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# Preliminary work using a length of Resistance Wire.

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Introduction

Preliminary work using a length of Resistance Wire (constantan)

Introduction

In this investigation I will be trying to find out the resistance of a piece of constantan wire.  I know that according to ohms law, the p.d is proportional to the current so if the p.d doubles so will the current. Through past experiments I know how to work out resistance, to work it out I use this formula

Where the resistance is R, the p.d is V and the current is C, from this you can work out the resistance of any circuit.

Aim of the Preliminary

The aim of this preliminary work involves making decisions about the length and thickness of the wire, which will be suitable for the main investigation

The preliminary work will only involve one type of wire – constantan because there are available 5 different thicknesses of this wire and very few of other wires in the department.

The 5 different thicknesses of wire I am testing are

1. 36 SWG (very thin)
1. 34 SWG
1. 30 SWG
1. 28 SWG
1. 26 SWG (very thick)

I tested all the wires at 3 volts, first I set up the equipment as shown below (Diagram) and then recording the results on the table below

Results

 SWG Type Length of wire in mm Voltage(volts) Current(a) 36 500 3 0.52 34 500 3 0.62 30 500 3 0.81 28 500 3 1.73 26 500 3 2.23 36 400 3 0.63 34 400 3 0.89 30 400 3 1.43 28 400 3 2.13 26 400 3 2.52 36 300 3 0.62 34 300 3 1.34 30 300 3 1.72 28 300 3 2.31 26 300 3 2.92

Conclusion

As you can see from the results the wire of SWG 30 has a good range of current for the 3 lengths chooses; 0.81A to 1.72A.

Middle

If a wire is longer, the moving electrons have further to go, so there is more chance of an electron colliding with an atom. Increasing the length of a wire increases its resistance.

If a wire is longer, the moving electrons have further to go, so there is more chance of an electron colliding with an atom. Increasing the length of a wire increases its resistance.

Due to all these factors this is why I have thought that the smaller the wire the smaller the resistance

Testable hypothesis

along with my prediction I will also have a testable hypothesis to see if I can make a prediction that I can test it, for my hypothesis I think that if I double the length of wire the resistance will also double I think this because of ohms law, ohm’s law states that the voltage across a component is directly proportional to the current through it provided its temperature does not change. This les to an equation know as ohm’s law equation :         so if V is set fixed at 3 Volts then if the current increases due to the length shorting then it follows that resistance must be less, also if the current doubles as the result of halving the length then the resistance must be half its original value.

Further Science to explain this

Electrons have to flow through the wire.

Conclusion

To make this experiment more reliable we could use a different piece of wire for each length then if the temperature increases which opposes the flow of the electrons it would not effect the next reading at a different length. To make the results more accurate I could use a digital ammeter and digital volt meter which are accurate to 0.01A and 0.01V, if I was using theses also they cannot be misread like the normal ammeter and voltmeter as it is a digital display.

To extent this investigation we could take more readings for example every 5cm in stead of 10cm and increase the maximum wire length to 200cm, also do more repeats, 5 times and not 3. Other experiments that could be done is to change the voltage and see how this affects the current and resistance. Also we could include temperature readings to see how the temperature is affected by the current voltage, and resistance. This would involve using temperature sensor touching the wire; the temperature sensor could be plugged into a data logger that will collect the readings

The original method is reliable and gave me some useful results. It is reliable because I have tried it 3 times before to find out about the current through a resistor, a bulb and a diode and each time my results agreed with the notes in the revision guide (Lonsdale Science Revision Guides, The Essentials of AQA Science: The Tested Modules, The Terminal Examination and The Additional Modules

Daniel Wheatley

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