From gutaye@ncat.edu Wed Apr 30 21:31:39 1997
Date: Wed, 30 Apr 1997 21:00:38 -0400 (EDT)
To: Every one
April 30, 1897 !!!
  • Homepage of the Electron: On April 30, 1897 the first subatomic particle called the electron by J.J. Thomson of Cambridge in England. I am just wondering what was happening in Ethiopia in 1897 ?. Well, I looked at Professor Bahiru Zewde's book (A history of Modern Ethiopia). We were just begining to recover from the battle of Adwa.

    What did J.J. Thomson discover ?

    Today, April 30 1997, marks the 100th aniversary of the discovery of electron by J.J. Thomson (1856-1940). Professor Thomson used a simple velocity selector device in combination with a cathode-ray tube. Subatomic paricles were accelerated from the cathode (-) to the Anode (+) with a known speed given by
    Here V is the potential difference and q is the charge of the particles that will soon be named electrons. He let the particles pass through the velocity selector in a straight line by fine tuning the applied magnetic and electric fields. Such balance would mean

    That is Electric force = qE = magnetic force = qvB. Here v is the selected speed. Now, it is easy to see that the selected speed is the same as the speed of the charged particles emanating from the cathode. You can easily see from the second equation that when you devide the electric field with the magnetic field (E/B), you will get v again. Now when you equate the two speeds. The result is interesting


    Squaring both sides and proper rearangement gives

    The ratio q/m is called charge to mass ratio. According to current experiments. This ratio is 1.75881962(53) X 10^11 C/kg. C stands for Coulomb which is a unit of charge, and killogram (kg) is the unit of mass. This is the core of the discovery. Professor Thomson and his colleagues used different materials for the cathode. It turns out that this ratio is independent of the the materials. This independence showed that the particles are common constituents of matter. 15 years after this discovery Professor Millikan, American Physicisist discovered the charge of the electrons from his oil-drop experiment. The charge of the electron is q = 1.60217733(49)x10^-19 C 

    Exercise: From the above results determine the mass of the electron in 
killograms, Negelect the correction factors in both e/m and e values

    The schematic diagram of the experiment is shown below

    Conclusions

    Thanks to the electron we have drinking water, soda, cafe-au-lait e.t.c Thanks to the electron we have medicine and my brain too. Thanks to the elctron we are here figthing over meatless bones. Thanks to the electron for the big screen TV, for my Beamer. Thanks to the electron, I can teach from the key board.

    Come to think of it, what was happening in Ethiopia in 1897. According to the history books we were just recovering from the battle of Adwa. My great grand parents, told their grad sons that they were tired of feeding Italian captives. Let's say that we were feeding Italian captives. If the Italians stayed in their own home, and the mesafint work out their differences, ethiopians would have discovered the electron and other things.

    Let's get busy to learn. For more details regaring the discovery of the Homepage of the Electron.

    Negati bula

    ak, the bihere chilalo awaraja,