The Science of Electricity

  Electric Potential and Potential Difference We know that when a body is lifted through certain height above the ground level, work is done against the force of gravity and is stored as a potential energy in the body. Hence such a body which is raised above the ground level can be said to have a gravitational potential. Obviously, the total potential energy and hence, the gravitational potential of a body is a function of its position with respect to earth. Here the example is very much analogous to the Electric Field around a charge. Now consider that a small isolated positive charge q is placed at a far distance let’s say infinity with respect another positive charge Q. Theoretically the electric field of the positive charge reaches upto infinity but in the practical sense it’s influence on positive charge q which is placed at infinity is very negligible. Fig. 1 : Two isolated charges  If this charge q is shifted near to Q and brought at the same point X s

P-N Junction Diode The P-N junction itself forms the most basic semiconductor device called Semiconductor Diode. Thus semiconductor diode and the P-N junction are one and the same. The meaning of the term "diode" is the device having "two electrodes" (di-ode).  As shown in Fig. 1 , the diode has two electrodes one each for the two regions on either sides of the junction. Fig. 1: A P-N junction forms a semiconductor diode  Fig. 2 : Circuit symbol of diode Symbol of the P-N junction diode The symbol of a semiconductor diode is as shown in Fig. 2. The two electrodes (terminals) are named as anode and cathode.  The arrowhead in the symbol points in the direction of conventional current through the device. This current will flow through the diode if and only if an external voltage source is connected to it with appropriate polarities. Biasing of a P-N Junction Diode When the P-N junction is formed, the depletion region gets created and the movement of ele

Formation of P-N junction   The P-N Junction Definition : When a P-type semiconductor is suitably joined to an N-typed semiconductor under suitable condition by using special technique to form a junction, the contact surface is known as a p-n junction. The P-N junction is the basic building block on which the operation of all the semiconductor devices is dependent. The behaviour of the P-N junction is developed based on the semiconductor properties described in the  earlier posts in the semiconductor theory. Diode means a device with two elements namely anode and cathode. Since a P-N junction itself is a two element devices, it becomes the most basic electronic device i.e. the diode. 1. The Open Circuited P-N Junction (Unbiased p-n Junction)                                                       Fig. 1: Formation of a P-N junction As shown in Fig., a P-type semiconductor and an N-type semiconductor are joined together with the help of a special fabrication technique to fo

Semiconductors     Definition : The materials, whose electrical conductivity lies between those of conductors and insulators and have negative temperature coefficient of resistance, are known as semiconductors.   Semiconductor Materials : The few examples of semiconductor materials are as under : 1.Carbon (C) 2. Silicon (Si) 3.Germanium (Ge) 4. Selenium (Se) 5.Gallium Arsenide (GaAs) 6.Cadmium Sulphide (CdS). The commonly used semiconductor materials are Germanium and Silicon. These are tetravalent elements i.e. materials having  four valency.   Atomic Structures of Germanium and Silicon : (i) Atomic structure of Germanium and Silicon atoms :  Fig. 1.3 (b) shows the atomic structure of a Germanium atom  in which first, second, third and fourth orbits have 2, 8, 18 and  4 electrons respectively, with the result that the atomic  number for Germanium is 32. Fig. 1.3 (a) shows the atomic structure of a Silicon atom in  which first, second and th