The Resistance of a Wire

The Resistance of a Wire

Planning

These are the four factors that can affect the resistance of a wire.

How thick the wire is How long the wire is

Factors that can affect

resistance

The heat of the wire What the wire is made of

Background theory

In metals the molecules are usually single atoms and electrical forces

hold these together. The atoms are packed tightly together in a

regular pattern and electrical forces hold these together. The tight

packing causes outer electrons to get separated from their atoms. This

is the reason why metals are good conductors of electricity as the

electrons are free to carry charge.

When a voltage is applied across a wire, the electrons drift through

the metal. It is an unsteady motion as the electrons continually

collide with the ions. The electrons accelerate, collide with the ions

and stop. However, because there is a voltage going across the wire

they accelerate again until they reach another ion. The movement of

the electrons is a stop-start process. So the ions cause the

resistance of the wire.

For a constant length of wire, if we double the diameter, as shown

below:

The area increases 4 times. This means that the voltage will affect

four times the number of electrons. The current will increase and the

resistance will decrease.

Source - Co-ordinated Science - Chemistry textbook page 50

Prediction

I predict the resistance of the wire will decrease as the

cross-sectional area of the wire increases. I predict that doubling

the area will half the resistance.

Fair testing

Throughout the investigation the following will not change:

* Temperature (room temperature)

* Length of wire

* Material of wire

Number of measurements

I shall measure the resistance of 5 different wires, each of a

different diameter. I will then repeat the reading and find the

average in each case.

Apparatus