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Fantods, whole no. 9, Winter 1945

Page 23

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EFTY-NINE page 23
"Then my mind goes soaring upward
Far above our dreary ken,
To a desert, dying planet,
And a dying race of men."
We think Fancyclopedist Speer should have given us more of the poem, particularly the anticlimactic stanza which immediately followed the above:
"Oh, my little Martian sweetheart
In your crimson world afar,
I will soon be up to greet you
In my little space-o-car."
Which we'll wholeheartedly commend to the Bay Area Group.
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beautifulthoughtsbeautifullyexpressedbeautifulthoughtsbeautifullyexpres
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"Oh, come now, Dr. Channing...."
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Those of you who read G. O. Smith's "Firing Line", in the December 1944 Astounding will recall how the physicist, Farrell, invented a liquid of fabulously high dielectric constant and used it to make a condenser of super capacitance. And how concerned his boss, Don Channing was over the fragility of the glassware containing the charged condenser plates and the dielectric liquid. If it should break, the dielectric would leak out and decrease the condenser's capacitance to a very low value, whereat the terrific charge which Farrell had packed on the plates would send the voltage across them sky-high and catastrophic results would ensue.
A few calculations, based on the numerical data Smith's characters let drop, confirm Dr. Channing's mental arithmetic. Farrell started with a condenser having a capacitance of 0.98 microfarad with air between the plates. By replacing the air with his dielectric liquid he increased the capacitance to 13 farads. Then he charged the condenser to a potential of 3,000 volts. Now for potential, V, in volts, and capacitance, C, in farads, the quantity of electricity, Q, in couombs, stored on the plates is given by Q=CV. Whence we find the super-condenser must have had a 39,000-coulomb charge. Let us say that the super-dielectric is removed (I use this word advisedly) from the condenser. This reduces the capacitance from 13 farads to 0.98 microfarad. Since the condenser plates remain insulated from each other and from the ground, too, presumably, the charge on all of them is still 39,000 coulombs. But, as our Q=CV formula shows, all these coulombs squeezed into a 0.98-mfd condenser create a potential difference of nearly 40 billion volts, the thought of which gives Channing the willies.
But let's look at the situation from the standpoint of the amounts of energy involved in carrying out these operations. We may calculate the energy, in joules, stored in the condenser, by the formula E=1/2QV. We may then, if we wish, express this energy in more familiar units such as foot-pounds or kilowatt-hours. In this manner we come up with the fact that 3,000 volts across a 13-farad condenser represents 16.3 KWH of stored energy. All right, but let the capacitance drop to 0.98 mfd, with the concomitant rise in voltage to 40,000,000,000. How much energy does that represent? It works out as 216 million KWH. Which means that

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