# Resistance of a Wire Coursework

Topics: Electric current, Electricity, Ohm's law Pages: 4 (1528 words) Published: November 14, 2006
The problem with using resistance as a measurement is that it depends not only on the material out of which the wire is made, but also the geometry of the wire. If we were to increase the length of wire, for example, the measured resistance would increase. Also, if we were to decrease the diameter of the wire, the measured resistance would increase. We want to define a property that describes a material's ability to transmit electrical current that is independent of the geometrical factors. The quantity that is used is called resistivity and is usually indicated by the Greek symbol rho*, **.

In the case of the wire, resistivity is defined as the resistance in the wire, multiplied by the cross-sectional area of the wire, divided by the length of the wire. The units associated with resistivity are thus ohm.m (ohm - meters). Resistivity is a fundamental parameter of the material making up the wire that describes how easily the wire can transmit an electrical current. High values of resistivity imply that the material making up the wire is very resistant to the flow of electricity. Low values of resistivity imply that the material making up the wire transmits electrical current very easily. Resistance

An electron travelling through the wires and loads of the external circuit encounters resistance. Resistance is the hindrance to the flow of charge. For an electron, the journey from terminal to terminal is not a direct route. Rather, it is a zigzag path which results from countless collisions with fixed atoms within the conducting material. The electrons encounter resistance - a hindrance to their movement. While the electric potential difference established between the two terminals encourages the movement of charge, it is resistance which discourages it. The rate at which charge flows from terminal to terminal is the result of the combined effect of these two quantities.

Variables Effecting Electrical Resistance
The flow of charge through wires is often...