Why and how are capacitors designed?

[cryingvalor]

Hey guys Im currently self studying electronics i have a background about it but its inadequate. Back in the school days they teach us mathematical computations and circuits about capacitors but i didn't appreciate it because it lacks something and that something is what i want now to know. Personally in order to understand something you have to start from the beginning and and get use to the words "why" "how" "what" "how come" , so here it goes.

For every inventions it was built for a purpose. It was built to solve a problem and in the case of the capacitor why was it built, what is its purpose, what lead scientist before to develop the capacitor and why is it design the way it is?

Hope you can help me guys, thank you

 

[nee.sarathi]

Re: Why Capacitor

Since electricity from frictional sources was usually weak, electricians of the eighteenth century searched for ways to increase charge and to accumulate as much of it as possible on a substance. If charge could be accumulated the electricians could then broaden their research with the mystical phenomenon.

The discovery of a device that was able to conserve quantities of charge for later use occurred in November 1745 and January 1746. Independently, two men discovered that electricity produced by an electrical friction machine could be accumulated and stored. Both men were horrified and surprised when their newly created device discharged into their bodies.

In November 1745, Ewald von Kleist, a German clergyman and scientist, and in January 1746 Petrus van Musschenbroek, a Dutch professor, discovered the magical condenser. This condenser or capacitor as it is now called was first named after professor Musschenbroek's hometown and university (Leiden or Leyden, Netherlands) by Abbe Nolett, a French scientist, who coined the term Leyden jar. The jar was once called the Kleistian jar, after von kleist, but this term was not lasting. (1) The first condenser was a jar or apothecary's phial containing a fluid with a nail piercing a cork stopper or bung, and connected to an electrical friction machine by a metal chain.

Ewald Jurgens (George) von Kleist (born in Prussian Pomerania 1700, died in Koslin, now Koszaln, Poland, on 11 December 1748) (2) was the son of a Prussian district magistrate. (3/176) He studied at the University of Leyden in the 1720's. While a student there he may have encountered the demonstrations in experimental physics of Professor 'sGravesande who was involved in electricity at Leyden. He apparently acquired his interest in science while at the University of Leyden. (3/176) Kleist returned to Pomerania to become dean or bishop of a cathedral chapter of Camin in Pomerania (NE Germany) at the time of his discovery. Von Kleist was a member of Prussian administrative squirearchy, (2) (or gentry) but was said to be seeking the ignition of spirits by sparks when involved with electricity. (4)

Germans were interested in electricity, and the interest was spreading to Berlin in the 1740's. At this period of time men interested in science were full of excitement stirred up by GM Bose, then a professor of the University of Leipzig, Germany. Individuals engaged with the phenomenon of electricity were igniting combustibles by using sparks from electrical friction machines. Frederick the Great had just opened the Berlin Academy of Sciences in January 1744. The newly opened Academy was holding demonstrations and experiments in electricity. Demonstrators ignited alcohol, gun powder, and turpentine by electrical sparks, and people upon hearing about these events went to hear and see for themselves.

The Berlin Academy soon held essay contests and for its very first contest selected the subject "causes of electricity." Just prior to the contest Johann Winkler's book on electricity was published and became available to contestants. Winkler speculated that electricity was a fluid similar to fire while his contemporary scientist Jacob Waitz thought it a form of heat and light. The first essay contest was won by a mining engineer. (5/250-260) German electricians soon got into developing their own theories of electricity, it was fashionable. Theories were developed by mining engineers, professors of physics, professors of classics, and even small town mayors. (5/250-260) The science of electricity in Germany was in a state of conjecture and many individuals were involved (amateurs and professionals).

Von Kleist apparently was also stimulated by Bose, and so made his own electrical machine to play with like everyone else. He repeated the experiments of those he heard and learned about; eg, Bose, Krueger, and Winkler. His goal was to increase the strength and reliability of the electrical flare flaunted by Bose. Von Kleist had erred, however, by thinking that the flares or sparks were proportional to the mass of the materials being electrified (greater the spark or schlag would be with the larger prime conductors of electrical machines). So while experimenting with his electrical machine and trying to achieve his goal he apparently connected the machine's prime conductor to a metal wire at one end, and placed the other end into a jar filled with water. He had insulated the jar after reading Charles Dufay, a French scientist, and believed the addition to the jar would increase the spark. (5/250-260) He was amazed (shocked)! By holding the jar in one hand while charging the jar with an electrical machine he acted as ground which in turn allowed the nail in the jar to serve as a positive pole. (4)

He made his discovery in October, (6) and began writing letters about his discovery on 4 November 1745. He wrote to Dr Lieberkuhn a famous physician, physicist, and member of the Berlin Academy who later reported the event to the Berlin Academy. (7) His next letter went to Mr Paul Swiettiki of Denmark on 28 November, and then to Professor Johann Krueger of Halle in December. Other letters were sent to Winkler of Leipzig, and a professor at the Academy of Lignitz. Krueger published von Kleist's experiment in Geschichte der Erde, Halle, 1746. All of the recipients of these letters were said to have replied that they were unsuccessful in replicating the experiment, (7) or that his experiment was amazing. The letters contained an account of von Kleist's experiment in which he inserted an iron nail through the cork placed in the neck of a hand held glass jar.

The jar probably contained alcohol, mercury , or water. Von Kleist connected the nail to his electrical machine and then electrified it. Touching the nail with the other hand, he received a severe shock. He was surprised that shocks were obtained only when he held the jar with both hands (closed circuits were unknown at that time), but when touching only the nail placed in the charged jar nothing happened. He claimed that his arm and shoulder of the hand holding the nail were numbed by the shock, and stated that not even Professor Bose would have liked a second kiss from the jar. Touching the charged nail of the jar to another object produced a strong spark as the jar discharged the electricity that it had stored.. Von Kleist had written to five individuals, and when they received additional information from him about his experiment they failed again. (5/229-323)

Between his first terrifying experiment and the time that he wrote the letters von Kleist had also discovered that when he removed the electrified jar from the electrical machine the spark appeared and remained long enough to provide some observable light in the room. He stated that he walked around the room many times with the light. Speculation has him adding alcohol to the jar so that the spark lighted the fuel for his light. (5/229-323) He had produced the flare of Bose but in a different fashion and more convincing manner.

Mr Swietlicke shared his copy of von Kleist's letter with fellow countryman Daniel Gralath who also failed to successfully replicate the experiment. Requesting additional information Gralath was informed that a metal wire served better than a nail, and that a barometric tube was better than a medicine phial. On 5 March 1746, Gralath succeeded in replicating the experiment. By this time, however, news from Leyden about Professor Musschenbroek's experiment had reached scientists in several countries. (5/229-323)

Benjamin Franklin became interested in the operation and rationale of the Leyden jar after observing a demonstration of its ability to shock people. After obtaining a Leyden jar and studying it he was able to show that the electrical charge was stored in the glass rather than the water that others had conjectured. He also discovered that the jar's electrostatic performance resulted from the substance that insulated the conductor. Franklin attempted to demonstrate his ideas or rationale by experimenting, and he did just that with the Leyden jar. He coated or wrapped both the inside and outside of a glass jar with a lead foil. Next he electrified the jar with one of his electrostatic machines, and then he removed the electrified metal wrappings without touching each other and found that each wrapping or sheet had been charged. After Franklin's discovery the Leyden jar took on different forms and was called a condenser. (8) Although Franklin had uncovered the rationale for the Leyden jar, the characteristics of its discharge had to await the next century.

Condensers, now called capacitors, are derived from the Leyden jar, and are devices that contain two conductors separated by an insulator (dielectric). The devices store electricity, and are essential components of an electrical circuit for electrical and electronic instruments. The larger the area of the conductors and the smaller their separation the greater their capacitance. Capacitors are either variable or fixed (electrolytic and nonelectrolytic). The dielectric material blocks the flow of direct current, but its constant charging and discharging permits alternating current to pass freely. (8)

Like all good and serviceable devices the condenser was periodically improved. In the 1850's, mica a natural occurring mineral (hydrous discilicate aluminum) was crafted into sheets, and used as an insulator. The mica sheets are tough, often laminated, and sometimes transparent. Mica is also a natural dielectric. Although mica was used as early as 1850, the demands for insulators in World War I placed it into commercial production. Mica placed between two metal plates formed a very good condenser. Paper and ceramic insulators became useful in condensers. Air, electrolytes, and plastic film are used presently as dielectrics. (8)

The jar, at the time of its discovery and afterward, offered new avenues of study for scientists, and they responded accordingly. The Leyden jar was adopted by electrotherapists, and by 1752 there were almost as many publications (40) of its use in medicine as there were (55) for its use in others areas. Use of the Leyden jar in medicine continued to increase over the years so that in 1789 there were 70 applications in medicine ascribed in publications while only 30 publications addressed its physical aspects. (9)

Although its use for entertainment tarnished its creditability somewhat, scientists continued their investigations involving the Leyden jar. Scientists had to learn the concepts of charge, current (movement), potential difference (force moving charge), and capacitance before completely accepting it as a tool in research. In 1785, Charles Coulomb measured its force between charged bodies. (9)

The claim for creation of the Leyden jar is uncertain. Some writers give claim to von Kleist, (10-12) while some claim that van Musschenboek (3, 9, 13, 14) was the real inventor. Some authors have assigned the credit to both men.

 

[cryingvalor]

Re: Why Capacitor

Thank for the history. Now i have more questions

1. how do capacitors store charge?, what specific materials are used? during the early experiments and todays modern capacitors.

2. for the function of a capacitor pls correct me if im wrong this analogy is how i understand the function of a capacitor. Capacitor is like a repeater it strengthens the signal by acting like the source by absorbing enough volts from the real source to supply the components connected to it. is it?

 

[yalanand]

Re: Why Capacitor

Capacitors store charges in the electric field.

This of capacitor like water storage tank. Where water is charge. Big capacitor is like big tank which takes lot of time (RC constant) to charge and small cap like small tank which fills very fast.

 

[ubna]

Re: Why Capacitor

Parallel plate capacitors stores charge in the two metal plates thereby creating electric field between the plates which holds the charge in the capacitor...
Now a days eletrolytic capacitors are used...