On J.J. Thompson Essay, Research Paper

J.J. Thomson

Science lectors who traveled from town to town in the in-between 19th century delighted audiences by demoing them the ascendant of the neon mark. They took a glass tubing with wires embedded in opposite terminals. . . set a high electromotive force across. . . pumped out most of the air. . . and the inside of the tubing would glow in lovely forms. In 1859 a German physicist sucked out still more air with an improved pump and proverb that where this visible radiation from the cathode reached the glass it produced a fluorescent freshness. Obviously the cathode emitted some sort of beam that was lighting the glass.

What could these beams be? One possibility was that they were moving ridges going in a conjectural unseeable fluid called the quintessence ( similar to the ether of Aristotle ) . At that clip, many physicists thought that this quintessence was needed to transport light moving ridges through seemingly empty infinite. Possibly cathode beams were similar to light moving ridges? Another possibility was that cathode beams were some sort of stuff atom. Yet many physicists, including J.J. Thomson, thought that all material atoms themselves might be some sort of construction built out of quintessence, so these positions were non so far apart.

Experiments were needed to decide the uncertainnesss. When physicists moved a magnet near the glass, they found they could force the beams about. Nevertheless, when the German physicist Heinrich Hertz passed the beams through an electric field created by metal home bases inside a cathode beam tubing, the beams were non deflected in the manner that would be expected of electrically charged atoms. Hertz and his pupil Philipp Lenard besides placed a thin metal foil in the way of the beams and saw that the glass still glowed, as though the beams slipped through the foil. Did that non turn out that cathode beams were some sort of moving ridges?

Other experiments cast uncertainty on the thought that these were ordinary atoms of affair, for illustration gas molecules as some suggested. In France, Jean Perrin had found that cathode beams carried a negative charge. In Germany, in January 1897 Emil Wiechert made a enigmatic measuring bespeaking that the ratio of their mass to their charge was over a 1000 times smaller than the ratio for the smallest charged atom. When Lenard passed cathode beams through a metal foil and measured how far they traveled through assorted gases, he concluded that if these were atoms, they had to be really little.

Pulling on work by his co-workers, J.J. Thomson refined some old experiments, designed some new 1s, carefully gathered informations, and so. . . made a bold bad spring. Cathode beams are non merely material atoms, he suggested, but in fact the edifice blocks of the atom: they are the long-sought basic unit of all affair in the existence.

One hundred old ages ago, amidst glowing glass tubings and the busyness of electricity, the British physicist J.J. Thomson was embarking into the inside of the atom. At the Cavendish Laboratory at Cambridge University, Thomson was experimenting with currents of electricity inside empty glass tubings. He was look intoing a long-standing mystifier known as & # 8220 ; cathode rays. & # 8221 ; His experiments prompted him to do a bold proposal: these cryptic beams are watercourses of atoms much smaller than atoms, they are in fact small letter pieces of atoms. He called these atoms atoms, and suggested that they might do up all of the affair in atoms. It was galvanizing to conceive of a atom shacking inside the atom & # 8212 ; most people thought that the atom was indivisible, the most cardinal unit of affair.

Thomson & # 8217 ; s guess was non unequivocally supported by his experiments. It took more experimental work by Thomson and others to screen out the confusion. The atom is now known to incorporate other atoms as good. Yet Thomson & # 8217 ; s bold suggestion that cathode beams were material components of atoms turned out to be right. The beams are made up of negatrons: really

little, negatively charged atoms that are so cardinal parts of every atom.

But, do atoms hold parts? J.J. Thomson suggested that they do. He advanced the thought that cathode beams are truly watercourses of really little pieces of atoms. Three experiments led him to this:

First, in a fluctuation of an 1895 experiment by Jean Perrin, Thomson built a cathode beam tubing stoping in a brace of metal cylinders with a slit in them. These cylinders were in bend connected to an electrometer, a device for catching and mensurating electrical charge. Perrin had found that cathode beams deposited an electric charge. Thomson wanted to see if, by flexing the beams with a magnet, he could divide the charge from the beams. He found that when the beams entered the slit in the cylinders, the electrometer measured a big sum of negative charge. The electrometer did non register much electric charge if the beams were bent so they would non come in the slit. As Thomson saw it, the negative charge and the cathode rays must someway be stuck together: you can non divide the charge from the beams.

All efforts had failed when physicists tried to flex cathode beams with an electric field. Now Thomson idea of a new attack. A charged atom will usually swerve as it moves through an electric field, but non if it is surrounded by a music director ( a sheath of Cu, for illustration ) . Thomson suspected that the hints of gas staying in the tubing were being turned into an electrical music director by the cathode rays themselves. To prove this thought, he took great strivings to pull out about all of the gas from a tubing, and found that now the cathode rays did flex in an electric field after all.

Thomson concluded from these two experiments that he could make nil but conclude that cathode beams were atoms of affair transporting a charge of negative electricity. The inquiry still remained, nevertheless: are they atoms, or molecules, or affair in a still finer province of subdivision?

Thomson & # 8217 ; s 3rd experiment sought to find the basic belongingss of the atoms. Although he could non mensurate straight the mass or the electric charge of such a atom, he could mensurate how much the beams were bent by a magnetic field, and how much energy they carried. From this information he could cipher the ratio of the mass of a atom to its electric charge. He collected informations utilizing a assortment of tubings and utilizing different gases.

The consequences were amazing. Just as Emil Wiechert had reported earlier that twelvemonth, the mass-to-charge ratio for cathode beams turned out to be over one 1000 times smaller than that of a charged H atom. Either the cathode rays carried an tremendous charge ( as compared with a charged atom ) , or else they were surprisingly light relative to their charge.

Philipp Lenard settled the pick between these possibilities. Experimenting on how cathode beams penetrate gases, he showed that if cathode beams were atoms they had to hold a really little mass & # 8212 ; far smaller than the mass of any atom. The cogent evidence was far from conclusive. But experiments by others in the following two old ages yielded an independent measuring of the value of the charge and confirmed this singular decision.

Thomson boldly announced his hypothesis that. He said that in the cathode beams, we have found a new province of affair, a province in which the subdivision of affair is carried beyond the ordinary gaseous province: a province in which all affair is of the same sort. This new signifier of affair being the substance from which all the chemical elements are built up.

Plants Cited

1 ) & # 8220 ; Thomson, Sir Joseph John. & # 8221 ; Microsoft Encarta 97 Encyclopedia. 1993-1996 Microsoft Corporation.

2 ) & # 8220 ; Thomson, Joseph ( 1856-1940 ) & # 8221 ; . Compton & # 8217 ; s Synergistic Encyclopedia. 1993, 1994 Compton & # 8217 ; s NewMedia, Inc.

3 ) Brazil, Georgia L, and Moore, Dan. & # 8220 ; History in Chemistry & # 8221 ; . Volume Library, Volume 1. Southwestern/ Great American Inc. , Nashville, Tennessee, 1998. p. 472-473.