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Analog electronics and applications
Conductors, semiconductors and holes as charge carriers
Topics covered in this lecture
D. Intrinsic semiconductors
Conductors: A conductor is the name of a material which is a good conductor of electricity. Copper ( Cu ), Silver ( Ag ) and Gold ( Au ) are examples of materials which are good conductors of electricity, in other words they are known as conductors.
A natural question arises as to why copper is a good conductor of electricity. Such a fact can be understood from its electronic configuration.
Electronic configurations are a good way to understand the physical as well as chemical properties of materials. A great deal of our modern understanding of materials and their properties are based on the detailed electronic configuration facts of the same.
The copper has 29 electrons in its atom. That means it has an equal number of protons. It has two isotopes, one has 34 and the other has 36 neutrons. Isotopes are the same chemical element having 2 or more than 2 different types of nuclei, due to difference in the number of neutrons. As a whole copper atom is electrically neutral.
The 29 electrons are distributed into shells or orbits. Consequently the first orbit has 2, 2nd orbit has 8 and 3rd orbit has 18 electrons. There is only 1 electron in the outermost orbit of the copper atom.
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Fundamental types of crystal lattices and their symmetry operations.
a. Types and classes of crystals,
b. Symmetry operations in crystals
In this lecture we will follow through our basic knowledge gained in the last lecture. — lecture — I, II, and shed light on the most interesting properties of crystal lattices, viz. their symmetry properties. Based on their properties we will classify them into various types and classes.
ii. Lattices satisfy additional symmetry operations. But due to the constraint of translational symmetry the total number of symmetry operations that the lattices can satisfy is reduced to a minimum.
iii. This means in 2-dimensional lattice constructs we have only 5 types of lattices which satisfy additional symmetry operations. In 3-dimensional geometry there are a total of 14 classes of lattices.
iv. Thus in 3-dimensional lattices the 14 classes of Bravais lattices are categorized into 7 types or systems of fundamental lattices.
v. The extra symmetry operations are
inversion about a space point and
reflection about a plane passing through a lattice point or
their possible combinations.
Electromagnetic theory, lecture — IV
Topics covered in this lecture
a. Helmholtz theorem — in electrodynamics
b. Gauge transformation — of scalar and vector potential in electrodynamics
c. Coulomb and Lorentz gauge
All electromagnetic theory lectures of this series, will be found here (https://mdashf.org/category/electromagnetic-theory/)
In our previous lecture — lecture — III, we discussed in quite detail, the problem of electrostatics and magneto-statics.
We understood how deeply the Helmholtz theorems formulate the entire question of these two branches of electromagnetic phenomena.
But static problems are not sufficient for any rigorous treatment of the electromagnetic theory.
We promised in that lecture to study how Helmholtz theorems lend their magical power to understand the most general nature of electromagnetic phenomena.
In this lecture we will study precisely the applicability of Helmholtz theorems to the problem of electrodynamics and we will see how it leads to a great deal of success in advancing the ability to solve electromagnetic problems of a great variety.