1. Discovery of Electrons-Cathode Rays (By J.J. Thomson)

Discovery of Cathode Rays

J.J. Thomson used a cathode ray tube (CRT) to study particles emitted from the cathode.

Cathode Ray Tube (CRT) Setup

Glass tube, electrodes (cathode and anode), vacuum.

Cathode Rays Behavior

Rays travel in straight lines, deflect in electric and magnetic fields, cause fluorescence.

Deflection of Cathode Rays

Deflect towards positive plate (electric field) and direction depends on magnetic field, showing negative charge.

Charge-to-Mass Ratio

Thomson calculated e/m ratio of cathode rays, showing particles lighter than atoms.

Discovery of Electrons

Cathode rays are negatively charged particles, named electrons.

Plum Pudding Model

Thomson’s model: Atoms are a positive “pudding” with electrons embedded like plums.

Impact of Discovery

Revealed atoms have subatomic particles; led to development of atomic models and quantum theory.

Thomson’s Contribution

Identified electrons, established they are fundamental subatomic particles, changing atomic theory.