SIR JOSEPH JOHN THOMSON

Sam Wilson

Background

Born December 18, 1856 in Cheetham Hill, England.

His parents were Joseph James Thomson and Emma Swindells

He had one brother Frederick Vernon Thomson

Education

Thomson’s early education was in small private schools.

His parents wanted him to become an apprentice engineer to Sharp-Stewart & Co. but, in 1870 at the age of 14 he was admitted to Owens College.

1876 J.J. moved to Trinity College and four years later obtained his BA in mathematics.

In 1883 he received a masters degree.

Professor Thompson

In 1884 at age 28, Thomson became Cavendish Professor of Physics at University of Cambridge.

Cambridge is where he taught Earnest Rutherford and did all of his research on electrons.

Discovery of the Electron

Although some scientists had said that atoms were made up of a more fundamental particle roughly the size of a hydrogen atom, in 1897 Thompson was the first to state that they were much smaller than that…about a thousand times smaller.

He biased this statement on the fact that the rays coming off of atoms, cathode rays, could travel much further than a hydrogen atom.

Discovery of the Electron

Cathode Ray experiments. By applying an electric field to these rays Thompson

found that he could bend the rays and they bent away from the negative so, they were in fact negatively charged.

Thomson could also measure the angle they were deflected and calculate the ratio of the electrical charge to the actual mass of the particles.

He also found that the mass of these particles was constant no matter what gas they came off of.

Discovery of the Electron

With the cathode ray experiments Thompson concluded that atoms were divisible in to a much smaller particle. He originally called these particles

corpuscles. With this knowledge of electrons, or

corpuscles as he still called them, he went on to develop a new model of the atom.

Plum Pudding Model

In 1904 Thomson proposed that an atom is made up of electrons surrounded by a ball of positive charge. This keeps the whole atom having a neutral charge. He named this the plum pudding model

because of its similarity to the raisin electrons surrounded by the positive breading.

Isotopes

In 1912 during Thomson's work with his assistant F.W. Aston on the composition of canal rays he channeled a stream of ionized neon through a magnetic and electric field and observed two patches of light on the photographic plate.

They concluded that since there were two different paths the atom took there must be two neon atom of differing mass present in their sample, two isotopes of neon.

Thomson’s Other Achievements

1905 Thomson discovered the natural radioactivity of potassium.

1906 Thomson demonstrated that hydrogen only has a single electron per atom.

Personal Life and Honors

Thomson married one of his students at Cambridge; Rose Elisabeth Paget. They had two children, a daughter, Joan Paget Thomson and a son, George Paget Thomson.

He was honored several times for his work in physics. 1906 Nobel Prize 1908 Knighted by King Edward VII Honorary Doctorate degrees from 21 Universities

including Philadelphia University. In 1918 Thomson left research and became Master of

Trinity College until shortly before his death on August 30, 1940.

Sources

http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html

http://www.biography.com/people/jj-thomson-40039

http://www.atomicarchive.com/Bios/Thomson.shtml