Structure of Atom - Cathode Rays and Discovery of Electron

Vocabulary flashcards covering the historical progression, experimental setup, properties, and quantitative measures of cathode rays and the discovery of the electron.

Dalton's Atomic Theory

An early atomic model introduced in $1808$.

Michael Faraday (1830s - 1850s)

Scientist who established that electricity interacts with matter through electrolysis and pioneered the early study of electrical discharge within partially evacuated glass tubes.

Julius Plucker (1899)

Scientist who achieved the critical conditions of high voltage ($>10{,}000\,\text{V}$) and low pressure ($10^{-4}\,\text{atm}$) to generate electrical discharge, discovering invisible rays traveling from the negative electrode to the positive electrode, termed cathode rays.

J.J. Thomson (1897)

Scientist who systematically analyzed cathode rays in electric and magnetic fields, conclusively proving they consist of negatively charged subatomic particles and discovering the electron.

Discharge Tube

An apparatus containing a cathode (negative electrode) and an anode (positive electrode) connected to a vacuum pump and high voltage source, operated at low pressure ($10^{-4}\,\text{atm}$) and high voltage ($>10{,}000\,\text{V}$) to generate electrical discharge.

Cathode Rays

Invisible rays traveling from the negative electrode (cathode) to the positive electrode (anode) inside a discharge tube.

Zinc Sulfide (ZnS) Coating

A phosphorescent coating material that glows when hit by invisible cathode rays, allowing their behavior to be observed.

Perforated Anode

An anode with a pinhole that allows cathode rays to pass through and strike a phosphorescent $\text{ZnS}$ coating behind it.

Source of Cathode Ray Particles

The metal plates or gaseous atoms present within the discharge tube.

Straight-Line Movement of Cathode Rays

A property of cathode rays where they move from the cathode to the anode in straight lines, creating a shadow of an object placed in their path.

Mechanical and Heating Effects of Cathode Rays

Properties of cathode rays demonstrated when they rotate a mechanical paddle by transferring kinetic energy ($\text{KE}$) and produce heat.

Deflection of Cathode Rays

The property of cathode rays deviating towards the positive plate in the presence of electric and magnetic fields, proving they are negatively charged particles.

Penetration Power of Cathode Rays

The ability of cathode rays to penetrate through a thin layer of metal.

Charge-to-Mass Ratio ($e/m_e$)

A constant value calculated by J.J. Thomson equal to $1.76 \times 10^{11}\,\text{C/kg}$, which is independent of the electrode material or the gas used in the tube.

Thomson's Limitation

The limitation that J.J. Thomson could only calculate the charge-to-mass ratio ($e/m_e$) of cathode rays, but could not calculate the electron's charge ($e$) or mass ($m_e$) separately.