ELECTRICAL ENGINEERING

Effect of Temperature on Resistance     we have explain erlier (Law of Resistance) that resistance of the conductor dipending on temprature. so that, here we will show you the effect of rise in temperature:     1) to increase the resistance of pure metal. The increase is large and fairy regular for normal ranges of temperature. The temperature/resistance graph is a straght line (figure 1).     2) to increase the resisrance of alloys, though, in their case, the increase is relatively small and irregular. for some high-resistance alloys like eureka (60% Cu and 40% Ni) and manganin, the increase in resistance is negligible ove a considerable range of temperature.    3) to decrease the resistance of electrolytes, insulators (such as paper, rubber, glass, mica, etc.) and partial conductors such as carbon. hence, insulators are said to prossess a negative temperature-coefisient of resistance. figure 1 ( The temperature/resistance graph) Temperature-Coefficient of Resistance

Law of Resistance Every conductor has resistance that depending on the following factors:     1). it varies direcly as its length, l     2). it varies inversely as the cross-section A of the conductor.     3). it depends on the nature of material.     4). it depending on the temperature of the conductor. Ignoring the last factor fo the time being, we can say that: where: "R" is resistance of the conductor (ohm) "READ : The Unit of Resistance " "l" is the length of the condutor (metre) "A"  is the area of cross section of the conductor (metre^2) is a constant depending on the nature of the material of the conductor known as its specific resistance or resistivity, that will be discussed in Unit of Resistivity from the equetion above, we will know how to get good conductor. good conductors those with little resistace. "READ ALSO: good resistance in Modern Electron Theory ".  statemen 1 the longger the

   The practical unit of resistance is Ohm. A conductor is said to have resistance of one ohm if it permits one ampere current to flow through it when one volt is impressed  across its terminals. Ohm The symbol of ohm is shown below. the ohm symbol Table (multiples and submultiples of Ohm)     For insulator whose resistance are vey high, a much bigger unit is used i.e, mega-Ohm = 10^6 ohm (the prefix 'mega' or 'mego' meaning a million) or kiliohm=10^3 ohm (the prefix 'kilo' meaning thousand). in the case  of vey small resistance , smaller units like miliohm = 10^-3 ohmor microohm = 10^-6 are used. Read also: Resistance  

Figure 1     It may be defined as the property of a substance due to which it opposes the flow of electricity ( Read: The Ide of Electric Potential ) throug it.       Metal (as a class), acids and salt solutions are good conductors of electricity. amongst pure metals, silver, copper, and aluminium are vey good conductors in the given order. This, as discussed earlier (Read: Modern Electron Theory ) , is due to the presence of a large number of free or loosely-attached electrons in their atoms. These vagrant electrons assume a derected motion on the application of an electric potential difference. These electrons while flowing pass throug the molecules or the atoms of the conductor, collide with other atoms and electrons, thereby producing heat.                Figure 2 metal  ( https://www.imperiummultiniaga.com)    Figure 3 copper ( http://www.hoo-tronik.com)     These substances which offer relatively greater difficulty or hindrance to the passage of these elec

     In figure. 1 below is shown a simple voltaic cell. it consists of a copper plate (known as anode) and a zinc plate ( i.e. cathode) immersed in dilute sulphuric acid (H2SO4) contained insuitable vessel. Figure 1 the chemical action taking place within the cell causes the electrons to be remove from Cu plate and to be deposited on the zinc plate at the same time. Thsis transfer of electrons is accomplished through the agency of the diluted H2SO4 which is known as electrolyte. The result is that zinc plate becomes negative due to the deposition of electrons on it and the Cu plate becomes positive due to the departure of electrons  from it. The large number of electrons collected on the zinc rod is being attracted by anode, but is prevented from returning to it by the force set up by the chemical action within the cell. But if the two electrodes are joined by wire externally, then electrons rush to the anode, thereby equalizing the charges of the two electrodes. however due to

     Modern research has ebtablished that all matter whether solid, liquid, or gaseous, consists of minute particles called molecules which are them selves made up of still minute particles known as atoms. Those substances whose molecules consist of similar atoms  are known as elements (as shown in figure 1) Figure 1 (  http://gb.scientificgems.wordpress.com/) and those whose molecules consist of dissimilar atoms are called compounds (as shown in figure 2).  Figure 2 (https://prodiipa.wordpress.com/) An atom is taken to consist of the following:  1).  It has a hard central core known as nucleus. It contains two types of particlesor; one is known as proton and carries positive charge, the other is neutron (discovered by Chadwick in 1932), which is electrically neutral i.e. it carries no charge though it is as haevy as proton. The protons and neutrons are very closely held together with tremendous forces.  2). Revolving round the relatively massive nucleus, in more or

    It is comparatively easy to discribe what electricity can do than to give simple and direct answer to the question:   what exactly is meant by electricity?. Electricity has become such a universal medium for transmission and utilization of energy that almost evey one familiar with its innumerable uses right from the earliest chilhood. Electric energy is variouly utilised as for lighting, transportation, communication, for operating electric furnace, elevator, and for driving various kinds of machine tools ect. It can easily stored and concentrated to produce extremely high temperature as in welding and electric furnaces, acr light and spark plugs etc.    Turning back to the question regarding the nature of electricity, it maybe noted that ancient Greeks were the first to observe that when Amber,it is a yellow brown gum that hardens into hard stone-like material , is rubbed against a piece of silk cloth, it attracts light objects like small pieces of paper etc. The agency that