J.J. Thomson

J.J. Thomson By Nobel foundation [Public domain], via Wikimedia Commons


You have been learning about the history of the atom, looking at its discovery and development from ancient to modern times. You should first review what you have learned in the first three lessons of this series and then move on to exploring the evolution of modern ideas on the inner workings of atoms and J.J. Thomson’s contributions.


Review the history of the development of atomic theory by going to the Atomic Structure Timeline. This resource should help reinforce what you have learned about the long and eventful history of atomic discovery.

Now learn about the discovery of the electron by reading these two resources:

Feel free to explore the other interesting sections, links, and pictures to enhance your learning. As you explore these resources, think about your answers to these questions, which you can record on the J.J. Thomson student sheet:

  • Who was J.J. Thomson, and what was the nature of his work?
  • What did his experiments with cathode rays cause him to conclude?
  • Briefly describe the experimentation process that led him to this conclusion.
  • How would you describe Thomson? In what sense does he represent the best of human scientific endeavor?
  • Now, years later, how have Thomson’s assertions turned out?
  • What kind of impact did these findings about the inner workings of atoms have on technology?
  • What, in your opinion, is extraordinary about Thomson’s work?

Read some more about Thomson’s research at Discovery, 1897. You should briefly review Background to Discovery and then watch the Reconstruction of Thomson’s Experiment video. Then answer these questions on your student sheet:

  • What do you see?
  • What is happening in the experiment?
  • What is remarkable about the experiment itself and what you just viewed?

Once you've answered the questions, you will now have a chance to view and experiment with an interactive, virtual cathode tube. Before you do this activity, though, you should first read the orientation on the e/m experiment at the Interactive Animation of the E/M Experiment page from Discovery, 1897 so you understand in better detail what the e/m ratio represents and how it came to determine that an electron’s mass is about 2000 times smaller than a simple hydrogen atom. Please note that the animation linked to from this page does not appear to work. 

Once you've read the background information,  you can go to an animation of Thomson's Experiment using a cathode tube to measure the e/m ratio. You can view and experiment with the interactive, virtual cathode tube. Have fun playing with this innovative graphic apparatus by changing the different variables and adjusting the direction of the beam by moving the magnetic and electric field sliders.

Now, listen to this archive recording of Thomson in which he speaks about the atom. Based on what you hear in this recording, answer these questions on your student sheet:

  • What is Thomson talking about?
  • What connection does Thomson make between the discovery of the electron and unemployment?
  • In your opinion, how has the work of Thomson advanced the study of atomic theory and the role of science in society?

Finally, you should read through the last three sections of the Discovery, 1897 site and be prepared to discuss in class:


This esheet is a part of the The History of the Atom 4: J.J. Thomson lesson.

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Esheet Details

Grades Project 2061 Benchmarks National Science Standards