After setting up the experiment like shown on the next page, in a series circuit. I set the power pack on 4 voltages, and I read the results of the current off the ammeter and the voltage off the voltmeter.
Resistance (Ohms) = Voltage (Volts)
Current (Amps)
This is the formula that I will use to work out the resistance of the circuit. Ohm’s law discovered that the amount of steady current through a large number of materials is directly proportional to the potential difference or voltage running across it.
Therefore if the voltage is adjusted it will not affect the resistance, as the current is always proportional to it, therefore meaning that any chance to the current will have no effect on out resistance or results. We will have to be careful that we don’t increase the voltage to the point it destroys the wire.
Below is a table of my results.
As you can see clearly the resistance increases as the number of resistance increases, these results are not immaculately correct due to minor errors, but close enough to the real results to depend on them.
Next I repeated the same experiment again but this time instead of using series circuits I used parallel circuits starting off with two resistors because you cannot have a parallel circuit with one resistor.
Here is a table of my results:
In these results you can see the resistance decreases as you increases the number of resistors in a parallel circuit, this is because the electrons have an easier way to flow through the current.
In terms of safety, the wire should not be touched at any one point of the experiment because it is not an insulated wire; therefore it is bound to be hot. Considering safety is essential whilst handling livewires and the voltage should be kept at a reasonable voltage, not only for safety reasons but also control the variables in the experiment.
To attain the most precise result, a number of factors need to be considered which enables us to achieve this. The variables are:
- Temperature
- Diameter of the wire
- Material of the wire
Diameter of the wire
By increasing the diameter of the wire we offer more space or routes for the electrons to pass through, therefore meaning fewer collisions with the other ions and less resistance. If the cross sectional area is smaller there will be greater resistance because there will be to more collisions between the ions as there are fewer routes for the electrons to pass through.
As the aim is to find out how the length of a wire affects the resistance we have to keep the rest of the variables constant throughout the wire during the experiment. To measure the length of the wire you use a micrometer, a sophisticated, very accurate device which measures the width of a wire to the nearest hundredth, allowing us a greater degree of preciseness.
Temperature
A solid is atoms which are attracted together tightly not allowing the atoms to move freely like they do in gases, but they can vibrate in a fixed position. When you increase the temperature you are heating up the particles, this causes them to vibrate faster because they are getting more energy. In a resistor it is even harder for electrons to pass along the resistance and the violent vibrating of the electrons, causing more collisions, therefore increasing resistance.
To try and reduce rapid change in temperature I have decided to use the constantan wire instead of the nichrome wire. This alloy’s resistance changes by less than 0.5% even when the temperature rises by a few hundred degrees proving it’s tight bonds of attraction between particles.
The material of the wire
I will be using a wire made up of Constantan for the experiment instead of Nichrome as metals all have different resistances as each has a different atomic structure. The wire used in the experiment has to be the same one throughout to keep it a fair test. Using different metals would produce anomalous results and our test would be inaccurate and unfair. By using only one material throughout out experiment we are attempting to keep our test fair. In addition to this we would have to consider the wire overheating due to the voltage being too high and this could lead to our resistance wire being set alight or melted and this may lead to our experiment being biased and unfair.
We must still monitor the temperature of our resistance wire as if we were to raise the voltage being fed into the circuit too much we risk over heating the wire and therefore burning or damaging it as well as affecting our results to a slight extent.
To give a fair set of results I have decided to take reading for 2 meters using 10 cm intervals. This gives us a good range of measurements with which we can produce an accurate graph and also means we can eliminate anomalous results.
Before we begin our experiment we will need to check all the equipment is working at optimum levels and make sure the ammeter and voltmeter we will be using have their pointers at exactly zero so our results are more accurate.
Step by step instructions:
- Set up experiment in this way
- Before starting the experiment, measure the width of the wire to check the constancy of the wire throughout (measured at 3.3mm)
- Set the voltage on the power pack to the required amount
- Switch on the power pack
- Take a reading of the voltage and current and record them in a table
- Switch off the power pack
- Move the crocodile clip along the wire 10 cm
- Switch the power pack on again and take another reading
- Repeat this until you reach 200 cm
Also the whole experiment has to be done twice to ensure a fairer set of results, which can be found by finding the average of the two results and then plotted into a graph
The width of the wire had to be measured at three places along the wire to see that the wire is constant throughout. It was measured at 3.3 mm.
As you can see the data is not very useful in a table form so I have decided to convert this information into a scatter graph, allowing us to analyze the information more clearly and to spot any anomalous results.
This graph allows us to analyse the information, and as you can see there is one anomalous result.
Conclusion
We can clearly see that increased voltage leads to increased number of collisions within the resistance wire therefore the resistance is increased. We can also see that the longer the resistance wire, the greater the resistance will be. This is due to the free moving electrons colliding with metal ions slowing them down and causing resistance, as our results show the longer the wire the more resistance.
I have used a great range with fair scale intervals as to be able to confidently say our results express a good example of what would happen accurately and means we can make our conclusions confidently.
Anomalous result
There is one anomalous result, in the last reading, which could have occurred for a number of reasons. This may be due to our crocodile clips not being precisely placed or minor changes in temperature or the width of wire that were not detected by our level of accuracy or preciseness i.e. Even the micrometer can only be accurate to a certain degree, hundredth of a millimeter and can be incorrect to a degree. The room must be made the right temperature, but room temperature cannot be controlled. This could not have been the reason because the last reading has a drastic change in resistance, and I am quite sure there were no major changes in temperature in the room whilst carrying out the experiment. There is even chance for human error as there is no perfect way of testing this. It may even be due to us rounding the results to two decimal places as we are changing our final results slightly making them not 100% accurate.
Conclusion
If I were to redo this experiment I would not round my results until after I found my average results, which I could then input into my graph because this can change the result slightly. This also shows that as our input variable becomes greater so does the output variable we are testing or the resistance however having rounded after producing both results would have given our results a greater degree of accuracy.
Also I would have used a digital resistance meter, which measures in Ohms, automatically using the formula to work it out.
Furthermore, I would have better-controlled conditions under which to complete the experiment therefore limiting the change in humidity as well as temperature, all variables that would affect the test.
Results
From our line of best fit we can see that our results support our predictions and that according to our graph the resistance increases. We can find the constant in the line by finding the gradient of the line:
Gradient= Y1 –Y2
X1-X2
= 190-100
11-6
= 90
5
= 18
The constant is 18, one ohm for every 20 centimeters added to the length. Furthermore our results graph shows all the points fit tightly along out line showing accuracy. As we can see a resistance wire of length twenty centimeters has a resistance of an ohm, 36cm being 2 ohms to prove this. This can be used to find the resistance and can be put in to a formula:
This can also be rearranged to find out the length when given the resistance.
We can see that these are vaguely accurate and can use this as a formula to find the any resistance of wire or the length required to create any resistance. Also this proves my points were accurate and this trend is supported by our research, hypothesis and preliminary work that supports the pattern formed by our results.
I can therefore conclude I have successfully and accurately investigated resistance and how it is affected by lengthening the length of a wire. I have done so with evidence and fair investigation and I believe have successfully completed the investigation to an extent backed up by preliminary work, scientific knowledge, hypotheses and prediction.
