Cathode Ray Tube Lecture Notes

Discovery of Cathode Rays

• William Crookes discovered cathode rays while studying electrical discharge in gases.
• J.J. Thomson furthered the study by identifying cathode rays as negatively charged particles called electrons.

Production of Cathode Rays

• Cathode rays are produced in a discharge tube, also known as the cathode ray tube (CRT).
• Structure of CRT:
  • Partially evacuated glass tube.
  • Cathode and anode positioned at each end.
  • A vacuum pump is used to evacuate the tube.
  • The cathode is connected to a power source via a clip, and the tube is supported on a stand.

Conditions for Cathode Ray Production

• Electric discharge occurs when:
  • The pressure inside the tube is low.
  • The potential difference between electrodes is high (10 kV - 20 kV).
• Pressure needs to be reduced to 0.0001 mm of mercury using a vacuum pump.
• A glow appears on the glass walls of the tube, indicating the presence of cathode rays.

Properties of Cathode Rays

• Travel in Straight Lines:

  • When an opaque object is placed in the path, a shadow is cast on the opposite wall.

• Charge:

  • Consist of negatively charged particles.
  • Deflect towards the positive plate when exposed to an electric field.

• Deflection in Magnetic Field:

  • When exposed to a magnetic field, cathode rays follow a curved path, confirming they are deflected by the field.

• Production of X-rays:

  • When cathode rays hit a metal with high atomic weight, they produce X-rays.

• Speed and Kinetic Energy:

  • Travel at high speed, nearly equal to the speed of light.
  • Possess kinetic energy, demonstrated by a paddle wheel that rotates when cathode rays strike it.