THERMOELECTRIC GENERATOR

Introduction: 

A working of Thermoelectric Generator - (TEG) is based on the direct interconversion of heat and electricity, The Seebeck Effect produces an electric current when dissimilar metals are exposed to a variance in temperature. 

Principle:

when two materials are exposed to different temperatures there is a resultant voltage between the two. Thermoelectric generators take heat input at one end of the material and then induce a voltage due to the difference in temperatures between them. 

There have been different materials that are being used in the thermoelectric generators and a majority of them are now using semiconductors. Thermoelectric power generators have the same basic configuration, as shown in the figure.

WORKING MODULE:

 A circuit containing thermoelectric materials which generate electricity from heat directly. A thermoelectric module consists of two dissimilar thermoelectric materials joined at their ends: an n-type (with negative charge carriers), and a p-type (with positive charge carriers) semiconductor. Direct electric current will flow in the circuit when there is a temperature difference between the ends of the materials.

Atom bomb

Atom Bomb

The  principle of fission is made use of in the construction of the atom bomb. As atom bomb consists essentially of two pieces of ₉₂U²³⁵ (or ₉₂Pu²³⁹) each smaller than the critical size and a source of neutrons. The subcritical masses of U²³⁵ in the form of hemispheres are kept apart by using a separator aperture (Fig 1).

Fig 1 

 

When the bomb has to be exploded. A third well fitting cylinder of  U²³⁵ ( whose mass is also less then critical mass) is propelled so that it will fit in or fuse together with the other two pieces. Now the total quantity of U²³⁵ is greater than the critical mass. Hence an uncontrolled chain reaction takes place resulting in a terrific explosion.

The explosion of an atom bomb releases tremendously large quantity of energy in the form of heat, light and radiation. A temperature of millions of degrees and a pressure of millions of atmospheres are produced. Such explosions produce shock wave, They are every dangerous because the waves spread radioactivity in air and cause loss of life. 

The release of dangerously radio active γ-rays, neutrons and radioactive materials presents a health hazard over the surroundings for a long time. 

The radioactive fragments and isotopes formed out of explosion adhere to dust particles thrown into space and fall back to earth causing a radiation “fall-out”, even at very distant places.

 

Positron

 

Positron, also called positive electron, positively charged subatomic particle having the same mass and magnitude of charge as the electron and constituting the antiparticle of a negative electron

Spontaneous Fission

Spontaneous Fission 

   Another type of radioactive decay is spontaneous fission. In this decay process, the nucleus will split into two nearly equal fragments and several free neutrons. A large amount of energy is also released. Most elements do not decay in this manner unless their mass number is greater than 230. 

                                                                                                                                                                                            
                                                     

                                                          Spontaneous Fission 

    The stray neutrons released by a spontaneous fission can prematurely initiate a chain reaction. This means that the assembly time to reach a critical mass has to be less than the rate of spontaneous fission. Scientists have to consider the spontaneous fission rate of each material when designing nuclear weapons.

 
   For example, the spontaneous fission rate of plutonium 239 is about 300 times larger than that of uranium 235. This forced scientists working on the Manhattan Project to abandon work on a gun-type design that used plutonium. 

Atomic Isotope

 Atomic Isotopes    

      A major characteristic of an atom is its atomic number, which is defined as the number of protons. The chemical properties of an atom are determined by its atomic number and is denoted by the symbol Z. The total number of nucleons (protons and neutrons) in an atom is the atomic mass number. This value is denoted by the symbol A. The number of neutrons in an atom is denoted by N. Thus the mass of an atom is A = N+Z.

       

                                 

                                                   Nuclear Isotopes 
     Atoms with the same atomic number but with different atomic masses are called isotopes. Isotopes have identical chemical properties, yet have very different nuclear properties. For example, there are three isotopes of hydrogen. Two of these isotopes are stable, (not radioactive), but tritium (one proton and two neutrons) is unstable. Most elements have stable isotopes. Radioactive isotopes can also be created for many elements. 

Atomic Structure

Atomic Structure 

      An atom is a complex arrangement of negatively charged electrons arranged in defined shells about a positively charged nucleus. This nucleus contains most of the atom's mass and is composed of protons and neutrons (except for common hydrogen which has only one proton). All atoms are roughly the same size. A convenient unit of length for measuring atomic sizes is the angstrom (Å), which is defined as 1 x 10-10 meters. The diameter of an atom is approximately 2-3 Å. 

     In 1897, J. J. Thomson discovered the existence of the electron, marking the beginning of modern atomic physics. The negatively charged electrons follow a random pattern within defined energy shells around the nucleus. Most properties of atoms are based on the number and arrangement of their electrons. The mass of an electron is 9.1 x 10-31 kilograms. 

   One of the two types of particles found in the nucleus is the proton. The existence of a positively charged particle, a proton, in the nucleus was proved by Sir Ernest Rutherford in 1919. The proton's charge is equal but 

opposite to the negative charge of the electron. The number of protons in the nucleus of an atom determines what kind of chemical element it is. 

      A proton has a mass of 1.67 x 10-27 kilograms. 

   The neutron is the other type of particle found in the nucleus. It was discovered by a British physicist, Sir James Chadwick. The neutron carries no electrical charge and has the same mass as the proton. With a lack of 

electrical charge, the neutron is not repelled by the cloud of electrons or by the nucleus, making it a useful tool for probing the structure of the 

atom.

      Even the individual protons and neutrons have internal structure, called quarks. Six types of quarks exist. These subatomic particles cannot be freed and studied in isolation. Current research continues into the structure of the atom. 

ATOMIC PHYSICS .Introduction to Atomic Physics

ATOMIC PHYSICS
   

     Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and the processes by which these arrangements change.

Introduction to Atomic Physics 

    Atomic energy is the source of power for both nuclear reactors and nuclear weapons. This energy comes from the splitting (fission) or joining (fusion) of atoms. To understand the source of this energy, one must first understand the atom. 

            

                                       Components of the atom

  An atom is the smallest particle of an element that has the properties characterizing that element. Knowledge about the nature of the atom grew slowly until the early 1900s. One of the first breakthroughs was achieved by Sir Ernest Rutherford in 1911. He established that the mass of the atom is concentrated in its nucleus. He also proposed that the nucleus has a positive charge and is surrounded by negatively charged electrons, which had been discovered in 1897 by J. J. Thomson. 
     
     This theory of atomic structure was complemented by Niels Bohr in 1913. The Bohr atom placed the electrons in definite shells, or quantum levels. Understanding the atom continues to be a focus for many scientists.