Good conductors are associated with low resistance and poor conductors are associated with high resistance. As resistance is responsible for the current that flows, a high resistance will be responsible for a low current and a low resistance will be responsible for a higher current. This is definition of resistance given by Hutchinsons Encyclopaedia:In physics, that property of a conductor that restricts the flow of electricity through it, associated with the conversion of electrical energy to heat; also the magnitude of this property. Resistance depends on many factors, such as the nature of the material, its temperature, dimensions, and thermal properties; degree of impurity; the nature and state of illumination of the surface; and the frequency and magnitude of the current.
The SI unit of resistance is the ohm (U). Resistors are devices, as a coil or length of wire, used in a circuit primarily to provide resistance. ResistorIn physics, any component in an electrical circuit used to introduce resistance to a current. Resistors are often made from wire-wound coils or pieces of carbon.
Rheostats and potentiometers are variable resistors. Prior knowledge and Internet research indicates that a Georg Simon Ohm was one of the forefathers of research into electrical resistance. Ohm, Georg Simon Ohm, Georg Simon, 1789-1854. German physicist best known for Ohm’s Law, the basic law of current flow.
Educated in science by his father, a master locksmith, he worked as a schoolteacher before deciding to devote himself to research in physics. He began the studies leading to the formulation of his law in 1825 and discovered that the force of a current traveling through a conductor is a measure of the current. The resulting Ohm’s Law was the earliest theoretical study of electricity. The unit of resistance (ohm) and unit of conductivity (mho–ohm spelled backward) are named for him. (Extracted from Comptons Home Library 1998)E = Electromotive force(Volts)I = Current(Amps)R = Resistance(Ohms)Figure 1-1 The most common definition of Ohms Law. The most common definition of Ohms Law is given in Figure 1-1.
Actually, it is not an expression of Ohms Law; it simply defines resistance. Starting from any section of the triangle, this can be read in any direction – clockwise, anti-clockwise, top to bottom or bottom to top – and it will always provide the calculation you require. If the horizontal lines are treated as divide signs and the short vertical line as a multiply sign, and the calculation is started with whatever quantity that is looked for, i. e.
; “V=”, “I=” or “R=” all possible formulae based on this particular Ohms law will be attained. That is; V=IxR, I=V/R, R=V/I. It should be apparent that the formula works the other way too, that is; IxR=V, RxI=V, V/I=R and V/R=I. Ohms Law is defined as; “Provided that the temperature remains constant, the ratio of potential difference (p.
d. ) across the ends of a conductor (R) to the current (I) flowing in that conductor will also be constant”. Orthe current passing through a wire at constant temperature is proportional to the potential difference between its ends. From this, we conclude that; Current equals Voltage divided by Resistance (I=V/R), Resistance equals Voltage divided by Current (R=V/I), and Voltage equals Current times Resistance (V=IR). The important factor here is the temperature. If calculations based on Ohms law are to produce accurate results this must remain constant.
In the ‘real’ world it hardly ever does, but shall not prove a significant threat to result accuracy if precautions are taken. Ohms Law only applies to metallic conductors.