Preliminary Work
For my preliminary work I am going to investigate how the current affects the potential difference across a filament bulb.
Results
After looking at these results I have found that the current and potential difference are not directly proportional to each other. This is because as the voltage increases the current increases at a different rate. This is due to the build up of heat in the bulb making the fixed particles more active setting up more collisions and a higher resistance. This has shown me that in my main investigation I will need to keep the current low in the circuit so that there is no build up of heat to affect the results.
I have chosen to investigate the length of the wire to see how it affects the resistance for my main investigation.
Apparatus
1 length of wire (constantan 0.31) over 1000mm
1 voltmeter
1 ammeter
1 rheostat (variable resister)
1 clamp stand
1 set of weights
2 crocodile clips
4 cells (batteries)
6 connecting wires
Aim
I want to find out the relationship between the length of the wire and the resistance of it.
Method
- Gather all equipment needed
- Place out in correct order and assemble circuit
- Connect the crocodile clips to the wire 200mm apart
- Set the rheostat so that the voltmeter reads 3 V.
- Read the ammeter and record the result.
- Reset the crocodile clips to 400mm apart
- Reset the rheostat so the voltmeter reads 3V
- Again record the result.
- Repeat this process 3 times for each length (200mm, 400mm, 600mm, 800mm, 1000mm)
Accuracy
To make sure that the experiment is accurate I need to insure that I read the ammeter and voltmeter exactly and make sure that the 2 crocodile clips are correctly placed at the stated distance.
Fair test
To keep the experiment fair I need to eliminate all the other variables apart from the one I am going to investigate. To do this I will ensure I use the same wire so that the material and the cross-sectional area are the same. Also I will carry out the experiment in approximately the same environment so moisture and temperature are the same each time to eliminate those factors affecting the results. Plus, I will only have the current flowing when I need to make readings so it would not heat up.
Safety
There is little danger to the people around and to me during this experiment due to the low voltage and current.
Hypothesis
I think that as the length of the wire increases so to will the resistance of it. I also predict that the rate at which the resistance of the wire increases will be directly proportional to the length. The graph to show this should therefore look something like this:
Reason:
This is because with electricity, the property that transforms electrical energy into heat energy, in opposing electrical current, is resistance. A property of the atoms of all conductors is that they have free electrons in the outer shell of their structure. All metals are conductors. Due to this fact the outer electrons are able to move about freely even in a solid. When there is a potential difference across a conductive material all of the free electrons arrange themselves in lines moving in the same direction. This forms an electrical current. Resistance is encountered when the charged particles that make up the current collide with other fixed particles in the material. As the resistance of a material increases so to must the force needed to push the same amount of current. In fact resistance, in ohms(R) is equal to the electromotive force or potential difference, in volts (V) divided by the current, in amperes (I) – Ohm’s law.
As the length of the wire is increased the number of collisions the current carrying charged particles make with fixed particles also increases and therefore the value for the resistance of the wire becomes higher.
Results
Here are the results I collected:
These are the basic results. Here are the results I need to get the relationship between the length of wire and the resistance.
And here is the graph
Analysis
In doing this experiment I have found that the results agree with my prediction almost perfectly. The prediction I made was that the longer the wire becomes the more resistance it would produce which would be calculated by using ohm’s law (R = V/I). This is a proven theory. I used it along with the collision theory to hypothesise that the longer the wire the more chances that the electrons had to collide with the static particles in the wire giving it a higher resistance.
The graph itself shows us that as the length of wire increases at consistent intervals the resistance of the wire increases proportionately. As I had previously predicted.
The line of best fit almost perfectly matches the points on the graph showing that they are all accurate and reliable. There are no anomalies. I produced this reliable set of results by taking into consideration all the points that I put across in the planning element of this investigation, such as, accuracy, method, fair test etc.
Using my results I can see that when you double the length of wire, give or take a few ohms, the resistance doubles also.
Evaluation
From the results that I have produced I can draw a general conclusion from them. This is in agreement with my hypothesis. The longer the wire became the resistance increased directly proportional to this.
The procedure I used to carry out the experiments was adequate as it gave a good set of results. The results obtained from the experiments were as accurate as I could achieve with the apparatus that I used. If I could do the experiment again I would make several changes to the apparatus used:
- Firstly I would use a more sensitive ammeter and voltmeter so that the reading I took could be more accurate. Also I would use digital ,metres so they would be easier to read. Therefore improving my results.
- Secondly I would work out the resistance of all the components in the circuit so that I could take them into consideration when doing calculations.
- Thirdly I would use better quality crocodile clips to make sure that the connection between them and the wire was strong. Also this would prevent them from slipping.
- I would keep a very high resistance in the circuit so to keep the current low.
After studying the results I have found that they are not suitable to form a solid conclusion on as they stand. Even though the experiment was taken out to a good standard there are still improvements that need to be made to get a reliable set of results so that I can form a conclusion. I would improve the experiments and apparatus in the ways stated above.
If I were to extend my investigations I would have to use a wider range of readings so I could gain enough information to put together a reliable and accurate set of results to produce a firm specific conclusion. Secondly I would use a better standard of equipment so that I will eliminate this factor that could affect my results. Also I could investigate other factors that will affect the resistance, such as temperature, diameter and the material of the wire.
