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J.J. Thomson's Cathode Ray Experiment

  • A cathode ray tube is a long, evacuated glass tube with a metal anode and cathode placed on either side with a gap between the two
  • The anode and cathode are connected to the positive and negative sides of a battery respectively
  • When the voltage of the current is increased, electrons from cathode are projected in a blue green colored cathode ray towards the anode meaning that the ray in negatively charged
  • (4)

Citiations

1. Picture of J.J. Thomson

Squires, G. L. "J. J. Thomson." http://www.phy.cam.ac.uk/. N.p., n.d. Web. 7

Oct. 2010. <http://www.phy.cam.ac.uk/history/electron/photos.php>.

2. Experimental Information

Shuttleworth, Martyn. "J. J. THOMSON’S CATHODE RAY EXPERIMENT."

www.experiment-resources.com. N.p., 2008. Web. 7 Oct. 2010.

<http://www.experiment-resources.com/cathode-ray.html>.

3. Experimental Diagram

"J.J. Thomson's Cathode Ray Tube ." www.chemteam.info. N.p., n.d. Web. 7 Oct. 2010. <http://www.chemteam.info/AtomicStructure/Disc-of-Electron-Images.html>.

4. Description of Cathode Ray Tube

"Diagram of Cathode Ray Tube." www.tutorvista.com. TutorVista.com, n.d. Web. 7 Oct. 2010. <http://www.tutorvista.com/physics/diagram-of-cathode-ray-tube>.

5. Video Describing Experiment

The Discovery of the Electron (2 of 15). www.youtube.com. SciTechUK, 1 Mar. 2008. Web. 7 Oct. 2010. <http://www.youtube.com/watch?v=IdTxGJjA4Jw>.

Thomson's First Experiment(2)

  • Thomson's first experiment was to build a cathode ray tube with a metal cylinder in it which had two slits that lead to electrometers that were able measure small electric charges.
  • When a magnet was applied across the tube, the electrometer showed no activity because the charge had been bent away by the magnet, proving that the ray was negatively charged

J.J. Thomson(1)

Thomson's Third Experiment(2)

  • Thomson wanted to learn the size of these particles, but they were too small to measure directly
  • Thomson measured how far the beam was bent by electrical currents of varying strengths
  • Thomson's results showed him that these particles were 1,000 times smaller than a hydrogen atom, the smallest known atom, thus leading to the discovery of the electron

Thomson's Second Experiment(2)

  • For his second experiment, Thomson constructed a slightly different cathode ray tube which he added a flourescent coating and an almost perfect vacuum
  • In the middle of the tube, Thomson placed a two plates, one positively charged and one negatively charged which deflected the ray, proving that the ray was made up of negatively charged particles

What is a cathode ray tube?(3)

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