JJ Thomson
kamilanowak@yahoo.com
By: Anthony, Carly, Amanda,
Melissa, and Kamila
Background Info
• English physicist
• Born:1856
• Died:1940
• Attended Cambridge University, then
transferred to Owens College in 1870.
Became a lecturer after transferring to
third school, Trinity College.
Perceived structure
• JJ Thomson believed that atoms were
neutral and had no electric charge.
• He thought that electrons had a negative
charge.
• He thought that the atom is a spherical
object that has electrons inside a
homogeneous jellylike material.
Thompson’s perceived
structure of atom
Perceived Structure Cont.
• He thought that it had a massive positive
charge distribution cancels out the
electrons.
• Thomson's model is sometimes called a
plum pudding model.
Thomson’s
perceived structure
of atom.
Postulate of the theory
•
Thomson had theory that the ‘rays’ emitted from a electron gun were
inseparable from the latent charge.
•
Thomson had another theory that the rays carried a negative
charge.
Thomson's third theory was to try to work out the nature of the
particles. They were too small to have their mass or charge
calculated directly, but he attempted to conclude this from how much
the particles were bent by electrical currents, of varying strengths.
Experimental Design
• First Experiment:
• His first experiment was to build a cathode ray tube with
a metal cylinder on the end. This cylinder had two slits in
it, leading to electrometers, which could measure small
electric charges. He found that when applying a
magnetic field across the tube, there was no activity
made by the electrometers and so the charge had been
bent away by the magnet. This proved that the negative
charge and the ray were inseparable and intertwined.
First experiment
Cathode Ray
Experimental Design Cont.
• Experiment two:
• For this, he made a slightly different cathode ray tube, with a
fluorescent coating at one end and a near perfect vacuum. Halfway
down the tube were two electric plates, producing a positive and a
negative charge, which he hoped would deflect the rays.
• As he expected, the rays were deflected by the electric charge,
proving that the rays were made up of charged particles carrying a
negative charge.
Second
experiment
Cathode Ray
Experimental Design Cont.
• Experiment three:
• Thomson decided to try to work out the nature of the particles.
• He found out that the mass to charge ratio was so high that the
particles either carried a huge charge, or were extremely small. He
came up with the idea that the cathode rays were made of particles
that came from the atoms themselves.
Third experiment
Cathode Ray
http://www.experimentresources.com/cathode-ray.html
http://www.aip.org/history/electron/jjthoms
on.htm
http://nobelprize.org/nobel_prizes/physics/l
aureates/1906/thomson-bio.html