Showing posts with label Cathode Ray. Show all posts
Showing posts with label Cathode Ray. Show all posts

Monday, June 3

JJ Thomson Cathode Ray

Introduction to JJ Thomson cathode ray

JJ Thomson received the Nobel prize in 1906 for his revolutionary work on the discovery of electrons.

He discovered electrons from the minute observations while performing the cathode ray tube experiment.

He added a number of enhancements in the cathode ray tube experiment, the results of which proved that there did exist subatomic particles. Prior to the discovery of electrons by JJ Thomson, all scientists believed that atoms were the smallest units of matter and they were indivisible.I like to share this Examples of Momentum with you all through my article.

Description of JJ Thompson cathode ray tube experiment

The cathode ray tube experiment comprises of the following arrangement:-

A long glass tube called the cathode ray tube is taken and evacuated so that air pressure inside it falls to a very low value - around 10^-2 to 10^-6 Pascals.

A metal cathode and a metal anode are fixed inside the two ends of the cathode ray tube described above.

The metal anode is connected to the positive terminal of a battery and is thus also called as the positive electrode.

The metal cathode is connected to the negative terminal of the battery and is thus also called as the negative electrode.

When electric current passed through the circuit, fluorescent green rays called the cathode rays were emitted from cathode and traveled towards the anode.

Observations and conclusions of JJ Thomson from the cathode ray tube experiment

JJ Thomson observed the following points from the cathode ray tube experiment that led him to the discovery of electrons.

Observations and their corresponding conclusions

The cathode rays were attracted by the positively charged anode - thus, the cathode rays were negatively charged.

The cathode rays were deflected by electric and magnetic fields - this further proves that they were negatively charged.

The cathode rays cast shadow of an object kept in their path - this proves that they travel in straight lines.

The cathode rays cause a light paper wheel kept in their path to rotate about its axis - this proves that they are composed of particles of some kind, because only matter can cause matter to move.

These were the main observations made by JJ Thomson in his cathode ray tube experiment. Thus, he concluded that the cathode rays consisted of some negatively charged particles called electrons, and thus, an atom could not be indivisible. The discovery of electrons in the beginning of the 20th century marked the beginning of a century of further discoveries that would introduce new concepts in science.