Here are the results for my pilot experiment:

## The Material

Firstly I had to find out which material I should use for my experiment copper and constantan.

I decided to use constantan because it has a bigger resistance and therefore I will get a larger range of results

The Width of Constantan

I would use a size 28 (swg) for the actual experiment because it is not too small and not too big. It also does not give off any heat so not as much heat would be lost in the experiment and my results will not be disrupted.

## The Length of Constantan

I decided to have a range of the length of wire from 0 cm-100 cm in the actual experiment to make the experiment fair. I would also keep the potential divider the same and not move it to make the experiment fair. Also take make the experiment fair I did it in one lesson and kept the same equipment. If I changed the equipment or anything else my results would be distorted and wrong.

My Chosen Variable

After performing my pilot experiments I decided to use “Changing the Length of the Wire” as my variable because it is not a very complicated procedure but on the other hand, “Changing the temperature of the wire” is time consuming and very hard to do.

Prediction:

I predict that if I should alter the length of the wire or the thickness of the wire then the resistance should also change. For example if I increased the wire length then the resistance would increase and if I decreased the wire length then the resistance would also decrease, I will explain this in my theory. The resistance should double as the length doubles e.g. 10cm-1Ω, 20cm-2Ω and so on.

Theory:

As the electrons drift down the wire they bump into the lattice ions and bounce off. This causes the resistance of the wire. When the electrons bump into the ions they pass some energy to the ions that vibrate through bigger amplitude. I predict that if the length or thickness of the wire is increased then, because there are more lattice ions for the electrons to bounce off, the resistance will be greater. I predict that if the length or thickness of the wire is decreased then, because there are less lattice ions for the electrons to bounce off, the resistance will be smaller.

Here is a diagram to show my theory:

Apparatus

Here is a diagram of the equipment that I used to conduct the experiment:

The following is a list of the equipment that I needed to use to conduct my experiment:

∙ A power pack.

∙ Power leads.

∙ An ammeter.

∙ A voltmeter.

∙ A variable resistor. I chose this because a fixed resistor can only take one reading and a variable resistor can take a number of readings.

∙ Meter ruler. This was to measure the length of the wire and to ensure that the length between each crocodile clip was correct e.g. 20 cm.

∙ Crocodile clips. These were to secure the wire in place.

∙ Wire e.g. constantan or copper.

Textbooks

For my coursework I used the following textbooks for my research:

####
Key Science, by Jim Breithaupt (Third edition)

Physics, by Genzer and Phillip Youngner

College Physics, Serway and Faughn

###
Method for Changing the Length of a Wire

#### The method for this experiment was as follows:

#### ∙ Firstly I had to set up the apparatus as shown above and check that it works properly.

#### ∙ Measure the appropriate length between each crocodile clip e.g. 10 cm.

#### ∙ Switch the power pack on to “direct current”, (D.C.) and 2 volts.

#### ∙ Take a stable reading from the ammeter and the voltmeter.

#### ∙ After each reading switch the power pack off so the wire does not over heat and disrupt you readings

#### ∙ Continue to take readings until you have reached the highest length required. Remember to measure carefully and accurately.

####
∙ Calculate the resistance of the wire in a column next to your results table. Use V=IR (Voltage =Current×Resistance)

#### ∙ Construct a graph to show your results

To keep the constants the same throughout the experiment; make sure that the length between the crocodile clips is accurate; turn the power pack off to decrease the heat of the wire; do the experiment in one lesson so that the readings are not disrupted and use the exact same apparatus for each experiment also so the experiment is not disrupted.

Obtaining Evidence

### Results

Tables:

#### Please see extra sheet for tables, repeats and averages.

##### Analysis

#### Please see extra sheet for the graph

##### Analysis:

From the results I constructed a graph showing how the resistance of a wire changes with the length. Because the graph shows a straight line, (If my results were correct) the resistance of the wire is directly proportional to the length of the wire. The results from the graph give a clear indication of how the resistance compares to the wire length. There is a very strong positive relationship. My results show that I expected to see these results because as the length of the wire increases, the resistance of the wire increases therefore; the graph should show a straight. An example would be at a wire length of 50 cm, the resistance is 2.90 ohms and at 100 cm it is 6.00 Ohms. This shows that if you double the length the resistance almost doubles as well.

Theory

The theory is partly explained in the prediction. In all metal wires there are millions of moving electrons. The reason that they move is because of electricity. The resistance of a wire is caused when atoms that make up any object slow the electrons down. This means that if there are more atoms to get in the electrons way (e.g. length or the width is increased) the resistance is then increased. If there is twice the length of the wire, then there will be twice the resistance. This will lead to there being double the number of collisions between the electrons and the atoms increasing the resistance by 2. If there are 250 atoms blocking electrons in a 5 cm length wire then (according to my theory) there will be 500 atoms blocking electrons in a 10 cm length wire. My theory explains why the results were directly proportional.

My results that I have collected support my prediction because I said that if I increased the wire length then the resistance should increase and if I decreased the wire length then the resistance should also decrease.

The results have shown that this is true. My graph of results shows that the line of best fit has followed the predicted pattern and that, although one point is very slightly anomalous to the rest, the gradient of the line stayed the same throughout.

Evaluation

Accuracy:

From looking at my graph of results I can see that none of my points are extremely anomalous. This shows that my results are accurate and that my apparatus which I used was also accurate