What Factors Affect the Resistance of a Wire?

What Factors Affect the Resistance of a Wire?

Planning

Background

Electricity flows around a circuit in a current. A current is the flow of electrons. Currents are measured in amps.

Voltage is the force which pushes electricity through a wire. Voltage comes from a cell or a socket. Voltage is measured in volts.

Electrical resistance is a measure of the degree to which a body opposes the passage of an electric current. (en.wikipedia.org/wiki/Resistance(electricity). Resistance is a force that slows down the flow of electricity.

Resistance is calculated by:

R = V/I

R = resistance, I = current and V = voltage. This is called "Ohm's Law". To find the resistance you need to have the current and the voltage. Resistance is measured in ohms (Ω).

Resistance of a wire can be affected by different things. They are what the wire is made out of, the length of the wire, the temperature of the wire and how thick the wire is.

If I change what the wire is made of it will affect the resistance of the wire because different substances conduct electricity in different ways.

If I change the length of the wire it will affect the resistance of the wire. This is because the current, with the electrons in it, will have to travel further. When current moves through a wire it "bumps" into the metal ions that make up the wire. This "bumping" (or collisions) causes resistance.

If I change the thickness of the wire it will affect the resistance of the wire because the electrons have more room to move around in the wire and there are less collisions and less resistance.

If I change the temperature of the wire, for example make it hotter, the electrons will vibrate more. This will make it harder for the electrons to travel through the wire as there is more chance of collisions.

The things I can look at and measure are the length of the wire, the thickness of the wire and the temperature of the wire. These things are also called variables but because I am not going to change them they are called dependent variables.

In my experiment I have decided to change the length of the wire. This will be my independent variable.

Prediction for preliminary work

I think that if I make my wire longer the resistance will increase. This is because the electrons in the wire have further to travel if the wire is longer. As the move along the longer wire they will collide with more metal ions. These collisions will mean that the electrons will lose both movement and heat energy and be slowed down.

Preliminary work

I measured three lengths of wire. I put them into three circuits. I turned on the power at 2V and recorded the readings on the volt and ammeters. I put my results into a table.

Length of copper wire Volt meter reading (V) Current reading (A) Resistance (Ω)

10cm 0.17 6.44 0.03

20cm 0.27 5.95 0.05

30cm 0.31 5.80 0.05

The first thing you can see from my preliminary work is that it is hard to work anything out from my results. The resistance is more when the wire length is changed from 10cm to 20cm but there is no change in the resistance when the wire is increased to 30cm. I decided that I would need more results before I could be sure that my results were reliable. I decided to do five different lengths of wire and repeat each test three times. This would give me a bigger range of results from 10cm to 100cm.

I noticed that if I left the power pack on the wire got hot. I decided that I would turn the pack on very quickly and record the first results otherwise my results might be affected by heat and be unreliable. I also decided that I would use a stop watch so that I could be sure that I let my wire cool down for the same amount of time each time.

Hypothesis

I am going to look at what things affect the resistance in a wire. The main things which can affect the resistance of a wire are:

What the wire is made out of, the length of the wire, the temperature of the wire and how thick the wire is.

Plan

Using the things I had learnt in my preliminary work I designed an experiment to find out if the length of the wire affects resistance. I decided that I would build a circuit and test the resistance of copper wire. I would use different lengths of copper wire and my range would be from 10cm to 100cm.

In my preliminary work I only used three lengths of wire. This meant that I could not really tell much from my results. The next thing I planned was that I would test 5 different lengths of copper wire and