Some metals have less resistance than others. Wires are always made out of copper because copper has a low resistance and therefore it is a good conductor.
Resistance opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. The circuit itself can resist the flow of particles if the wires are either very thin or very long.
The material and cross sectional area of the wire is constant throughout the experiment. Therefore it is clear from the formula that the resistance should be directly proportional to the length
Variable
In this experiment I will only change one factor, the length of the wire. This should affect the resistance of the wire. This is also the key variable.
Here are the 4 factors, which will affect my experiment:
Temperature - constant
Length of wire - Variable
Cross Section – constant
Metal – constant
Safety
What I am planning to do is a safe procedure. I have pointed out some key safety precautions: when we are using the electricity we have to be careful at all times not to shock or burn our selves, due to the current getting to hot. We must make sure that all the lab rules are followed and that we don’t use faulty equipment. I will carry out the experiment in the laboratory in a safe environment. Mention lab rules, more safety on electricity, wire getting to hot- risk of burn
Fair test
In this experiment we are only changing one factor – the length of the wire, the factors that we are going to keep the same are as follows, to keep the experiment as a fair test:
We must keep the surrounding room temperature the same or the particles in the wire will move faster (if the temperature is increased) and this will therefore have an effect on the resistance. Therefore the room temperature must be kept constant to make it a fair test.
The cross sectional area of the wire must be kept constant throughout as well. As the cross sectional area is a factor that effects the resistance.
The material of the wire must also be kept the same as different materials have different conductivity. The last two factors will be kept the same by using the same wire all of the way through the experiment.
The current that we pass through the wire is to be kept the same, also. If this is changed the temperature of the wire might change in a way that is not constant, making the results more confusing. How r u goin to keep the variables constant, safety in both experiments.
The above factors are needed to keep the experiment as a fair test.
Prediction
I think that as the length of the wire increases so to will the resistance of it. I also believe that the rate at which the resistance of the wire increases will be directly proportional to the length. Relate it back to scientific knowledge, why? Prediction in both experiments
Preliminary Work
I carried out a preliminary experiment to prepare for the final investigation. These were my results:
1st Reading
2nd Reading
Average Resistance
I discovered by my preliminary work that my prediction was correct. That the rate at which the resistance of the wire increases was directly proportional to the length of the constantan wire.
Hypothesis
Now I can predict from my preliminary work that as the length of the wire increases the resistance will also increase.
Method
Now I can create my method as I have conducted my preliminary experiment. I will take 5 readings from different sets of wires: 20cm, 40cm, 60cm, 80cm and 100cm and I feel I need to repeat the experiment twice to obtain exact results. To ensure my results are accurate I will repeat the experiment 2 times, taking 5 readings each time, and then I will find the average reading.
I will make basic circuit which I have illustrated in the diagram below:
Apparatus
These are the apparatus I will be needing:-
- 5 different sets of Constantan wire.
- Power pack
- Connecting wires
- Crocodile clips
- Voltmeter
- Ammeter
7) Rheostat
Results
1st Reading
2nd Reading
Average Resistance
I took two readings then I found the average reading. I believe I took a sufficient amount of results which will be reliable. The rate, at which the resistance of the wire increases was directly proportional to the length of the constantan wire, was what I again discovered from my final results.
To portray my results I will use the form of two bar charts to portray the relationship between the length of the wire and the voltage and current. Then I will draw a graph to show how the electrical resistance of the constantan wire changed in the relationship to its length.
Conclusion
I have come to the conclusion that the rate, at which the resistance of the wire increases was directly proportional to the length of the constantan wire.
If I come back to my scientific knowledge it stated that:
“Resistance opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. The circuit itself can resist the flow of particles if the wires are either very thin or very long.”
In my case the wire was very long therefore the circuit can resist the flow of particles which increased the resistance. Also in my scientific knowledge it stated:
“The unit of resistance is Ohms. The higher the resistance, the lower the current. If there is high resistance, to get the same current a higher voltage will be needed to provide an extra push for the electricity.”
This is also true as the current decreased when the resistance increased however the voltage was sustained and increased to provide the extra push for electricity.
My results support the original prediction made as I said: “I also believe that the rate at which the resistance of the wire increases will be directly proportional to the length.” And this is what my results portrayed.
Evaluation
I thought this experiment went quite well however I did have some problems with measuring the wire, and it getting hot when it was a short piece only.
The results and evidence that I have collected were quite accurate, however when a graph was drawn there were some points which were anomalies, but they were very close and followed a stable pattern along the line I drew. There were two results that I thought was out of pattern - was the value of resistance for 100cm wire: as my graph 2 portrayed that there was an anomaly with measuring the current therefore it affected the resistance, which produced an overall anomaly. The anomalies are identified on the
graphs that I have drawn. One anomaly was for measuring the current and the other was for the resistance graph. The first anomaly effected the other.
The apparatus I used did allow me to obtain the necessary degree of accuracy this is portrayed through my graphs. I believe the equipment was sufficient enough for me to carry out a successful experiment.
There were no problems with the procedures used but I could of improved my results by using a pointer instead of crocodile clips, pointers have a smaller surface area so will not affect the resistance to much, and give more accurate measurements. I would also try different voltages instead of 2V I would use 4V or 6V. And I would investigate the resistance of wires of different materials. I would also try investigating into different variables such as temperature, thickness of wire and type of wire used.
The results I achieved have successfully answered and investigated what I has intended to do at the beginning of the investigation. I took sufficient results to be able to draw a graph successfully which was sufficient and accurate enough. I could not draw a line of best fit as it seemed easier to draw a line graph to make it easier to identify anomalies.
I think that the method of measuring the wires was insufficient as it wasn’t very accurate, which could have effected the results. It was hard to measure the wire as it was at times curled up at the ends so I would choose to try to measure the wires more accurately in future by possibly measuring in millimeters.
To avoid any anomalies I would have had to measure the current from the rheostat more accurately. As my first anomaly, inaccurately measuring the current, affected my second anomaly which was the resistance for 100cm.
In future I would have to measure everything (wire, voltmeter and rheostat) to a certain degree of accuracy.
The improvements and further work I would do is to use pointers instead of crocodile clips, investigate with different voltages, and investigate with different variables such as temperature, thickness of wire and type of wire used. These improvements and further work could have provided additional evidence for the conclusion and it could have extended the investigation.
References
This is where I obtained some of my information which has helped me in my planning:
- GCSE EDEXCEL REVISION BOOK - LONSDALE
-
GCSE REVISION GUIDE – CGP
