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Adeel Malik 11/g December 2002 Aim The aim of this experiment is to investigate how the resistance of a wire changes in relationship to its length. We will increase the length of the wire and measure the voltage and current, and then calculating the resistance. Prediction I think that as the length of the wire increases so will the resistance of it. I also believe that the rate at which the length of the wire is increased, the resistance of the wire will also increase in direct proportion to the length. The graph to show this should therefore look something like this: A graph to show the relationship between resistance of a wire and it’s length. The resistance of the wire is directly proportional to the length of it. Theory With electricity, the property that transforms electrical energy into heat energy, in opposing electrical current, is resistance. In a conducting material a property of the atoms is that they have free electrons in the outer shell of their structure. All metals are conductors and have an arrangement in similar form to this: As a result of the structure of all conductive atoms, the outer electrons are able to move about freely even in a solid. When there is a potential difference across a conductive material all of the free electrons arrange themselves in lines moving in the same direction. This forms an electrical current. When current is passed through a conductor, the electrons move from areas of high potential (i.e. the negative terminal of the power source) to areas of low potential (i.e. the positive terminal of the power source. Flow of electrons from negative to positive Resistance is created when the negatively charged particles that make up the current, collide with other fixed particles in the material. As the resistance of a material increases so to must the force required to drive the same amount of current. In fact resistance, in ohms(R) is equal to the electromotive force or potential difference, in volts (V) divided by the current, in amperes (I) – Ohm´s law. R=V/I As the length of the wire is increased the number of collisions the current carrying charged particles make with fixed particles also increases and therefore the value for the resistance of the wire becomes higher. Resistance, in ohms (R) is also equal to the resistivity of the wire, in ohm-meters (ñ) multiplied by the length, in meters (l) divided by the cross sectional area, in square meters (A). R= n x l/a Any solid material is made up of atoms, packed up closely together in a structure. If electrons are flowing through the material (i.e. it is being used as a conductor) it is likely that all, of them will, at some point on their journey through the material, hit one or more of the atoms in the material, and so get slowed down.
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