Discovery of Sub-Atomic Particles and the Electron

To understand the structure of the atom, experiments involving electrical discharge through gases were conducted.
A fundamental rule regarding the behaviour of charged particles serves as the basis for these observations: "Like charges repel each other and unlike charges attract each other."

In 1830, Michael Faraday demonstrated that passing electricity through an electrolyte solution results in chemical reactions at the electrodes.
These reactions lead to the liberation and deposition of matter at the electrodes.
Faraday formulated specific laws based on these findings (typically studied in Class XII).
These results provided significant evidence for the particulate nature of electricity.

During the mid-1850s, various scientists, notably Faraday, began studying electrical discharge in partially evacuated tubes called cathode ray discharge tubes.
Apparatus Construction:
- The tube is made of glass.
- It contains two thin pieces of metal sealed inside, referred to as electrodes.
- The negative electrode is the cathode.
- The positive electrode is the anode.
Experimental Conditions:
- Electrical discharge through gases is only observable under conditions of very low pressure.
- High voltages must be applied across the electrodes.
- Vacuum pumps are used to evacuate the tubes to adjust the pressure of the different gases inside.
Observations and Stream of Particles:
- When a sufficiently high voltage is applied, a current starts flowing.
- This current consists of a stream of particles moving from the negative electrode (cathode) toward the positive electrode (anode).
- These streams were designated as cathode rays or cathode ray particles.

Verification Technique: To confirm the flow of current from the cathode to the anode, an experiment was designed where a hole was made in the anode.
Coating Material: The glass tube behind the anode was coated with a phosphorescent material, specifically zinc sulphide ( $ZnS$ ).
Visual Evidence: When cathode rays pass through the hole in the anode and strike the $ZnS$ coating, a bright spot develops on the coating.
Real-World Application: This principle is the same one used in television sets, where images are formed by rays striking fluorescent or phosphorescent coatings.

(i) Origin and Movement: The cathode rays originate at the cathode and travel toward the anode.
(ii) Visibility: The rays themselves are invisible to the naked eye.
(iii) Observation of Behaviour: Their presence and behavior can be observed through their interactions with specific materials (fluorescent or phosphorescent) which glow when struck by the rays.