4) With your fingers, move them across the wire to straighten out the creases that could stop it being measured accurately, thus preventing accurate results.
5) To make sure that fair readings are taken measurements should be taken for 0cm, 20cm, 40cm, 60cm, 80cm, and 100cm, which will be done by moving the connector leads up the constantan wire in 20cm gaps.
6) The readings should then be taken for the resistance, and repeated two more times to get an accurate average.
7) The results should then be recorded in a table.
(If I weren’t to have a multi-meter I’d have to note the current and voltage and use the following to find the resistance:
Resistance (Ohms) = Voltage (volts, V) x Current (amps, I)
Scientific Knowledge:
An Atom is made up of a nucleus surrounded by shells of electrons. These electrons move around more freely in metals. A power supply or battery provides electromotive force (EMF), which repels the negatively charged electrons apart from the negative terminal and towards the positive. The positively charged nucleuses stay where they are, although, they are still being attracted to the negative terminal.
It can be said that the thinner the wire, the less spaces it has, as there are less nuclei, which greatly increases the probability of a collision or resistance because there are fewer spaces to go through. The more spaces a wire has and the thicker it is, the more gaps there are available and the greater number of electrons that can flow with fewer collisions with less resistance. In general, thinner wires have more resistance than thicker wires, which allows bigger current flows. (Sources: text books and my own knowledge)
The said above is why I’m keeping the thickness of my wire the same, so to make it a fair test, but I’ll be changing the length of my wire. I will also keep the material of the wire the same as the resistance will be affected by different metals.
As a wire gets hotter, the resistance increases, which can be explained through the activity of the atoms. When the wire heats up either because of large current flow through a small wire or a high temperature, the resistance increases simply because the nuclei vibrate faster. This means the spaces between neighboring nuclei are decreased and the resistance increases, and oppositely, when a wire is cooled, resistance decreases as there is more gaps between the nuclei as they are vibrating slower.
The resistance and length of a wire are directly proportional to eachother- R L, which is why I predict that as the length of a wire doubles, so does the resistance.
Prediction:
The length of the wire makes a difference, considering the longer the wire, the more the electrons squash together so that they are capable of passing through the wire. I predict that as you double the length of a wire, its resistance also doubles, because it’s the collisions between ions and electrons that triggers resistance, therefore the longer the wire, the more positive ions, so there are more collisions, thus the resistance increases.
Experiment work:
Results from the practical:
From my preliminary results I realised for my next test I’d have to place the masking tape on the tips of the ruler, although not at the very ends (0cm and 100cm), as the masking tape prevented the connector leads conducting with the wire during the preliminary run, as you can see I got 0Ω for 100cm, which was obviously incorrect due to the masking tape
The accuracy of our experiment was –0.4 Ω. For every result, we had to take 0.4 Ω away, and then record the outcome in our table because when we first connected the connector leads, the number that appeared on the multi-meter was 0.4, although it was meant to be 0, therefore meaning for every result to be fair I’d have to subtract 0.4.
Analysis
My line graph is showing a positive correlation. From what I can see there are two anomalous results, however they are not major.
My graph proves that if the length of the wire is increased accurately then the resistance is also increased. Therefore the length seems to be proportional to the resistance. For example when the length is 20cm the resistance is 1.2Ω, when the length is doubled to 40cm the resistance is also almost doubled to 2.2 Ω. The line of best fit is the straight line that’s running through the origin and is as near to all the points as possible, it showed me how resistance and length (relatively) increase proportionally to each other. My graph shows that as the length is increased, the resistance also increases, which supports my prediction, however, my graph doesn’t prove that as you double the length of a wire, its resistance also doubles, because when you go from 20cm to 40cm, the resistance doesn’t double as it should. It’s likely that my graph wasn’t directly proportional due to inaccuracy in the experiment.
In a longer length of wire, it is more likely for the electron to bump into a nucleus. If a wire of 3cm has a resistance of 3 ohm, then in a 6cm wire, it would be expected to have a resistance of 6 ohms. This is because when the length is doubled, there are twice as many odds for the electrons to bump into a nucleus. Considering the resistance is how the material resists the flow of electrons, a double increase in length means that there is twice as many nuclei to bump into, which also means the resistance would increase the same.
Evaluation
In general I think this investigation has went reasonably well. There were 2 anomalous results that slightly stood out on the graph which shows that the experiment wasn’t done to the highest accuracy possible, however the two anomalies almost fitted the trend, showing that I performed the task accurately enough. This was because I used the right equipment and made sure that I took my results as accurately as I could at the time, which is shown by my readings for the three runs, as they are all very alike which shows that the data is dependable. To make my experiment even more reliable I could have used a more stable wire which would have made my measurements more accurate, because the wire may have slackened during the experiment. Therefore to improve my experiment next time I would test the rigidity of the wire throughout my experiment instead at just the beginning. I could have also used another type of wire that had a different thickness, which would consequently get similar results but would progress my experiment.
