A PRESENTATION BY BERNARD NUAR, JOSH BOLTON, AND JUSTYN DAY

The Discovery of the Electron

Cathode Ray Tube

• What was the composition and properties of this mysterious ray?

• Inventor: Karl Ferdinand Braun 1897

• Specialized vacuum tube

• The cathode ray produced a bright green light

How does it work?

The Initial Question

Sir William Crookes (1832-1919)

• Did these cathode rays have particle or wave like properties?

• Made his own specialized Crookes tube

• Maltese Cross

• How did the cathode ray interact with the solid cross?

What does this mean?

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

• Without an electric field

• With an electric field

E/M Derivation• 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

Q=Ne

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