The document discusses the discovery and early study of electrons. Cathode rays were first observed in vacuum tubes in the 1850s and were studied by scientists like Hittorf, Crookes, and Goldstein. J.J. Thomson identified cathode rays as particles called "electrons" in 1897 based on experiments showing their small size and high charge to mass ratio. Rutherford later disproved Thomson's "plum pudding" atomic model using alpha particle scattering experiments. This led to Bohr's model of electrons orbiting the nucleus. Discovery of X-rays by Röntgen using a Crookes tube further demonstrated applications of electron beams.

1. What is it and what’s it doing in my
pudding?

3. Excuse me… how can you
discover a particle so small that
nobody has ever seen one?
J.J. Thomson 1897

4. Glowing tubes full of gas
proliferated – and gained
scientific importance – in
1855, when glassblower
Heinrich Geissler developed
an improved vacuum pump.
It was one of Geissler's
tubes that Julius Plücker
used when he first
observed cathode rays in
1859.

5. Plucker's student,
Johann Wilhelm Hittorf,
put solid objects inside
the tube between the
cathode and the glow.
The objects cast
shadows. Hittorf
concluded that the
cathode was emitting
something that traveled
in straight lines, like
light rays.

6.  Invented by
William
Crookes 1875
 Maltese Cross
Tube (on left)

7.  German physicist
Eugen Goldstein
called them “cathode
rays”
 Since they… well…
were emitted from the
cathode
 Goldstein discovered
positive rays which
were emitted by the
anode (“Canal” rays)

8.  Using devices similar to Crookes’ tube, studied
cathode rays
 Identified cathode rays as “electrons”
 Term coined by G. Johnstone Stoney (1891)
 Determined with basic physics
 e/m = 1.8 x 10-8 C/g
 Either they’re really small or highly charged
 Problem solved w/ Millikan’s “oil-drop” exp. in
1908

9. J. J. Thomson in his office
at the Cavendish
Laboratory. A colleague of
Thomson's, Lord Rayleigh,
said that "J.J. had
something to say on nearly
any subject that might turn
up. He as a good
raconteur, but also a good
listener, and knew how to
draw out even shy
members of the
company.... J.J., while
talking, paced the room
vigorously in a manner
rather suggestive of a
caged lion."

11. …came to the Cavendish
Laboratory as a young man
from New Zealand, and was a
research student under
Thomson. Using a-rays
emitted by radioactive
elements to probe into atoms,
around 1913 he showed that
Thomson's “plum pudding”
model of the atom was
untenable.

12. Other names to remember: Hans Geiger, Ernest Marsden

14.  Using a Crookes tube,
accidentally
discovered x-rays
 Discovery ranks
among shortest
scientific “gestation”
periods
 1st Nobel Prize

15.  Electrons move in
definite orbits
around the nucleus

17. "Could anything at first sight
seem more impractical than a
body which is so small that its
mass is an insignificant fraction
of the mass of an atom of
hydrogen? --which itself is so
small that a crowd of these atoms
equal in number to the population
of the whole world would be too
small to have been detected by
any means then known to
science.’’
-J.J. THOMSON

18. GROUP LEADER-
AAKASH KUMAR
GROUP MEMBERS-
1)HIMANSHU GALLOT
2)PUSHKAR KUMAR
3)
4)
The Electron
What is it and what’s it doing in
my pudding?
Excuse me… how can you
discover a particle so small that
nobody has ever seen one?
J.J. Thomson 1897
Glowing tubes full of gas
proliferated – and gained
scientific importance – in
1855, when glassblower
Heinrich Geissler developed
an improved vacuum pump.
It was one of Geissler's
tubes that Julius Plücker
used when he first
observed cathode rays in
1859.
Plucker's student, Johann
Wilhelm Hittorf, put solid
objects inside the tube
between the cathode and
the glow. The objects cast
shadows. Hittorf concluded
that the cathode was
emitting something that
traveled in straight lines,
like light rays.
Crookes’ Tube
Invented by
William Crookes
1875
Maltese Cross
Tube (on left)
A later manifestation of
Crookes’ Tube German physicist
Eugen Goldstein
called them “cathode
rays”
 Since they… well…
were emitted from
the cathode
Goldstein discovered
positive rays which
were emitted by the
anode (“Canal” rays)
Using devices similar to Crookes’ tube,
studied cathode rays
Identified cathode rays as “electrons”
 Term coined by G. Johnstone Stoney (1891)
Determined with basic physics
 e/m = 1.8 x 10-8 C/g
 Either they’re really small or highly charged
 Problem solved w/ Millikan’s “oil-drop” exp. in
1908
J.J. Thomson
J. J. Thomson in his office at the
Cavendish Laboratory. A
colleague of Thomson's, Lord
Rayleigh, said that "J.J. had
something to say on nearly any
subject that might turn up. He
as a good raconteur, but also a
good listener, and knew how to
draw out even shy members of
the company.... J.J., while
talking, paced the room
vigorously in a manner rather
suggestive of a caged lion."
Plum-Pudding Model
…came to the Cavendish
Laboratory as a young man
from New Zealand, and was a
research student under
Thomson. Using a-rays
emitted by radioactive
elements to probe into atoms,
around 1913 he showed that
Thomson's “plum pudding”
model of the atom was
untenable.
Ernest Rutherford (1871-1937)
Gold-Foil Experiment
Other names to remember: Hans Geiger, Ernest Marsden
Modern View
of the Atom
So what do you do with a
newly characterized electron
beam?
Shoot it at things, of course
Introducing…
Wilhelm Röntgen (1895)
Using a Crookes tube,
accidentally discovered
x-rays
Discovery ranks among
shortest scientific
“gestation” periods
1st Nobel Prize
Early Models of the Atom
Bohr
Electrons move in
definite orbits
around the nucleus
Crooke’s-Hittorf X-ray Tube
"Could anything at first sight
seem more impractical than a
body which is so small that its
mass is an insignificant fraction
of the mass of an atom of
hydrogen? --which itself is so
small that a crowd of these atoms
equal in number to the population
of the whole world would be too
small to have been detected by
any means then known to
science.’’
-J.J. THOMSON