Experiment 8: A Relay Oscillator
64 Chapter 2
BAckground
Michael Faraday and capacitors
The earliest capacitors consisted of two metal plates with a very small gap
between them. The principle of the thing was simple:- If one plate was connected to a positive source, the positive charges at-
tracted negative charges onto the other plate. - If one plate was connected to a negative source, the negative charges
attracted positive charges onto the other plate.
Figures 2-67 and 2-68, shown previously, convey the basic idea.
The electrical storage capacity of a capacitor is known as its capacitance, and is
measured in farads, named after Michael Faraday (Figure 2-71), another of the
pantheon of electrical pioneers. He was an English chemist and physicist who
lived from 1791 to 1867.
Although Faraday was relatively uneducated and had little knowledge of math-
ematics, he had an opportunity to read a wide variety of books while working
for seven years as a bookbinder’s apprentice, and thus was able to educate
himself. Also, he lived at a time when relatively simple experiments could reveal
fundamental properties of electricity. Thus he made major discoveries including
electromagnetic induction, which led to the development of electric motors. He
also discovered that magnetism could affect rays of light.
His work earned him numerous honors, and his picture was printed on English
20-pound bank notes from 1991 through 2001.
Figure 2-71. Michael Faraday