The branch of physics that deals with the property,interaction and structure of elementary particles is known as particle physics. Elementary particles are the fundamental constituent of all the matter in this universe. These microscopic scale particles plays an important role in this universe. So, elementary particles are the building blocks of the universe.
Simply elementary particles are the indivisible particles which are not made up of other particles. There are more than 100 elementary particles discovered so far. Till the time of John Dalton, atoms were considered to be the fundamental particles. With the growth and development of scientific research, James Chadwick discovered neutron, JJ Thompson discovered the electron and later Rutherford discoverd the atomic nucleus and proved that atom is divisible to further sub atomic particles. The discovery of quantum nature of particle by Max Planck revolutionize the understanding of elementary particles in microscopic scale. The research in elementary particles grew up higher with the advancement of science and technology. So, we have more than 200 short lived elementary particles today. Still researchers are devoting their whole career for the discovery of more subatomic particles. Some of the important particles are as follows:
Electron: It is the first fundamental particle discovered by JJ Thompson. It has charge equals to -1.6 × 10^16C and mass of 9.1 × 10^-31Kg.
Proton: It was discovered by Rutherford. It hs charge 1.6 × 10-19 column and mass of 1.6 × 10-27Kg. Itis 1836 times heavier than electron.
Neutron: It was discovered by Chadwick. It has mass of 1.67 × 10-27Kg and has no charge.
Positron: It was discovered by Anderson. It’s mass and charge is equal to that of proton but it is positively charged. So, it is also called as anti electron.
Antiproton: The mass and charge of antiproton is same as that of proton but it is negatively charged. So, it is also called anti-proton.
Antineutron: It has mass equal to that of neutron. When neutron and antineutron spins in same direction, their magnetic moment will be in opposite direction.
Neutrino and Anti neutrino: Neutrino was discoverd by Pauli. They have rest mass and charge equal to zero but carry momentum and energy. Both of them are stable particles. The only difference between them is their spins is in opposite directions.
Photons: Photons are the packet of electromagnetic energy that travels with the speed of light. Rest mass of photon is zero.
Classification of Elementary Particles: Elementary particles are categorized on the basis of their nature and properties. They are classified on the basis of mass, charge, average lifetime, spin, interaction etc.
On the basis of mass, particles are divided into four types:
- Massless particles
- Light particles
- Intermediate particles
- Heavy particles
On the basis of charge, particles are divided into three types:
- Positive particles
- Negative particles
- Neutral particles
On the basis of spin, particles are divided into two types:
On the basis of Interaction, particles are divided into four types:
- Gravitational force
- Strong force
- Weak force
On the basis of life time, particles are divided into two types:
- Stable Particles
- Massless particles
The classification chart of elementary particles is given below: