From Ideas to Implementation

Ask the student to consider a stone: How would they go about finding its inner structure?

Many students "do Democritus", they smash the stone into smaller and smaller bits. What next? Some suggest looking through a microscope. The more technically oriented students point out that light or even electron microscopes cannot distinguish atoms and molecules. We need to "look" in a different way.

To distinguish the structure of the atom, we need to "throw" subatomic particles at our "stone" (Rutherford used gold foil).

A paradox: we need to fire subatomic particles, we do not know existence of, to find the structure of a nucleus !!

Imagination, technology, teamwork and some sheer good luck come to rescue:

History lesson

Very old idea
450 BC Ancient Greece: Democritus/Leucippus

"Any substance could be subdivided until an indivisible atomos was reached"

The idea was not tested and was later forgotten:

350 BC Ancient Greece: Aristotle

"All matter was classified into combinations of 4 elements, earth, water, air and fire"


Start of scientific enquiry in 1600:

1600 Germany: Guericke invented vacuum pump: can study gases at low pressure

1660 Ireland: Boyle distinguished elements and compounds

1665 England: Newton formulated laws of motion

1771 France: Lavoisier formulated law of conservation of matter: compiled a list of 28 chemical elements.

1780 Italy: Galvani found electricity in living things (excised frog legs move, when touched by metal). Mysterious Life Force?

1800 Italy: Volta continued Galvani's experiments and invented the electrical battery

1803-29 Swede: Berzelius Law of electrochemical process, linking electric and chemical behaviour

1808 England: Dalton proposed atomic theory and measured chemical equivalent weights. (Law of multiple proportions. All matter is made of atoms)

1831 - 1845 England: Faraday Discovered laws of electromagnetism and proposed the concept of charge

1868 Russia: Mendeleev Set up the modern Periodic Table
Predicted discovery of future elements

1875 England: Crookes discovered cathode rays and their properties - basis for the discovery of electron

1895 Germany: Roentgen new form of radiation: x rays

1896 France: Becquerel discovered natural radiation from some elements

1897 England: Thomson discovered that electrons are constituents of all atoms

1898 France: Curies discovered two radioactive elements radium and polonium

1902 England: Rutherford found radioactivity leads to transmutation of elements and a particle is emitted

1911 England: Rutherford Scattered a particles from gold foil and deduced that there is a heavy nucleus with rest of the atom mainly empty space

1932 England: Chadwick Identified neutrons from nuclear interactions

1939 Germany: Hahn/Strassman Nuclear fission discovered

Beginning of the Nuclear Age !!


Some insights

1) Beginning of 20th century: seemingly unrelated fields and technologies came together:

vacuum pump, electricity and natural radioactive elements allowed sophisticated experiments probing nature of the atom

2) Now obvious that matter consists of building blocks very unlike the macroscopic product!
Small massive nucleus where huge forces balance:
electrostatic repulsion of positive particles (protons) packed into a very small space against very short range strong nuclear forces. The rest of the atom contains a lot of empty space, where electrons orbit.

3) Even if you have a correct idea about the world (remember Democritus?), it is of low value until level of technology allows for it to be tested experimentally!

On a more practical level:

How can we "throw" subatomic particles? Rutherford used a particles, which are ejected from the nucleus at high speed already.

However, we can control trajectories and speed of charged particles by electric field E and magnetic field B.

Some very useful technologies: ink-jet printing, photocopying, oscilloscopes, TV.

Specimen Exam 2001 Some Exam answers (requires adobe acrobat reader)

Some Educational Websites of Interest for seminconductors and superconductors
Home |Physics Main Page |Faculty of Science | UNSW Main Page]  
Site Comments: physicsweb@phys.unsw.edu.au
© School of Physics - UNSW 2006