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Resistance of Wire

Essay by   •  December 5, 2010  •  Research Paper  •  6,826 Words (28 Pages)  •  2,785 Views

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Introduction

The purpose of this investigation is to expose the factors responsible for affecting the resistance of a wire in an electrical circuit. Many factors will have to be investigated prior to experimentation. A prior knowledge of electrical circuits and the factors of resistance will be required. The conclusive objective will be that research on the subject matter is proven by experimentation.

Resistance

The standard opinion of resistance when electricity is concerned is the ability of a substance to resist the flow of electricity through it. 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 Hutchinson's 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 (Ω). Resistors are devices, as a coil or length of wire, used in a circuit primarily to provide resistance."

Resistor

In 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 Ohm's 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".

Or...the 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.

Ohm's Law only applies to metallic conductors.

A more useful demonstration of Ohms Law is given below in Figure 1-2.

Figure 1-2 A grid demonstrating how to calculate resistance

It enables many more equations to be applied for calculating electrical resistance but still only applies to materials that obey Ohms Law (metals).

The circle below in figure 1-3 is another example.

Figure 1-3 A resistance calculating Crop Circle Formation produced by E.T.

Figure 1-3 demonstrates how complex as the calculating with resistance becomes. The chart above gives the formulas for many equations for making calculations about resistance. However, it is not suspected that many or even several of these formulas will be required in this investigation. The triangular series of formulas featured earlier is the most probable method to be used as it simple and easy to calculate.

This is how Ohm's Law would be applied into this hypothetical equation. Metal wires usually obey Ohm's Law. If a potential difference of 1.5V causes 3A of current to flow in a wire, how much current will flow when 6V is applied?

Voltage and current are proportional --- the voltage is multiplied by a factor of 4 so the current is also multiplied by 4: 12A of current will flow.

Find the electrical resistance of a light bulb, which passes 2A of current when a potential difference

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