Investigating how the length of a wire affects the resistance of a wire.

Prediction:

I predict that the length does affect the resistance of a wire, the longer the piece of a wire, the more resistance it will have. That is because in the longer wire there the more energy is needed to move electrons down the wire and therefore more pressure is needed to move those electrons so we have to increase the voltage to get the same current.

Also there will be more atoms for the electrons to collide with, and so the resistance would be greater. The relationship between the length of the wire and the resistance should be directly proportional. This is because in a wire twice the length of another wire there would be double the amount of atoms causing the resistance.

Variables:

Independent variable        : Length of wire.

Dependant variable        : Resistance of wire.

Control variables                : Type of wire, Thickness of wire, Room temperature (about 22 C), Person doing the experiment, Same day, Same equipment or apparatus used.

Trial Experiment:

We will be using:

1. 2 Batteries, 1.5 volts each / Power Pack.
2. An ammeter which measures to 0.01 amps.
3. A voltmeter which measures to 0.01 volts.
4. 36 S.W.G. Nichrome wire.
5. Crocodile clips.

1. Set apparatus as shown in the diagram.
2. Fix one meter of the wire on a meter ruler.

1. Fix the first crocodile clip to the wire at the 0cm on the meter ruler.
2. Fix the second crocodile clip to the relevant position on the meter ruler depending on the requirement length of wire.
3. Turn the power supply on(or connect the batteries)
4. Voltage and current are then read off the ammeter and voltmeter and recorded.
5. Power supply is turned off (or batteries disconnected).
6. The second crocodile clip is moved tot he next position.

1. The above steps are completed for length and then the entire investigation is repeated for accuracy.

Results of Trial Experiment:

As we carried out the experiment, we noticed that the wire heated up during the experiment which meant that this was not a fair test a fair test because resistance varies with temperature, and we want only one variable to affect the experiment which is the length of the wire.

To assure that a fair test is done therefore we decided to add a variable resistor in the circuit. The variable resistor keeps the current constant, and since that we have a constant current therefore we will have a constant temperature.

Safety:

In order to perform a safe experiment, a low voltage of 3V was chosen so that overheating was avoided. Also lengths less than 10cm were not tried, which also helped to avoid overheating.

Method:

After setting the apparatus as shown in the diagram and adding in the variable resistor to set the experiment to a constant current to cause the temperature to be also constant, follow those steps:

1. Set the first crocodile clip lead to the 0cm position on the meter ruler.
2. Fix the second crocodile clip lead on the 10cm position on the meter ruler.
3. Turn on power supply or connect batteries.
4. Set the current to 0.02 amps to get a constant temperature.
5. Read off voltmeter reading.
6. Calculate resistance (resistance=voltage/current), and record results
7. Turn off power supply or disconnect batteries.
8. Move the second crocodile clip from 10cm to 20cm and repeat experiment again. After finishing each of these experiments move the crocodile clip 10cms up till you get to 80cm.
9. Make sure you repeat the whole experiment till you think that your results are reliable enough, and then make an average of all your results.

Results:

Average results:

Analysis:

My results and graph show that the length of the wire is directly proportional to its resistance also gets doubled. And as the length trebles, the resistance also trebles.

When we had a length of 10cm we got a resistance of 20.5 ohms, when that was doubled to 20cm; the resistance got also doubled to 33.5 ohms. And when the 20cm were doubled to 80cm its resistance got doubled from 52.50 ohms to 98.75 ohms (if the numbers weren’t exactly doubled, then the given numbers are very close to the exact numbers).

My prediction was corrected; an increase in length resulted in an increase in resistance. Not only that, the length is directly proportional to its resistance, therefore as the length doubled, the resistance also doubles and as it trebled, the resistance also trebled and so on.

This is because as you increase the length of the constant wire, more energy is needed to move electrons, therefore more pressure is needed to move electrons, and therefore more pressure is needed to push the charges or the electrons along the wire. Therefore the voltage must be increased, and as you increase the voltage, resistance also increases.

Evaluation:

I think that I carried out the method accurately, so I got accurate results. I think that two repeats and an average result were sufficient. I don’t think that I had any incorrect results and my results and graph show that.

I had an accurate method. I avoided the inaccuracy of the wires by using only one wire, which was 36 S.W.G. Nichrome wire, that I was sure that didn’t have any other variables affect the results like thickness. To insure that I had the right lengths, I adjusted the crocodile clips, one on the 0cm position, and the other on whatever length I am experimenting e.g. on the 10cm or the 20cm position.

I did that because I felt that some of the wires were short, long, thick, or thin. This would affect the experiment by using more than one variable and it would also affect my results negatively.

I think that I had reliable results because both of the sets of results that I got had nearly the same results and my results and graphs show that.

I don’t think I had a problem with the accuracy of the experiment because I used accurate equipment that measured to the nearest 0.01 units.

I could have improved the experiment by using a bigger range of lengths, and I could have done more sets of results to make my results more accurate. Or even I could change the variable from the length of the wire, to the thickness of a wire or even changing the material of the wire. But I have to consider that I have to keep all the other variables constant of I am changing one of them. i.e., if I am changing the thickness of the wire, I have to keep the other two variables constant. So the length has to be the same all through the experiment, and also I have to use the same kind of wire all over the experiment.