Presentation Transcript

1. The Leyden Jar The Leyden jar is a simple device that "stores" static electricity in large amounts. It was the original form of the capacitor. The Leyden jar was used to conduct many early experiments in electricity, and its discovery was of fundamental importance in the study of electricity. Previously, researchers had to resort to insulated conductors of large dimensions to store charge. The Leyden jar provided a much more compact alternative. Ben Franklin perform many electrical experiments using these devices.

2. The initial discovery of the Leyden jar is credited to German physicist and Lutheran cleric Ewald Georg von Kleist, who in 1745 found a method of storing large amounts of electric charge. He lined a glass jar with silver foil, and charged the foil with a friction machine. Kleist was convinced that a substantial charge could be collected when he received a significant shock from the device.

3. This Kleistian jar went on to be known as the Leyden jar because in 1745 or 1746, Pieter van Musschenbroek of the University of Leiden, independently made the same discovery. Musschenbroek made the storage jar known to the scientific world, hence the jar was named after Leiden, the home town of the university.

4. A typical design consists of a top electrode electrically connected by some means (usually a chain) to a metal foil coating part of the inner surface of a glass jar. A conducting foil is wrapped around the outside of the jar, matching the internal coated area. The jar is charged by an electrostatic generator, or other source of electric charge, connected to the inner electrode while the outer plate is grounded. The inner and outer surfaces of the jar store equal but opposite charges.

5. See http://www.magnet.fsu.edu/education/tutorials/museum/leydenjar.html for further discussion of the Leyden Jar.

6. Ben Franklin performed many static electricity experiments using Leyden jars, or electrical phials, as he called them. Chagrined a little that we have been hitherto able to produce nothing in this way of use to mankind; and the hot weather coming on, when the electrical experiments are not so agreeable, it is proposed to put an end to them for this season, somewhat humorously, in a party of pleasure on the banks of the Skuykill. Spirits, at the same time, are to be fired by a spark sent from side to side through the river, without any other conductor than the water; an experiment which we some time since performed to the amazement of many. A turkey is to be killed for our dinner by electrical shock, and roasted by the electrical jack, before a fire kindled by the electrified bottle; when the healths of all the famous electricians in England, Holland, France, and Germany are to be drank in electrified bumpers under the discharge of guns from the electrical battery. April 29, 1749 Ben Franklin – The Original Physics Party Animal!!!!

7. Before I leave this subject of lightning, I may mention some other similarities between the effects of that and those of electricity. Lightning has often been known to strike people blind. A pigeon that we struck dead to appearance by the electrical shock, recovering life, drooped about the yard several days, ate nothing, though crumbs were thrown to it, but declined and died. We did not think of its being deprived of sight, but afterwards a pullet, struck dead in like manner, being recovered by repeatedly blowing into its lungs, when set down on the floor ran headlong against the wall, and on examination appeared perfectly blind. Hence we concluded that the pigeon also had been absolutely blinded by the shock. The biggest animal we have yet killed, or tried to kill, with the electrical stroke was a well-grown pullet. Philadelphia, 29 July, 1750.

8. Philadelphia, 25 December, 1750. I have lately made an experiment in electricity that I desire never to repeat. Two nights ago, being about to kill a turkey by the shock from two large glass jars, containing as much electrical fire as forty common phials, I inadvertently took the whole through my own arms and body, by receiving the fire from the united top wires with one hand, while the other held a chain connected with the outsides of both jars. The company present (whose talking to me and to one another, I suppose, occasioned my inattention to what I was about) say that the flash was very great, and the crack as loud as a pistol; yet, my senses being instantly gone, I neither saw the one nor heard the other; nor did I feel the stroke on my hand, though afterwards found it raised a round swelling where the fire entered, as big as half a pistol-bullet, by which you may judge of the quickness of the electrical fire, which by this instance seems to be greater than that of sound, light, or animal sensation.

9. Turkey killed by Electricity–Effect of a Shock on the Operator in making the Experiment As Mr. Franklin, in a former letter …, mentioned his intending to try the power of a very strong electrical shock upon a turkey, that gentlemen accordingly has been so very obliging as to send an account of it, which is to the following purpose: He made first several experiments on fowls, and found that two large, thin glass jars gilt, holding each about six gallons, were sufficient, when fully charged, to kill common hens outright; but the turkeys, though thrown into violent convulsions, and then lying as dead for some minutes, would recover in less than a quarter of an hour. However, having added three other such to the former two, though not fully charged, he killed a turkey of about ten pounds weight, and believes that they would have killed a much larger. He conceited, as himself says, that the birds killed in this manner eat uncommonly tender….. From this experiment may be seen the danger, even under the greatest caution, to the operator, when making these experiments with large jars; for it is not to be doubted but several of these fully charged would as certainly, by increasing them in proportion to the size, kill a man, as they before did a turkey.

10. PHILADELPHIA, 19 October, 1752. Make a small cross of two light strips of cedar, … tie the corners of the handkerchief to the extremities of the cross, so you have the body of a kite; which, being properly accommodated with a tail, loop, and string, will rise in the air, …. To the top of the upright stick of the cross is to be fixed a very sharp-pointed wire, rising a foot or more above the wood. To the end of the twine, next the hand, is to be tied a silk ribbon, and where the silk and twine join, a key may be fastened. This kite is to be raised when a thunder-gust appears to be coming on, and the person who holds the string must stand within a door or window, or under some cover, so that the silk ribbon may not be wet; and care must be taken that the twine does not touch the frame of the door or window. As soon as any of the thunder-clouds come over the kite, the pointed wire will draw the electric fire from them, and the kite, with all the twine, will be electrified, and the loose filaments of the twine will stand out every way, and be attracted by an approaching finger. And when the rain has wetted the kite and twine, so that it can conduct the electric fire freely, you will find it stream out plentifully from the key on the approach of your knuckle. At this key the phial may be charged; and from electric fire thus obtained spirits may be kindled, and all the other electric experiments be performed which are usually done by the help of a rubbed glass globe or tube, and thereby the sameness of the electric matter with that of lightning completely demonstrated.