Wednesday, September 20, 2006

Cathode Rays and the Electron

Lesson Title: Cathode Rays and the Electron

Learning Outcome:
At the end of the sessions, you must be able to:
1. Discuss what cathode ray and radioactivity reveal about the atom.

Learning Presentation:
An atom is so small and yet it still have sub particles, how can you discover something so small that it has never been seen????????????

How did his experiment lead him to discovery this unseen particles

What did he discovered? click here

If you want to use your check another reference and get to know this person and his discovery better, check out your textbook its on pages 59 and 60.

1. Much of our understanding of the structure of the atom came from the study of electric charges in rarified gases. William Crookes (1832-1919), an English chemist, using a special vacuum discharge tube later called Crookes’ tube, show that there was some kind of matter coming from the cathode (negative electrode).

2. These particles were called cathode rays because they originated from the cathode. Numerous experiments made by Julius Plucker, Johann Hittarf, William Crookes, and others showed that cathode rays exhibited the following properties:
a. Cathode rays are emitted from the cathode when electric current is passed through an evacuated tube containing a gas at very low pressure.
b. The rays travel in a straight line as indicated by the shadow cast by small objects placed along its path. Metal objects struck by the rays become red hot.
c. The cathode rays upon striking a zinc sulfide (fluorescent) screen, cause it to emit random flashes of light.
d. The cathode rays have a negative charge. This is shown by the fact that they are attracted toward positively charged metal plates held outside the tube.

3. Joseph John Thomson (1856-1940), an English physicist, after a series of investigations, established the particle nature of cathode rays.He determined the velocity these particles and the ratio of electric charge (e) to mass (m), e/m.

4. The value is about –1.759 x 108 coulombs/gram. He further concluded that cathode rays are negatively charged and are fundamental particles of matter. Later they were called electrons.

5. Thomson helped revolutionize the knowledge of atomic structure by his discovery of the electrons.

What is this sub particle?and what is its importance to our lives today? post your answer in my amazing forum by clicking here

To test if you have gained sufficient knowledge
test yourself click here a score of more than 70% is considered sufficient
good luck :)


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