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Investigating how the length of wire affects its resistance

Extracts from this document...

Introduction

Investigating how the length of a wire affects its resistance

Aim:

To find out how changing the length of a wire will affect its resistance.

Introduction

Electricity is conducted through a conductor by means of free electrons. An electric current is made up of charged particles that flow called electrons. They move through a conductor, e.g. wire. The more free electrons in a conductor there is, the better it will conduct electricity as more mobile electrons mean more flow. Conductors of different materials have different amount of free electrons, therefore, some conductors conduct electricity better than others.

Resistance is what opposes the flow of current, (obstruction offered by the wire) and is measured in ohms, with the Greek symbol: Ω. Resistance makes it difficult for the flow of electrons through the conductor. It can be caused electrons colliding with atoms in a conductor, obstructing the flow. Electrons will also collide with each other if there is little free space in a conductor, and so resistance will increase.

Resistance can be affected by several different factors, such as light, temperature, width of wire, cross section area of wire, as well as the length of wire. In this experiment, I am going to investigate how the length of a wire will change its resistance. I will be using a range of wire lengths to test this.

Formula:

Resistance= Voltage/Current         R= V/I  

From the equation, I can obtain the resistance by measuring the voltage and current. I will use the reading for the current from the ammeter divided by the reading for the voltage from the voltmeter to calculate the resistance.  I can then know how I will be collecting my results.

Prediction:

I predict that the longer the length of wire is, the higher the resistance.

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Middle

0.25

1.4

5.6

45.0

0.2

1.3

6.5

50.0

0.2

1.4

7.0

For my preliminary experiment, I was experimenting on how I should set up for my real investigation. I adjusted different volts on the power pack. I initially used 1.5V, which gave me the results in the first table. It showed a clear trend, and there was no overflow of current, as my ammeter had no trouble displaying any readings. There was no problem with the readings on the voltmeter either, which stayed the same throughout. (Because of the low readings I only had to connect the wire to the 3V on the voltmeter)

A power of 3V went fine as well, although the wire did become quite hot when I used a power of 3V, and had even smoked a little when I used a wire length of 5 cm – my shortest length chosen.  There must have been a big flow of current there. The readings for the voltmeter however were fine.

I figured that I could not use a power of 4.5 V as the wire immediately began to smoke a lot, and was very hot when I turned the switch of the power pack on. I knew there was an overflow of current as my ammeter’s pointer went over the limit to a point where I could not obtain a reading. Therefore, I knew I must not use a voltage of 4.5 V or anything above.

To prevent difficulty like burning myself in my real experiment, I decided to then settle on a power supply voltage of 1.5 V, as the trend in the results is not significantly different to the one for 3V. With using a power supply of 3.0 V

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Conclusion

 Furthermore, I didn’t think about the temperature rising after current flowed through the wire when I did the experiment. I didn’t allow the wire to cool down for a certain amount of time. Sometimes I left the wire after I took the readings for a few minutes, whilst sometimes I carried on the experiment immediately after taking my readings. The temperature rises once current passes through it, which causes the atoms within the wire to vibrate. This increases the chance of electrons colliding with them, leading to a higher resistance. This would have caused inaccuracy in my results. Therefore, to prevent this if I do this investigation next time, I can time how long I leave the wire to cool by using a timer. This will make every trial I do have the same amount of time to cool down, meaning that the temperature of the wire would be more or less the same, thus making it a fair test.  

Finally, although I feel that I chose a decent range of readings to provide a clear pattern for me, I could try to use more readings in between the range I chose, for example, take a reading for every one centimetre, or increase the range I used, like 0cm to 100cm instead of just 0 to 50cm. More readings recorded means more points on the graph when I plot it, so the trend line drawn would be more accurate and reliable, and I will be able to spot any anomalies more easily. I could also do even more trials in the future to increase reliability of my results.

To take this investigation to a higher level, I could also try with different materials of wire to see if increasing the length of the wire does increase the resistance.  For this experiment, I had only used nichrome.

Thank you for reading this piece of coursework

Monica Liaw 10JG

...read more.

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Here's what a teacher thought of this essay

3 star(s)

Overall, this is a good report because it is very thorough in trying to analyse the results. Good comments have been made about controlling aspects of the experiment and no attempt has been made to ignore an anomalous result.

The addition of a graph would have improved this report. 3 stars

Marked by teacher Pete Golton 06/06/2013

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