I am going to calculate the resistance in a constantan wire using ohms law.
I will do my experiment as follows; I will take a power pack and the first thing I did was tried the voltage on 12, the highest, but I found out this was too extreme as it overheated the wire and it could have been a danger to myself. This measurement was unreadable on the ammeter and voltmeter, as it went off the measurement scale. I changed it to the lowest setting, 2v, and this worked fine.
For a fair test I would keep the same voltage from the mains, the same ruler and the same apparatus. I will only change the length of constantan wire for every 10cm. I will not change the wire thickness because I don’t have any more wire, but I could predict that the thicker the wire the higher the resistance because it has a larger surface area.
I also did some research on constantan wire and I found out that constantan is a flexible alloy of supposedly 60% copper and 40% nickel.
For my prediction, I should expect to see the resistance level rise, as the length of the constantan wire gets longer. I think this because the more wire there is for the electricity to pass through the more ions it has to pass. This causes the resistance to increase because there will be more collisions.
Here are my predictions
- The longer the wire, the higher the resistance. This is because the longer the wire, the more times the free electrons will collide with other free ions in the wire. Therefore, more energy is going to be lost in these collisions (as heat).
- Furthermore, doubling the length of the wire will result in double the resistance. This is because by doubling the length of the wire is also doubling the collisions that will occur, so it must also double the amount of energy lost in these collisions.
Method
The following circuit was constructed to perform the investigation:
Apparatus: voltmeter, ammeter, power pack, constantan wire, ruler (0-100cm) and five wires with crocodile clips.
Method
1. Constantan wire is fixed to a metre rule.
2. The first crocodile clip is clipped into place at the 0cm on the metre ruler.
3. The second crocodile clip is placed in the relevant position depending on the required length of wire. The lengths in cm I am using are 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100.
4. The power supply is turned on. The voltage and current are then read off the ammeter and voltmeter, and recorded.
5. The power supply is then turned off and the second crocodile clip is moved to the next position.
The above steps are completed for each length and then the entire investigation is repeated three times for accuracy.
Obtaining Evidence
Results
The resistance was calculated using ohm’s law voltage divided by current.
I did this twice and then calculated an average table for accuracy.
Analysis
My Conclusions
Having finished this experiment, the following conclusions were made.
- As predicted, an increase in length resulted in an increased resistance. This can be clearly said for both tests. The increased length of wire means a larger surface area thus meaning more collisions can take place along the wire.
- The length of the wire is shown to be proportional to the resistance - double the length and the resistance doubles.
Evaluation
I think that overall my experiment went quite well and that the results were fairly accurate, but in order to make them even more accurate I could have repeated the experiment a few more times to be able to get a more accurate resistance, if I had had time. Sometimes the current or voltage would read incorrectly, this glitch might have been caused by a fault with the ammeter or voltmeter or by the overheating of the wire. The other, smaller anomalies could have been made by bends in the wire making the length slightly longer than what was wanted. These things may have caused errors in my results, but I think that generally my results are accurate enough to support my conclusion.
I think that my equipment was fairly appropriate for the task and my method was straightforward to follow.
To extend this experiment I could change the thickness and lengths of wire to prove the conclusions I have shown are correct. Changing the thickness of the wire would back up my theory that increased surface area increases collisions. Changing the length, i.e. shortening the wire, would also back up this theory, as there would be a smaller surface area and fewer collisions.
I could also try using wires of different metals, to see if that would affect the outcome of the resistance.
