The resistance of a wire.

Kieren Phillips.

Physics Coursework.

Before starting my coursework I have decided to choose a factor that will affect the resistance of a wire. I shall do this by going through all of the factors that affect the resistance of a wire and how I would measure each factor to find out which would be the most effective and easiest factor to measure. Below is a list of factors and reasons why they affect the resistance of a wire. From this list of factors I will pick one factor to investigate.

Factors
1.Temperature: If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance.
2.Material: The type of material will affect the amount of free electrons, which are able to flow through the wire. The number of electrons depends on the amount of electrons in the outer energy shell of the atoms, so if there are more or larger atoms then there must be more electrons available. If the material has a high number of atoms there will be high number of electrons
causing a lower resistance because of the increase in the number of electrons. Also if the atoms in the material are closely packed then the electrons will have more frequent collisions and the resistance will increase.
3.Wire length: If the length of the wire is increased then the resistance will also increase as the electrons will have a longer distance to travel and so more collisions will occur. Due to this the length increase should be proportional to the resistance increase.
4.Wire width: If the wires width is increased the resistance will decrease. This is because of the increase in the space for the electrons to travel through. Due to this increased space between the atoms there should be less collisions.

To choose which factor I am going to investigate I am going to consider how I would measure each factor and which factor would be the best and easiest to record.

To measure the wire width I would use different widths of the same length and same material of wire e.g. thin, medium and thick copper wire with thin and thick adjustable wire. To record the difference in widths I would use the same voltage and measure the resistance for each thickness. Although it would be easy to obtain and record the data the graphs that I would be able to draw up would not be
interesting.
For the temperature of the wire I would not be able to carry out a fair test because it is extremely difficult to produce and control the range of temperatures needed without the correct equipment.
If I chose to measure the difference in the resistance in different materials I would chose a number of different materials and using the same voltage I would record the resistance given by each wire of the
same length and width. Although once again it would be simple to record these results the graphs that could be drawn would not show any connection between the material and the resistance because of the limited number of materials I could test with the equipment available.
The final factor is the length of the wire. To measure and record the findings for this factor would be simple and the results collected could show a connection between the length of the wire and the
resistance given by the wire. This is why I have chosen to investigate this factor.

Plan.

In this investigation my aim is to investigate how the length of a wire affects the current and resistance of a wire.

Scientific Knowledge.

Metals conduct electricity because the atoms in them do not hold on to their electrons very well, and so creating free electrons, carrying a negative charge to jump along the line of atoms in a wire. Depending on the material of the wire the number of atoms it contains will vary. When the electrons of a circuit are travelling along the wire and they collide with the atoms of the wire the flow of ...

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Plan.

In this investigation my aim is to investigate how the length of a wire affects the current and resistance of a wire.

Scientific Knowledge.

Apparatus.

I will need: -

1 x 1.6 volts cell, to supply power.

3 x wires to connect and to complete the circuit.

2 x crocodile clips, to connect the wire being investigated to the rest of the circuit.

1 x Ammeter, to measure the current of the circuit in amperes.

1 x metre stick, to accurately measure the length of the adjustable wire.

1 x 100 cm adjustable wire, to conduct electricity.

Sticky tape.

Range.

For this experiment I will use a range that is suitable and reliable to my requirements. I will use a range of 15cm - 90cm with 15cm intervals for the length of the wire and use a safe voltage of 1.6 volts.

Prediction.

I predict that as I increase the length of the adjustable wire then the resistance will also increase in proportion to the length of the adjustable wire. I think this because the longer the adjustable wire the more atoms it has and so the more likely the electrons are going to collide with the atoms in the wire. Therefore if the length of the wire is doubled the resistance should also double. This is because if the length of the wire is doubled the number of atoms in it will also double resulting in twice the number of collisions slowing the electrons down and increasing the resistance. My graph hopefully should show that the length is proportional to the resistance.

Method.

This is my method for this investigation: -

1. First I collect my listed equipment and then arrange my apparatus as shown in the diagram:

Ammeter. 1.6 volt cell.

Crocodile clips.

Crocodile clips. Adjustable wire.

Metre stick.

2. I will then attach the crocodile-clips to either end of the wire of length 15cm.

3. Next I will take the reading from the ammeter and record down the current in my results table.

4. I will then repeat these steps another 5 times adjusting the length of the adjustable wire by 15 cm each time.

5. Next I will calculate the averages of the current for each length and then I will work out the resistance for each length using the formula V÷I=R (Voltage ÷ Current = Resistance).

Fair Testing.

In order for this investigation to be as fair as possible I must ensure that the thickness of the wire, material of the wire and the temperature of the wire are kept constant throughout. I must use the same cell and voltage (1.6volts) throughout. I must ensure. I must ensure that I use the same ammeter for every length and the equipment should be kept the same throughout. The only change I will make is to the length of the adjustable wire.

Safety

In order for the investigation to be safe I must: -

Handle the power supply carefully.
Be careful when touching the wire, as it may be hot.
Be careful when the wire is connected, as it will get hot.
Be careful when adjusting the length of the wire.
Make sure the mains to the power supply are switched off when removing the wire from the circuit to be measured.
Keep my work area clean and tidy to avoid confusion.

Obtaining the Information.

A = Average

Analysis.

From my results in the table I can see that as I increase the length of the wire the resistance also increases. From my graph I can see that the resistance of the wire is proportional to the length of the wire. I know this because the line of best fit is a straight line showing that if the length of the wire is increased or doubled then the resistance of the wire will also increase or double.

In my prediction I said that if the length increases then the resistance will also increase in proportion to the length. From my graph I have shown that my prediction was correct, as the line of best fit is a straight line proving that the resistance of the wire is proportional to the length of the wire. The length of the wire affects the resistance of the wire because if the number of atoms in the wire increases or decreases the length of the wire will increase or decrease in proportion.

The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a larger number of atoms there will be a larger number of collisions, which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased the number of atoms will also increase. From my graph it is easy to tell that the theory is correct and therefore my results reliable.

Evaluation.

In my graph I have shown one irregular point, this means that there must have been a slight error in my experiment. Although my graph is overall accurate and the results precise it is easy to see the irregular averages plotted because they do not all lie along the same line of best fit. The graph shows that my results are reliable as there is only one main irregular point. To improve the reliability of my results I could do more repeats in doing this my average would be more reliable.
I think one of the reasons why my experiment is quite accurate is because I tried to measure the wire as accurately as possible. As I increased the length of the adjustable wire, the wire became hotter and gave off heat. This could explain why the irregular result is at the lateral stage of my experiment. The metre rule was not taped onto the workbench this making it hard to measure accurately. As the metre rule was curved and worn down at the corners it was slightly hard to see where 0cm was.
During my experiment I have noticed that several improvements can be made to improve my investigation if I was to repeat it. The first of these improvements would be the circuit that I would use. To be more accurate with my results I would place the metre ruler directly under the wire, so therefore it would be measured easier and therefore making the lengths more precise. I would change the ammeter I used for a new digital one. I would connect a digital voltmeter to the wire that is being tested so that I will be measuring the voltage of just the wire being tested and not the wires of the main circuit as well. The next improvements I would make would be to use pointers instead of crocodile clips to attach to the wire; I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire. I would also use a newer metre rule. Instead of adjusting the length of one wire I would solder the wire to make my results more accurate.

My graph shows that my results are reliable as there is only one irregular point, to improve the reliability of my results, I could also have repeated the same lengths of wire more times. Although the wire is kept the same throughout, the thickness of it may vary by a small amount and maybe helping to cause the irregular results. Sometimes the ammeter flicked between a decimal point, I maybe could have thought it was the wrong number and therefore would have ended up with the wrong average resistance but using a digital ammeter would improve this. In the experiment, I did not control the room temperature but instead just assumed it was constant throughout my experiment; this could have made the wire get hotter and therefore making my experiment not as accurate. In future experiments I would control this variable factor and make it a constant factor. I would do this, as it would be an unfair test if there were two known variables.
As well as making these improvements, I could also expand on my investigation by testing the same wire but different widths of that wire and different materials of wire. I would do this if I had more time to complete it.

I think the circuit and method used was quite suitable although I would make the improvements above to improve my results. If I did this experiment again I would defiantly use top quality equipment, I would probably control the temperature and use pointers instead of crocodile clips. After changing those few things, there is not really much difference to how I would do the experiment again.