In these series of lessons we will discuss the major shift of the understanding of matter and the nature of the atom.
Starting with the work of JJ Thomson with the discovery of the electron, Rutherford who proposed a new model of the atom and to Chadwick, who completed the model of the atom,... or so they thought.
Starting with the work of JJ Thomson with the discovery of the electron, Rutherford who proposed a new model of the atom and to Chadwick, who completed the model of the atom,... or so they thought.
JJ Thomson
After the development of voltaic piles, or batteries, in the early part of the 19th century, scientists were interested in testing different substances to see if they would be able to conduct electricity.
The ability to test gases was limited, that is, until the development of vacuum tubes. Invented by Geissler in 1855, it allowed the ability to produce a sealed tube containing a low pressure gas. Then in 1859, Plücker was able to seal wire ends into the vacuum tubes. This allowed for a current to pass through it.
What scientists noted is that, for a certain partial pressure of gas, a glowing beam was produced, but what was it? Was it a form of EMR, as Maxwell had theorised, or a beam of charged particles?
Prior to 1897, the atom was seen as indivisible. In fact, the term ATOM means indivisible. Indeed in the seminal experimental work of JJ Thompson in 1897, using electromagnetic principles, JJ Thompson discovered the first subatomic particle which we now know as the electron. This experiment radically changed our understanding of matter and eventually lead to the development of quantum mechanics.
The ability to test gases was limited, that is, until the development of vacuum tubes. Invented by Geissler in 1855, it allowed the ability to produce a sealed tube containing a low pressure gas. Then in 1859, Plücker was able to seal wire ends into the vacuum tubes. This allowed for a current to pass through it.
What scientists noted is that, for a certain partial pressure of gas, a glowing beam was produced, but what was it? Was it a form of EMR, as Maxwell had theorised, or a beam of charged particles?
Prior to 1897, the atom was seen as indivisible. In fact, the term ATOM means indivisible. Indeed in the seminal experimental work of JJ Thompson in 1897, using electromagnetic principles, JJ Thompson discovered the first subatomic particle which we now know as the electron. This experiment radically changed our understanding of matter and eventually lead to the development of quantum mechanics.
Theory
Watch the video to find out why (you may need to review charge behaviour in electric fields and charge behaviour in magnetic fields)
Watch the video to find out why (you may need to review charge behaviour in electric fields and charge behaviour in magnetic fields)
Interactive
Learn more about JJ Thomson's set up. Follow the instructions
Learn more about JJ Thomson's set up. Follow the instructions
Problems to try
- A beam of electrons travels through a set of crossed electric and magnetic fields. What is the speed of the electrons if the magnetic field is 82 mT and the electric field is 5.8 x 104 NC-1? (415 NC-1)
Electrons, moving at 7.5 x 10^7 m/s, pass through crossed magnetic and electric fields undeflected. What is the size of the magnetic field if the electric field is 4.4 x 104 NC-1? (5.87 x 10-4 T)
(Also check out questions on charge behaviour in electric fields and charge behaviour in magnetic fields )
This demonstration of an aspect of the JJ Thomson experiment is done in conjunction with University of Sydney Kickstart program and Crooked Science
