Discovery of Electrons and Protons

Discovery of Electrons and Protons

Cathode Ray Experiment – Discovery of Electron (J.J. Thomson, 1897)

J.J. Thomson conducted the Cathode Ray Tube Experiment to study the nature of electric discharge in gases.

Experiment Setup:

• A glass tube was partially evacuated and sealed.

• Electrodes (cathode and anode) were placed inside the tube.

• A high voltage was applied across the electrodes.

• A fluorescent screen was placed to detect the rays emitted from the cathode.

Observations:

• A beam of rays emerged from the cathode (negative electrode) and moved toward the anode (positive electrode).

• The rays were deflected by electric and magnetic fields, indicating they carried a negative charge.

• When an obstacle was placed in the path, a shadow was cast on the opposite side, proving that the rays traveled in straight lines.

Conclusion:

• The rays consisted of negatively charged particles, later named electrons.

• The charge-to-mass ratio (e/m ratio) of electrons was calculated.

Diagram: Cathode Ray Tube Experiment by J.J. Thomson
(A labeled diagram of the cathode ray experiment showing the cathode, anode, and deflection of electrons.)

---

Goldstein’s Experiment – Discovery of Proton (1886)

E. Goldstein performed the Anode Ray Experiment (also called Canal Ray Experiment) to investigate the presence of positively charged particles in an atom.

Experiment Setup:

• A discharge tube with a perforated cathode was used.

• A low-pressure gas was filled inside the tube.

• A high voltage was applied across the electrodes.

Observations:

• A new type of rays, called anode rays or canal rays, was observed traveling in the opposite direction of cathode rays.

• These rays were positively charged and moved toward the cathode.

• The mass of these particles was much greater than electrons and depended on the gas inside the tube.

Conclusion:

• The positive particles were named protons.

• The charge of a proton was equal and opposite to that of an electron.

Diagram: Anode Ray Experiment by Goldstein
(A labeled diagram of the anode ray experiment showing the perforated cathode and movement of canal rays.)