Balanced charges
The more collisions due to the moving charges, the slower the flow of current, higher resistance, because electric current is a flow of charges in metals or graphite, it’s negatively charged electrons that move.
How is measured: the resistance of a length of wire is calculated by measuring the current present in the circuit (in series) and voltage across it (in parallel). These measurements are then applied to this formula:
V=I ‘R
Where V = voltage, I = current and, R = Resistance
This also can be written this as
R = V
I
Ohms law: it is also important to know of Ohms law, which states that the current through a metallic conductor like a wire at a constant temperature is proportional to the potential difference-Voltage. Therefore V is constant to I. This can be meant the resistance of the wire is constant providing that the temperature also remains constant. Anther point is that the resistance of the wire increases as its temperature increases. This is because at a higher temperatures, the particles of the wire are moving around more quickly, therefore increasing the probability of the collisions with the free electrons.
A long wire has more resistance, than a short wire, one of the same materials, that’s the reason I’m going to use constantan wire, because it has higher resistance then copper and lower resistance then Nichrome wire.
The reason why I will use long thin wire is because as the electrons pass through the wire, they are hitting each other, they are slowing each other, because the wire is too thin for all the electrons to pass at a one time and also because is long, it takes longer time for the electrons to move around, and so the resistance becomes higher and the current will become lower, so its harder for the current to flow.
Method: my plan of method is that first I will set my experiment as shown below. To do this I will fix constantan wire to a metre long ruler. I will then clip one crocodile clip to the 0cm position on the ruler. The second crocodile clip will be on the end of the wire. I will then turn the power pack on, and will read off the ammeter and voltmeter and record it. After that I will turn the power pack off and the crocodile will move to the next position, which is 20cm. I will complete the experiment using these steps till I place the crocodile clips at 100cm, and then I will repeat the entire investigation two more times for accuracy.
Circuit diagrams: where this line indicates the resistance V the length of the wire.
Safety: while I’m doing this investigation I will consider the safety elements…….
- ensure that I don’t touch the wire while its hot
- I will also choose a low voltage so that it won’t over heat.
- Further more I will not try a length of less than 10cm, this is also helped me avoid over heating.
- I will also make sure that the area I’m doing my experiment is clean and no bags and anything else around.
- I will be wearing safety goggles to protect my eyes from the heat.
- I will also turn the power pack off each I’m doing the readings, because it will over heat.
Fair testing: to make it fair testing, I will consider the factors that affect the resistance of wire are constant. I will be using the same piece of wire through out the investigation, and the same equipment, as it will decrease the chance of errors in my result.
Key factors: the length of the wire and the area of the wire are the factors that will vary. The key factors that I will change as a result are the length of the wire. The dependent variable is the resistance. However I will keep the material of the wire the same, as a control experiment, because my investigation is looking at how the length of a wire affects its resistance.
Preliminary result: Before I done this result table, there was a preliminary investigation that I did. That investigation was wrong because when I was doing the investigation I changed the length of the wire, not the current, and when I did my graph I got lots of anomalies. I think I got lots of anomalies because maybe the length of the wire’s measurements wasn’t correct. Its possible that the length was short at 90cm, causing it o lower resistance, and at 100cm is possible that it was longer , causing it higher resistance. But when I did repeat my investigation I made sure that the wire was pulled tight against the metre rule. I also did not disconnect the circuit properly, there were some errors in my method, and as I was reading the current and voltage I did not turn the power pack off which made the wire heated up. Furthermore I started with a high voltage.
Result tables:
After I repeated the test three times for accuracy, I then add the length of wire and divide it by three to get the average result; I add the resistance and divide it by three to get the average result as well, and these are the result for length of wire V resistance of wire.
Average results:
I also did an average result for current V voltage
Average result:
Conclusion: having performed the investigation, I have drawn the following conclusions: As the length of wire increases so does the resistance of wire, which makes my prediction correct. I can say this because my graph shows that it gives a reasonably straight line, showing a positive correlation between the length of wire and the resistance of the wire. It also shows that the resistance is directly proportional to the length of the wire, and the line of best fit passes through the origin. If you increase the length the resistance increases. The theory behind these is as the length of wire increases, the resistance increases, because resistance is caused by electrons bumping into ions. If the length of wire Increases, the electrons bump into the ions more so the resistance increases causing. The reason why electrons bump into ions are because they loose energy in the form of heat and, in turn its speed is reduced, but wire heats up, so the number of times that electrons bump to ions is on average that will than be directly proportional to the length of the wire , so will the resistance. If the resistance is directly proportional to the length of the wire, we can then say that R=V
Evaluation: over all my result is quite accurate due to the fact that nearly the entire points bar sits on the line of best fit except at 100cm which is 18.2 ohms. The reason is because at 90cm the resistance was 17.7 ohms, but at 100cm it goes up high at 18.2 ohms. I think that happened because I didn’t turn the power pack off when I was reading the result for 90cm, and it got hot, so when I changed the crocodiles to 100cm, it was already hot and the voltage and current was high. If I could improve this investigation, I would let the wire cool down completely, so the temperature wasn’t high enough for that measurement, causing the resistance to be high. But after I done some research I found out that metal alloy like constantan is not affected by temperature. Therefor in this experiment ohms law does not apply. The investigation would also be more accurate if I used digital ammeter or sensors. My method was accurate because I repeated the investigation each time I got it wrong improving it more and making sure that I don’t make the same mistake.
