JOURNAL OF CHEMICAL EDUCATION
608
A 1OObCYCLE DISTRIBUTION SYSTEM
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ALEXANDER P. MARION Queens College, Flushing, New York
FORseveral years the following scheme has been used to distribute a 1000-cycle voltage throughout the elementary physical chemistry laboratory with negligible interaction and no observable distortion of the wave form. The wiring normally used to carry direct current to the laboratory tables is isolated from the generator by pulling fuses and the output of a 10-watt amplifier driven by a 1000-cycle oscillator is plugged into a d.-c. outlet a t one of the tables. The highest
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RI - 5 W ohm& Io'watts R* = R. = 7 5 . m ohms, 1 watt
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impedance of the output transformer is selected and loaded with an equivalent amount of resistance. In this installation, for example, the 500-ohm terminals of the output transformer are used and are shunted by a 500-ohm, 10-watt bleeder resistor. Under load about 30 volts are delivered to the line. Two 75,000-ohm resistors are mounted in series on a small hoard and can he connected to the 1000-cycle line by means of ordinary POSJ lampcord and a polarized plug. (Use of a polarized plug prevents accidental insertion into an a.-c. receptacle.) Fahnestock clips are mounted on the hoard at each end of one of the resistors and serve as the student's source of the 1000-cycle signal. Measurements of resistances ranging from GO to 30,000 ohms by the Wheatstone bridge method have heen satisfactorily performed by eight groupssimultaneously. Even should a short circuit develop across one station there is a change of approximately 0.5 per cent in the supply voltage and this ordinarily is not detectable.
