SECTION 3. DISCOVERY OF THE ELECTRON
The first evidence for sub-atomic particles came from experiments with the conduction of electricity through gases in sealed glass tubes at low pressures. Those tubes are called cathode ray tubes.
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6. What was the outcome of Thomson's experiment with cathode rays?
Click on Thomson's Experiment on the left side of the page and follow directions on the animation by clicking your mouse.
7. Name the four parts of a cathode ray tube.
8. Draw a sketch of the plates that produce an electric field.
9. What happens to the cathode ray in the presence of an electric field?
10. Which way is the ray deflected?
11. What happens to the cathode ray in the presence of a magnetic field?
12. Which way is the ray deflected?
13. What happens to the cathode ray when both the electric field and the
magnetic field are present?
14. Explain why the cathode ray is deflected upward in the presence of an
electric field.
15. Describe the behavior of particles in the presence of a magnetic field?
16. How did Thomson solved the problem of deflections?
17. What were his conclusions?
18. What was he able to calculate?
19. What fact did he find even though he used different sources of cathode rays?
20. What was the mass to charge ratio?
21. What was the name given to the new particle?
SECTION 4. MILLIKAN'S OIL DROP EXPERIMENT
In 1909 Robert Millikan used the classic oil drop
experiment to determine the charge of the electron.
22. Using your own words describe the experiment
conducted by Millikan.
23. Draw a labeled sketch of the experiment.
24. Draw a neat labeled free body diagram of the
forces on the oil drop.
25. What is the accepted value for the fundamental unit of charge?
Millikan's Oil Drop Experiment Links:
SECTION 6. RUTHERFORD'S GOLD FOIL EXPERIMENT
26. Describe Thomson’s model of the atom.
A Little Nut tells the story of the discovery of the nucleus of the atom. Read the story and answer the questions.
27. When the atoms in a gas acquire a positive or negative electric charge, the gas is said to be ionized. Describe the experiment performed by Rutherford to investigate how uranium rays ionize gas.
28. What were Rutherford's conclusions?
Use the following gold foil scattering experiment links to answer the questions below.
29. What were the names of the scientists that collaborated with Rutherford in this
experiment?
30. Using your own words, describe the gold foil experiment.
31. What did Rutherford expect to see?
32. Why did the results surprise Rutherford?
33. The Japanese physicist Hantaro Nagaoka imagined the atom to be like the
planet Saturn. He thought it had a positively charged ball in the center, with
hundreds of electrons in orbit around it. How does Rutherford experiment
validate Nagaoka's model?
34. Describe the planetary model developed by Rutherford.
