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:

Millikan's Experiment
Britannica Explanation
Britannica Animation
Physics of Millikan's Experiment
ATOMIC DISCOVERIES
PART I. THE ATOM
SECTION 1. THE GREEK CONCEPT OF 'ATOMOS'
SECTION 2. JOHN DALTON: THE FATHER OF THE
                     CHEMICAL ATOMIC THEORY

PART II. THE ELECTRON AND THE NUCLEUS
SECTION 3. DISCOVERY OF THE ELECTRON
SECTION 4. MILLIKAN'S OIL DROP EXPERIMENT
SECTION 5. RUTHERFORD'S GOLD FOIL EXPERIMENT

PART III. PHYSICS AND POETRY
SECTION 6. PHYSICS AND POETRY
SECTION 6. RUTHERFORD'S GOLD FOIL EXPERIMENT

Plum-Pudding Model
26. Describe Thomson’s model of the atom.

The Nucleus
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.
The development of the experiment
How the experiment works 1
How the experiment works 2
Experiment results
Planetary model

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.