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INTERNATIONAL PROJECTIONIST
VOLUME V
NUMBER 6
SEPTEMBER 1933
STRUCTURE AND FUNCTION OF ELECTRICAL CONDENSERS
Aaron Nadell
THE most important practical fact about the electrical condenser is best explained by making a misstatement. The misstatement is that alternating current flows through a condenser, although direct current does not. If a condenser and a lamp bulb are connected in series with each other and supplied from an A.C. line, the lamp will light. This would seem to indicate that the condenser provides a conducting path for the alternating current. Actually, what happens is more complex. But at this point it may be said that if the same experiment is repeated with D.C., the lamp will not light.
In effect, therefore, although not in fact, the condenser is the reverse of a rectifier. A rectifier permits only direct current to flow through it. The eftect of the action of the condenser is as if only alternating current passed through it.
The simplest possible condenser consists of two sheets of metal fastened to opposite sides of a plate of glass. The reader may, if he wishes to experi
ment, build himself a condenser of this kind. He will find that a small light bulb placed in series with it will glow or light when alternating current is applied. If he makes a second condenser just like the first, and wires the two in parallel, he will find the illumination of the bulb increased. In other words, the condenser "conducts" alternating current, but not too well; it acts, in an alternating circuit, like a resistor. When resistors are connected in parallel the effective resistance of the circuit is decreased.
Condenser, built of alternate plates
of glass and metal, connected in two
parallel sets
[7]
Conversely, if the additional condenser is wired in series with the first, the light will dim down or go out; the effective resistance of the circuit having been increased, exactly as if condensers were resistors.
But it is plain that the condenser in an alternating circuit does not actually conduct current. Electricity cannot flow through the glass separating the two plates. One of the differences between the action of a resistor and that of a condenser in an alternating line can be shown by connecting a condenser in series with a pair of headphones and listening to alternating current of different frequencies. The loud speaker current of a sound system will serve for this purpose. It will be found that the high frequencies pass through the condenser more easily than do the low ones. This is not true of an ordinary resistor. A resistor of the carbon type will pass all frequencies equally well; a wire-wound resistor will tend to favor the lows — not because of its resistance