Wednesday, October 6, 2010

Thomson's Cathode Ray Tube

The Cathode Ray Tube

The cathode ray, even though not invented by the physicist J. J. Thomson, was perfected by him.  He made a model almost identical to the one in the image above.  He did this by getting a glass tube and inserting wires into two of the sides of the tube.  Once attaching these wires to metal discs, and connecting them to a high voltage he pumped the air inside the glass tube to a very low pressure.

First Experiment
In Thomson's first experiment, he was determined to find out wether or not it was possible to separate the ray itself and the magnetic charge of the particles in the ray.  To do this, Thomson set up his cathode ray with electrometers on the other side of a metal cylinder, which he had cut a slit in.  When he applied a magnet to the ray the electrometers read nothing.  This showed the Thomson that the ray had moved with the magnet and was effected by its magnetic field.  He later concluded that this proved that the ray and its negative electronic charge in inseparable.

This effect would have looked similar to this:

Second Experiment
For his second experiment, Thomson set his cathode ray up in a similar way as before in his first experiment.  This time however he set out to prove that the cathode ray carried an electronic charge.  After improving his vacuum in the tube he set up two aluminum plates that, when connected to a battery, formed an electric field.  When he attached the plates to a battery, making the top negative and the bottom positive, the cathode ray bent downwards away from the negative side.  This effect was also reversed when the positive and negative sides were changed.  This experiment proved that the particles in the cathode ray were negatively charged

The results of this experiment would look like this:

Third Experiment
In his last experiment Thomson decided to try to find the nature of the particles in the cathode ray.  By using lots of different gasses inside the tube, different types of glass, and changing the strength of the electric charge he set out to find out more about the particles.  He discovered the charge to mass ratio of these particles was a thousand times lower than the hydrogen atom.

A summery of these experiments using the cathode ray would be similar to this:

The importance and significance of Thomson's work with the cathode ray was due to the fact that the particles that he had discovered were smaller than any element in the world.  At this period of time no other subatomic particle and been discovered so the news of Thomson's discoveries was shocking.  Also a popular scientist that had come before Thomson named Dalton had said in his atomic theory that there was no particle smaller than element.  Thomson's work proved him wrong.

Works Cited

  • Cathode Ray Tube . Youtube. N.p., n.d. Web. 6 Oct. 2010. <‌watch?v=7YHwMWcxeX8>.
  • Dchummer. Cathode Ray Tube . Youtube . N.p., n.d. Web. 6 Oct. 2010. <‌watch?v=O9Goyscbazk&feature=related>.
  • “Experiments with cathode rays  .” Wikipedia . N.p., n.d. Web. 6 Oct. 2010. <‌wiki/‌File:JJ_Thomson_exp2.png>.
  • “Famous Experiments: Cathode Rays.” Physics LAB . N.p., n.d. Web. 6 Oct. 2010. <‌Document.aspx?doctype=3&filename=Magnetism_CathodeRays.xml>.
  • “J. J. Thomson .” wikipedia . N.p., 6 Oct. 2010. Web. 6 Oct. 2010. <‌wiki/‌J._J._Thomson#Experiments_with_cathode_rays>.
  • “J. J. Thomson’s Cathode Ray Experiment .” Experiment-reasourses . N.p., n.d. Web. 6 Oct. 2010. <‌cathode-ray.html>.
  • “Thomson’s Experiment .” Think Quest . N.p., n.d. Web. 6 Oct. 2010. <‌19662/‌low/‌eng/‌exp-thomson.html>.
  • 3 experiments, 1 Big Idea . N.p., n.d. Web. 6 Oct. 2010. <‌history/‌electron/‌jj1897.htm>.
  • Wordle . N.p., n.d. Web. 6 Oct. 2010. <‌create >.