Investigate the factors that effect the resistance of the wire.

My preliminary results: - These are my preliminary results for how the length of wire affects the resistance.

        

        

        I can see from my preliminary results that as the length of the wire increases, the amount of current, which gets through decreases, which means that the resistance increases. I can also see from my results that when the length of the wire has doubled the amount of current has almost halved.  

        These are my preliminary results for how the thickness of the wire affects the resistance.

        

        

I can see from these results that as the thickness of the wire increases the resistance increases because the number of particles that the current has to pass through increases, creating more resistance.

Prediction: - From my preliminary results I predict that as the length of wire increases the resistance will increase because when you increase the length of the wire there is more atoms for the current to pass through there for there is more resistance. I also think that when the length of wire has doubled the amount of current that gets through will have halved, I think this because it is shown in my preliminary results.

Apparatus: -  

• Multimeter (measures resistance to 2 d.p)
• Micrometer (measures c.s.a)
• Nichrome wire (26 swg)
• Crocodile clips
• Battery pack
• Wire

Method: - First of all I will measure out 5 lengths of wire, 30cm, 40cm, 50cm, 60cm and 70cm. I will do this by using a metre ruler. I will take 1 metre of wire to start with and measure the lengths of wire. I will cello tape the wire to the ruler to make sure that it is straight and that I’m getting the right amount of wire. I will then use a micrometer to make sure the wire is 26 swg. I will then set up my circuit and first put in 30 cm of wire to the circuit. I will do this buy putting crocodile clips on each end of the wire. I will then take the readings for the current after the wire and the voltage across the length of wire. I will then double check this by using a multimeter and measure the resistance across the piece of wire. I will repeat this three times. I will repeat the same method for all the other lengths of wire.

Fair test: - I will make it a fair test by using the same thickness of wire every time. I will use the same amount of voltage on the battery pack every time I take a reading. I will use the same equipment every time. I will also measure the thickness of the wire before every reading I take to make sure that it is always the same. I will make sure that the temperature of the wire is the same each time because as the temperature increases it causes the atoms to move around more, which creates more resistance as the moving atoms create a better barrier for the current.

Results

1st Attempt

2nd Attempt

3rd Attempt

Average

Analysis: - In my prediction I said that: I predict that as the length of wire increases so will the resistance. I have found that my results are actually incorrect because I haven’t calculated the resistance but I can analysis the affect the length of wire has on the current. These results are incorrect because the voltage shouldn’t be the same each time. The voltage should be measured across the wire so as the length increases the voltage should decrease. The resistance is then found from diving the voltage by the current. I can see from my results that my prediction was right because after the current has passed through the wire it decreases. This is more evident as the length of the wire increases because the current decreases as the wire increases. I can see from my average of results that when the length of the wire has doubled the current has almost halved because when the length of wire was 30 cm the current was 0.65 amps and when the length of wire was 60 cm the current was 0.32 amps, half of 0.65 is 0.325. I can see on my graph that my results a fairly accurate because three out of five of them touch the line of best fit and the forth point is 0.1 amps higher than the line of best fit. My reading for 30 cm is 1.1 amps higher than the line of best fit. From reading the line of best fit the reading for 30 cm should be 0.54 and I got the reading 0.65. The reading for the 70 cm of wire that I got was 0.26 but on my line of best fit it is 0.25. I can also see from my results the amount at which they decrease each time the length of the wire is increased is very similar. The difference between 30 cm of wire and 40 cm is 9 amps, the difference between 40 cm and 50 cm is 7 amps, the difference between 50 cm and 60 cm is 7 amps and the difference between 60 cm and 70 cm is 6 amps. This also shows that my results were fairly accurate and reliable.

Evaluation: - The first thing I would like to do is do my experiment again so that I can measure the resistance properly so that I can see if my prediction is really correct. I would measure the resistance properly by measuring the voltage across the wire and the diving the voltage by the current. I can see from my results that because all my readings do not touch the line of best fit they are not totally reliable. This may be because the temperature of the wire was different each time as I did not monitor the temperature or the length of the wire may not of been accurate because of the way the crocodile clips were placed. I would like to improve this by using pointers instead of crocodile clips; I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire. As well as making these modifications I would also improve my investigation by testing the same wire but different widths of wire. I would do this to expand on my investigation.