high frequencies the loss of energy by the bombardment is greatly reduced, for, first, the potential needed to perform a given amount of work is much smaller; and, secondly, by producing a highly conducting photosphere around the electrode, the same result is obtained as though the electrode were much larger, which is equivalent to a smaller electric density.
With a diamond, carborundum or zirconia button the photosphere can be as much as one thousand times the volume of the button. Without much reflecting one would think that in pushing so far the incandescence of the electrode it would be instantly volatilized.
This is done merely to enable the apparatus to perform the work which it is not capable of performing at ordinary air pressure. In the bulb we are able to intensify the action to any degree so far that the brush emits a powerful light. The intensity of the light emitted depends principally on the frequency and potential of the impulses, and on the electric density of the surface of the electrode.
As already stated, the applied electrical potential determines whether or not deposition of a metal upon an electrode actually occurs. The current strength determines the rate of deposition and the physical characteristics of the deposit. The resistance of the solution is generally so small as to fall out of practical consideration.
In this instance, by touching the bulb with one or two fingers, one or two shadows of the stem inside were projected against the glass, the touch of the finger producing the same result as the application of an external negative electrode under ordinary circumstances. In all these experiments the action was intensified by augmenting the capacity at the end of the lead connected to the terminal.
This latter relay action will be explained when we come to its operation as an amplifier. We have just learned that when the stream of electrons flow from the hot wire to the cold positive plate in the tube they form a conducting path through which the battery current can flow. This is the reason the vacuum tube amplifies as well as detects. How the Three Electrode Tube Acts as a Detector.
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