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chp3_chem - CATHODE RAYS and ELECTRONS Electrical Current...

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CATHODE RAYS and ELECTRONS Electrical Current - moving stream of electrons charge: S.I. unit is the Coulomb (C) current: S.I. unit is the Ampere (A) 1 A = 1 C/s
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Cathode Ray Tube (CRT) Tube with very little air inside Negative terminal ( Cathode ) Positive Terminal ( Anode ) Glass is lined inside with fluorescent mate- rial (glows when exposed to a current) Cathode Rays: Rays that were observed to stream from the cathode. in class demo
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J.J. Thomson’s Experiment: Charge to Mass Ratio of an Electron Used an Electric Field (oppositely charged fixed plates) and a magnet to show: Cathode Rays can be deflected both with E -Field and magnet. Cathode Rays are made up of negatively charged particles. The particles ( electrons ) have a charge to mass ratio: charge mass = e m e = 1 . 76 * 10 8 C/g
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Robert Millikan (1909): Oil Drop Experiment: Found the charge on an Electron Within a chamber of gas ionized by X-Rays Oil droplets fall between charged plates. Electrons from ionized gas stick to oil droplets. E -Field of plates directed upwards; opposite to gravity. Changing the charge on the plates changes droplets’ rate of fall. Allows us to find the charge on a droplet.
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Millikan found the charge on every droplet to be: a multiple of 1 . 60 * 10 - 19 C. So: The charge on an electron is: e = 1 . 60 * 10 - 19 C (negative). The mass of an electron: m e = 9 . 11 * 10 - 28 g.
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RADIOACTIVITY Henri Becquerel (1896) Left a piece Uranium on a photographic film. The Uranium left an image on the film. So the Uranium radiated something onto the film. Radioactivity is radiation coming from a piece of matter. The chemical properties of the matter changes. So: Does radioactivity involve a chemical re- action? No, it is more fundamental.
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RADIOACTIVITY (continued) Ernest Rutherford (early 1900’s): passed a beam from a radioactive sample between charged plates.
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