The Discovery and Behavior of Electrons

Jul 31, 2024

Discovery of Electron

Tools Used in the Experiment

  1. Glass Tube:
    • Contains gas (e.g., hydrogen).
  2. Vacuum Pump:
    • Decreases gas pressure to 10^-3 mm of Hg.
  3. Metallic Plates:
    • Cathode: Negatively charged.
    • Anode: Positively charged.
  4. High Voltage Source:
    • Provides ~10,000 volts to ionize gas.
  5. Emitter:
    • Detects flow of current in the circuit.

Experiment Overview

  • Discharge Tube:
    • Contains hydrogen gas at low pressure.
    • High voltage applied leads to continuous deflection of emitter, indicating current flow.
    • Cathode and anode are not connected; however, current is detected.

Investigation into Current Flow

  1. First Hypothesis:
    • Assume something unknown moves from the anode to cathode.
  2. Second Hypothesis:
    • Assume something unknown moves from the cathode to anode.

Experiment Part 1

  • Create a small hole in the cathode.
  • Coat cathode with fluorescent/zinc sulfide.
  • Result: No glow detected on fluorescent screen.
    • Conclusion: No flow from anode to cathode.

Experiment Part 2

  • Create a small hole in the anode.
  • Coat anode with fluorescent/zinc sulfide.
  • Result: Glow on fluorescent screen detected.
    • Conclusion: Something is moving from cathode to anode.
    • This is termed cathode rays.

Behavior of Cathode Rays

  • Electric Field:
    • Cathode rays bend towards the positive plate, indicating they are negatively charged.
  • Magnetic Field:
    • Cathode rays also deflect in a magnetic field.
  • Movement:
    • Travel in straight lines in the absence of fields.

Key Conclusions

  • Cathode rays do not depend on the material composition of cathode or anode.
  • Cathode rays are streams of electrons.
  • Cathode rays are basic constituent particles of all materials.

Millikan Oil Drop Experiment

  • Charge of electron: 1.6 x 10^-19 coulombs.
  • Mass of electron: 9.1 x 10^-31 kg.

Summary

  1. Cathode rays originate from cathode and move towards anode.
  2. Not visible but can be detected via materials like fluorescent screens.
  3. Travel in straight lines without electric or magnetic fields.
  4. Behave like negatively charged particles in fields.
  5. Characteristics are independent of electrode material and gas type.
  6. Electrons are fundamental constituents of all materials.

Final Note

  • Credit for the discovery of the electron primarily goes to J.J. Thomson.