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Investigation into how the length of a piece of wire effects its resistance

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Introduction

Investigation into how the length of a piece of wire effects its resistance

Aim

Using different lengths of constantan wire, investigate how different lengths of wire effect its resistance.

Planning

My preliminary work before the actual experiment included going on a Science computer programme, on the topic resistance of a wire. In which I used to decide upon how I was going to do my experiment. I will take readings of lengths of wire from 0-70 cm and to make these readings accurate I will do them three times and take an average.

This is what the circuit will look like:

Prediction

I predict that the longer the length of the piece of wire, the more resistance it has. So, if you double the length of the wire, the resistance would be doubled aswell. When a metal wire is put into an electrical circuit, current from the battery makes the electrons flow through the wire. In doing so, they collide with the metal ions and this slows down the flow of electrons in the circuit. So, in a longer piece of wire you would expect more metal ions, with more metal ions there you would expect there to be more electrons colliding with them. Resistance is caused by electrons colliding

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Middle

2.9

2.7

70.0

3.4

3.5

3.4

3.4

3.2

Conclusion

The graph and results show me that the longer the wire, the more resistance it has which supports my prediction. In a longer piece of wire there would be more metal ions, and so more metal ions for electrons to collide with slowing their progress thus increasing resistance of the wire (resistance is a measure of how easy it is for the electrons to flow through the metal). Effectively, if you doubled the length of wire you would be doubling the resistance too. My results generally show this, but not as accurately. An example of the resistance being doubled when the length is doubled is when the length of wire was at 10.0 cm, the resistance of the wire was 0.5 Ohms. 10.0 cm doubled is 20.0 cm, and at 20.0 cm the resistance was 1.3 Ohms. 0.5 doubled is 1. It’s relatively accurate but not double exactly. I expected in my prediction that if you doubled the length of wire you would then double the resistance as it makes sense that if the wire were twice as long, the electrons would undergo twice as many collisions. If it’s twice as difficult to travel along the wire, we say that the longer wire has twice the resistance. My graph generally shows that length is proportional to the resistance, although it doesn’t clearly show this.

Evaluation

Overall, I think the experiment was done reasonably accurately.

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Conclusion

Evaluation

I found that I got much more accurate results in experiment 2 than I did in the first experiment. They were more reliable to make my overall conclusion. The results did prove my prediction. Although they aren’t completely accurate, as I think there is always some inaccuracy or error in results. In the second experiment a current was put through the wire, and this causes the temperature to rise, which will cause ions in the wire to vibrate, and so obstruct the flow of electrons, effectively causes the resistance to increase creating an error. However, when I was doing the experiment when taking the readings I turned the power pack off, so the temperature wouldn’t get to high.

        There are other limiting factors which could have affected my results which I have mentioned, like inaccurate meter ruler readings, temperature change or a unique error etc. But also when I used the variable resistor to keep the ammeter reading constant, it wasn’t always exactly the same as I couldn’t always get it to be the same reading every time.

        If I could do this experiment again I would use other variables aswell like temperature. How temperature might have an effect is that it provides metal ions with more kinetic energy, causing them to vibrate more, thus causing more electrons to collide with them. This causes the resistance to increase.

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