Transcript E/M Derivation

The Discovery of
the Electron
A PRESENTATION BY BERNARD NUAR, JOSH BOLTON, AND JUSTYN DAY
Cathode Ray Tube
• Inventor: Karl Ferdinand Braun 1897
• Specialized vacuum tube
• The cathode ray produced a bright
green light
How does it work?
• What was the composition and
properties of this mysterious ray?
The Initial Question
• How did the cathode ray
interact with the solid cross?
• Did these cathode rays have
particle or wave like properties?
• Made his own specialized
Crookes tube
• Maltese Cross
What does this mean?
Sir William Crookes
(1832-1919)
Therefore, the cathode ray has
particle like behavior!
Magnetic fields
Julius Plücker
(1801-1868)
• Discovered
that cathode
ray was
affected by
magnetic
forces
Jean Baptiste Perrin
(1870-1942)
• Perrin is given credit for
having discovered that the
particles that made up the
cathode ray were negatively
charged
• The beam is deflected
towards the positive end of
the magnet
Heinrich Hertz

Found that the electron passed through
thin gold sheets and illuminated on the
other side

First to apply an electric field to
manipulate rays path

Failed to manipulate the rays with
electric fields.

Brought the gold sheet observation to
Thomson’s attention
J.J. Thomson

Regarded as father of the electron

Proved the electron is
manipulated by electric fields with
lower pressures, which Hertz failed
to do

How did he do this?

He replicated and confirmed the
results of previous experiments

Calculated the charge to mass
ratio of the electron
J.J. Thomson’s cathode
• With an electric field
• Without an electric field
E/M Derivation
Q=Ne
•
•
•
•
N: number of particles in a cross section of the beam
m: Mass of the particle
v: Velocity
W: kinetic energy of the particle
• H: Magnetic field
• ρ: Radius of curvature
• e: Charge of an electron
• I: Current
• Q: quantity of electricity carried by the particles
What were his findings?
e/m = 1.7 x 10^7
About 1/1700 the ratio of Hydrogen!
Thomson’s Theories
Three theories based on experimental
observation
• Cathode rays are charged particles,
“corpuscles”
• These corpuscles were constituent of
atoms
• These corpuscles are the only
constituents of atoms (was later
proven wrong)
The name corpuscles was later replaced
with the term electron
Impact of the Findings
• The cathode ray was composed of electrons with particle like properties
• The electron charge to mass ratio was smaller than the hydrogen atom
•
It had a negative charge
• There must be an opposite charge to maintain electrically neutral atom
• Made possible the Plum Pudding model of the atom
• It made possible new technologies and advancements in scientific fields
What this discovery gave us:
The electron is very important for
many things we all use:
Emergence of new sciences
made possible:
• Quantum Physics
• Large Particle Accelerators
• Modern Chemistry
Questions