What effects the resistance of a piece of wire?

Here is a diagram to show this:

To carry out my experiment I will need:

* An ammeter measured to the nearest 0.2A

* A variable resistor

* A voltmeter

* 100cm of Nichrome wire

* A powerpack

* Crocodile holders for the wire

Here is a diagram of how I will set up my experiment:

As a safety precaution for this experiment I will keep the current between 0.1A and 0.3Ato make sure that the wire doesn't get to hot.

To make sure that this is a fair test I will have to keep all of the variables the same apart from the length, all the way through the experiment. This is because if I changed the other variables the results wouldn't show how just the length of the wire effects the amount of resistance.

A brief method for how I will do the experiment is:

. Set up the equipment as shown in the diagram.

2. Measure the maximum length of the wire.

3. Carry out the experiment with the current set between 0.1A to 0.3A. Place the different sized wires between the crocodile clips, switch on the current and take the voltage three times. Then work out the average voltage and use the equation:

R=V/I

R=resistance, V=voltage, I=current

To work out the average resistance.

Here is a table to show the results of my experiment:

To do the experiment first I had to set up my equipment in the correct way then I measured the maximum length of wire, which was 100cm. Then I did the experiment by placing the wire in the crocodile clips and switching the power on. Before I took any readings I made sure that the current on the ammeter was at 0.2A as a safety precaution to make sure that the wire didn't get too hot and also to make the experiment a fair test. To adjust the current on the ammeter I had to adjust the variable resistor slightly. When everything was correct I took the voltage 3 times and worked out the average voltage. I took the voltage 3 times so that I could work out the average voltage which would make my results more reliable, because if I only took the voltage once there may have been a mistake so my results would have been incorrect. I repeated this for every 10cm of the wire. Then I worked out the resistance by using the equation:

R=V/I

My results from the experiment are shown in the table.

Here is a graph to show my results:

In this experiment I discovered that if I doubled the length of a piece of wire the amount of resistance would also be doubled.

In the graph it shows that there is a line of best fit. The last three results are slightly out of the line though. The results increase as the amount of wire increases which shows that if the wire is longer there is more heat energy being produced by the ions and electrons meaning the resistance would be higher.

Evaluation

When I did my experiment I found that when I set my experiment up I put a wire in the wrong place in the ammeter so the dial went the wrong way so that we couldn't set the current to the right place. We overcame this problem by taking the wire out and putting it in the other way.

My measurements are quite accurate because on the graph the results all line up, part from a few results at the top of the graph. This may be because I might have measured the wire slightly wrong so the wire would be a little bit longer or shorter than it should have been which would effect the amount of resistance produced.

My prediction was that if I doubled the wire the resistance would also double. Because if the wire was double the length there would be twice as many ions and electrons, meaning that there would be two times as many collisions between the ions and electrons making twice as much resistance produced. My prediction was quite accurate I found this out because the result for a 5cm piece of wire is roughly half of the results for a 10cm piece of wire. The differences in the line of best fit may be due to incorrect measuring of