In this article we will discuss about:- 1. Introduction to Free Electron Theory 2. Electrical Conductivity as per Free Electron Theory 3. Limitation. Introduction to Free Electron Theory: According to Drude, the metals consists of positive ions cores with the valence electrons moving freely among these cores. The electrons are, therefore bound to move within the metal due to electrostatic [...]
In this article we will discuss about the possible electronic states of electrons in the potential energy box (one dimensional as well as three dimensional) and their distribution using quantum theory. The Fermi-Dirac distribution allows only a fraction of the total number of free electrons to gain energy and the values of heat capacity and paramagnetic susceptibility thus obtained coincide [...]
In Kronig-Penny model, it is assumed that the potential energy of an electron in a linear array of positive nuclei has the form of a periodic array of square wells (Fig. 5.10). Let the period of the periodic potential be (x + b). For -b < x < 0 the potential energy is V0 while for 0 < x < [...]
In this article we will discuss about:- 1. Meaning of Thermal Conductivity 2. Wiedemann Franz Lorentz Relation of Thermal Conductivity 3. Heat Developed 4. Thermionic Emission. Meaning of Thermal Conductivity: We know that in a solid, atoms vibrate about their equilibrium position at ordinary temperature and the amplitude of vibration decreases to a minimum at absolute zero of temperature. This [...]
The electrical conductivity σ (= 1/ρ) of a material is not constant. The factors which affect the value of conductivity σ of a material are: 1. Temperature 2. Alloying atoms 3. Mechanical stress 4. Age Hardening. 1. Effect of Temperature: We know that the resistance of most of the conducting materials increases with temperature. The change in resistance of a [...]
According to de-Broglie, the motion of an electron with a velocity v is equivalent to the motion of a wave packet with group velocity vg. The velocity of free electrons is proportional to k. Now on the basis of band theory, the variation of E with k is shown in Fig. 5.15 (a). Since the curve is symmetrical having points [...]
In this article we will discuss about the classical picture of energy bands in solids. For the transition of an electron from the inner orbit to the outer orbit of the atom, some energy is required. Thus, the different orbits have the different levels of potential energy. In an atom, the electrons try to occupy the inner orbit (having minimum [...]
In this article we will discuss about the thermo-electric effect and its applications in generating electricity. Thermo-Electric Effect: Thermoelectric is the phenomenon in which the heat energy is converted into electric energy or vice-versa i.e. Heat energy ⇋ Electric energy. As we are well aware that the Joule heating effect proceeds only in one direction; reversal of the current has [...]
In this article we will discuss about the measurement of conductivity using four probe method. After a semiconductor material is grown, it is ofcourse vital to determine its usefulness for device fabrication. There are several properties which have a strong effect on the final characteristics of diodes and transistors made from single crystal of semiconducting material. Most important of these [...]
In this article we will discuss about:- 1. OHM'S Law 2. Mean Free Path (L) 3. Relaxation Time 4. Factors Affecting Resistivity of Metals 5. Low Resistivity Conducting Material 6. High Resistivity Conducting Material 7. Insulating Materials 8. Application of Conductors 9. Types of Conducting Materials. OHM'S Law (Point Form): When an electric field is applied to a conductor, the [...]