RESISTIVITY OF A WIRE

Resistivity of a Wire

Resistivity of a Wire

In this paper, we will calculate resistivity of a given wire. An electron traveling 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 (www.courseworkhelp.co.uk). The rate at which charge flows from terminal to terminal is the result of the combined effect of these two quantities. The equation representing the dependency of the resistance (R) of a cylindrically shaped conductor (e.g., a wire) upon the variables which affect it is:

R = ?L/A

where L represents the length of the wire (in meters), A represents the cross-sectional area of the wire (in meters2), and represents the resistivity of the material (in ohm•meter). Consistent with the discussion above, this equation shows that the resistance of a wire is directly proportional to the length of the wire and inversely proportional to the cross-sectional area of the wire. As shown by the equation, knowing the length, cross-sectional area and the material that a wire is made of (and thus, its resistivity) allows one to determine the resistance of the wire (www.physicsclassroom.com).

Planning

Some variables that will be relevant to this investigation are:

Length

Thickness

Temperature

Voltage

Resistance

Material

Method

First a length of wire over a metre long is sellotaped to a metre rule. The positive crocodile clip is attached at 0cm. And the negative is moved up and down the wire, stopping at 20, 40, 60, 80 and 100cm. Each time reading the ammeter and voltmeter to work out resistance R = V/I. This is using 30 SWG wire. Other variables, voltage, thickness, and temperature will be kept constant, although the temperature will rise once current is passing through it, which will cause the atoms in the wire to vibrate, and so obstruct the flow of electrons, so the resistance will increase, creating an error. In this experiment constantan wire is used because it does not heat up as much as copper, so the resistance is not effected as much (www.courseworkhelp.co.uk).

Results

Experiment 1

Length (cm)

V1 (volts)

V2 (volts)

A1 ...