Discovery of Electrons

The first subatomic particle discovered was Electron

In 1897, J.J Thomson discovered negatively charged particles while studying the properties of cathode rays

Initially he called these particles corpuscles, but later they were renamed as Electrons

Electrons were the first subatomic particles that were discovered in an atom

Let us see how these electrons were discovered

J.J. Thomson's cathode ray tube experiments led to a very important scientific discovery, the electron, in 1897

Before we see how J.J. Thomson used the cathode ray tube to discover the electron, we need to know what a cathode ray tube is

Let us see the structure and working of a cathode ray tube (CRT)

The CRT consists of several elements starting with a tube that is vacuum sealed, so that the cathode ray does not collide with air particles inside the tube

On one side of the tube consist of cathode while the other side an anode

Cathode is a negatively charged conductor, whereas, the anode is a positively charged conductor

Negative charge particles from the cathode get attracted towards the anode

A small hole in the anode allows the negative charge particles to pass through it, creating a beam of those particles

The opposite side of the CRT is a fluorescent screen that glows when struck by the negative particles

Like this Thomson was able to see where the particles are hitting the screen

Electrons are not known to exist that time. So, the beams of negatively charged particles were called as 'Cathode Rays', as these particles were being emitted from the cathode

Now let us see how Thomson identified the charge of these particles of cathode ray

J.J. Thomson at first discovered that the cathode ray got deflected in presence of electric or magnetic field

Then he used electric field to determine the charge carried by the cathode rays

He introduced one positively charged metal plate and one negative charge metal plate near the anode

Now, when the cathode ray passed the anode, it bent towards the positively charged plate

And moved away from the negatively charged plate.This showed that the charge carried by the cathode ray was negative

These negatively charged particles were named as Electrons, which comes from the Greek word "elektron" which means "amber"


In 1987, J.J. Thomson discovered electrons while studying the properties of cathode rays

In his experiment of cathode ray tube, he put two oppositely charged plates to create a region of electric field

When he made the cathode ray to pass through this regions, he found that the ray bends towards the positively charged plate

Hence he concluded that cathode ray consists of negatively charged particles

These particles were named as electrons

This led to the discovery of First subatomic particle - Electron

The End