Electrons to Quarks

Subatomic Particles:

from Electrons to Quarks

Rakesh Mohan Hallen

Electrons

* Can an electron reverse its spin from +1/2 to -1/2 or vice versa?

* Why is a magnetic field created by the flow of electrons?

* How was an electron born? Why does it move around the nucleus?

* Is an electron divisible into other particles?

* From where do the electrons get the energy to revolve around the nucleus?

* How is it possible that though the drift velocity of the electron is 0.1cm/s to 1cm/s when the light is switched on the bulb starts glowing immediately.

* Is there any way to distinguish between two electrons not located in the same atom but having equal energy and parallel spin?

* Who was the first person to see the electron with his naked eyes?

'Electron' like 'atom' is a concept in science, which helps us to explain a vast array of natural phenomena. As was mentioned last month the concept of electron was conceived by Stoney and J. J. Thomson provided the experimental evidence for it.

The electron has a negative electric charge but it is not drawn into the positively charged nucleus. It is said to have spin, but one can never tell, which is the direction of this spin. It is responsible for the colour of all objects, but we do not know its colour. In the realm of atoms rules are not the same as in the world we are all familiar with in our daily life. No wonder a young student often feels like Alice in Wonderland. Understanding the atomic concepts requires abandoning many of our pet notions. Thus there is no possibility of seeing an electron with 'naked eyes'. Their existence can only be inferred from the analysis of various natural phenomena.

A set of rules regarding electrons is often necessary to explain several phenomena related to it. For example, according to the Pauli's exclusion principle, no two electrons in an atomic orbital can have exactly same set of quantum numbers. Often two electrons in an orbital differ only in their spin quantum number. However, in the realm of atoms we cannot say that this electron has spin +1/2 and that one has spin -1/2. All we can say is that the two electrons in a particular atomic orbital have opposite spins. Thus there is no restriction that an electron in an atomic orbital has to have the same spin (quantum number) always, the only restriction is that if it occupies an orbital in which there is another electron, its spin must be opposite to that of its companion. When an electron gets excited, that is gets promoted to a higher energy level, the same restriction applies. Thus an electron may indeed 'reverse' its 'spin' provided the configuration of electrons that results does not violate the Pauli's exclusion principle.

Several concepts in science are inter-related. The concepts: Magnetic field, electric current and electrons constitute a group of concepts in science, which are inter-related in a particular fashion. Maxwell's equation relating an electric current to a magnetic field is one such relation. Thus an electric current, which is due to the motion of electrons, leads to a magnetic field around the current carrying conductor. One may draw an analogy between this relation with the relation "gravitation is the cause of attraction between two bodies which leads to acceleration," between the concepts gravitation attraction and acceleration. Using such relations we can explain a wide variety of phenomena. For example, the relation between a electrons in motion with magnetic field helps us to explain why there is an electric current can be detected in a coil of copper wire when a magnet is brought close to it. As a scientist, we all learn to accept these relations are the basic axioms of science that cannot (or need not?) be explained.

When electric current in a circuit is switched on, electrons in the conducting wire near the switch accelerate. The electrons further down the metallic wire are affected, and therefore are also accelerated, because of the electrostatic repulsion that is propagated as an electric field or as an electromagnetic field. Thus the information that some electrons are accelerating at one end of an electric wire is transmitted to its farther end through the electromagnetic field/wave, which as we all know, travels as fast as light. This explains why although the drift velocity of electrons in a conductor is very low an electric current is transmitted much faster. In fact it is transmitted with a velocity that is almost equal to the velocity of light.

One can between two electrons having the same value of energy (including spin) as much as one can distinguish two exactly identical objects.

Protons, Neutrons, Neutrino and Quarks

* Are there any particles other than electrons, protons and neutrons in an atom?

* There are no electrons in the nucleus then how are the beta particles emitted in nuclear reactions?

* What are quarks, neutrinos and positrons?

* Is it possible to change neutrons to other fundamental particles of atom?

* What is the colour of the fundamental particles such as electrons, protons, neutrons etc.?

* How is it that some neutral particles called neutrons, together with some particles called protons, are held together in the nucleus? Since like charges repel each other why do the particles not fly apart?

* Why is the number of neutrons in an atom almost always more than the number of protons or electrons?

* Can an antiproton, antineutron and collectively form antimatter just as proton, neutron and electron form an atom?

* The neutrinos and antineutrinos are electrically neutral, when these are annihilated how is it presumed that only photons are produced, why not gravitons?

Yes, there are particles other than electrons, protons and neutrons in an atom. Quarks, neutrino or positron are the names of some of these particles. In fact, the number of particles known till today, that can be found in the universe is more than hundred. But many of these particles may not be present all the time in an atomic nucleus, they are produced when