Overview of Discharge Tube Experiment

The discharge tube experiment involves passing high voltage through a partially evacuated glass tube to produce glowing beams (cathode rays) originating from the cathode.

Apparatus & Setup

• Glass discharge tube with electrodes
• High‑voltage DC power supply
• Gas pressure control (vacuum pump)
• Fluorescent screen or magnetic deflection coils

Experimental Procedure

1. Evacuate the tube to low pressure (~10⁻⁴ torr).
2. Apply high voltage between anode and cathode.
3. Observe glow discharge and movement of cathode rays.
4. Deflect the beam using electric or magnetic fields.

Key Observations

• Glowing region near the anode and dark space near the cathode (Crookes dark space).
• Cathode rays travel in straight lines from the cathode.
• Deflection by magnetic and electric fields indicates charged nature.
• Fluorescence produced when rays strike glass or phosphor screens.

Conclusions

The experiment demonstrates that cathode rays are streams of negatively charged particles (electrons) with high penetration and deflection properties.

Characteristics of Cathode Rays

• Charge: Negatively charged (deflected toward positive plate).
• Mass: Have small mass (determined by charge‑to‑mass ratio).
• Velocity: Can reach up to 10⁷ m/s.
• Penetration: Capable of passing through thin metal foils.
• Fluorescence: Cause certain materials to glow upon impact.

Applications & Historical Significance

Discovery of cathode rays led to the identification of the electron by J.J. Thomson and paved the way for modern atomic physics, electron microscopy, and vacuum tube technology.