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# Relationship Between the Resistance of a Wire and its Length

Extracts from this document...

Introduction

The Relationship Between A Length of Wire and its Resistance

 The Relationship Between A Length of Wire and its Resistance Liam Owens 6/1/2011

Contents

Aim                                                                                        3

Background                                                                                3, 4 & 5

• What is resistance?
• What factors affect resistance?
• Relationship between current and voltage when a resistor follows ohms law.
• Relationship between current and voltage when a filament lamp is present

in a circuit.

Variables                                                                                6 & 7

Equipment                                                                                7, 8 & 9

Method                                                                                9 & 10

Pre-Tests                                                                                11 & 12

Bibliography                                                                                13

Aim

The aim of my experiment is to understand the affects upon the resistance of a piece of nichrome wire when varying the length at which electricity is transmitted through a circuit.

Background

What is Resistance?
Technically, resistance is defined as the ability of a substance to prevent or resist the flow of electrical current.
Electricity is conducted through a conductor, in this case nichrome wire, by means of free electrons. The number of free electrons depends on the material and freer electrons results in a better conductor. For example, a piece of metal such as gold would have more free electrons as the atoms do not hold on to their electrons very well in comparison to another conductor such as plastic which has less free electrons therefore, making it a worse conductor of electricity due to the higher level of resistance. The free electrons are given energy and as a result move and collide with neighboring free electrons. This happens across the length of the wire and thus electricity is conducted.
The smaller the cross-sectional area of the nichrome wire is e.g.

Middle

 Control Variable Why must it be controlled? How will it be controlled? Material We must use the same material due to the fact that various materials have different resistances. If I were to use a material with a high resistance then, one with a low resistance my results would become un-reliable. I will use a 26SWG Nichrome Wire (See justification in pre-tests section.) It will be attached to a 1 metre ruler. Temperature The variable power-pack will be turned off after each recording has been made (refer to method), this will allow the wire to cool down so it will not affect my data. Cross-Sectional Area As previously mentioned in the background (with figures 1 & 2) varying the cross sectional area of the wire (thickness) will affect the resistance and make the data collected less reliable. From the pre-tests and the fact that we did not have enough resources to vary the gauge of wire we will be keeping the Nichrome wire at 26SWGs. Current (0.5A) The current causes the wire to increase in temperature. Keeping the current low at 0.5A lowers the heating affect and ensures the resistance of the wire will not be affected. This will increase the reliability of my results. Through the use of a variable power-pack we can adjust the input of volts and maintain a constant current of 0.5 Amps for each test. Straightness of Wire The straightness of the wire affects the length of it. If a wire with a crocodile clip on it is connected at 20cm and the wire bends, the length and resistance of the wire changes. Therefore, we must keep the wire as straight as possible, that is why we are using a ruler and some sellotape. The wire chosen (26swg) can be easily straightened along a 1 metre ruler. For that reason, we will place the wire along the ruler and connect it to either end with the use of sellotape. This will lower the chance of the resistance being affected and thus, increasing the reliability of our results.

Equipment

 Equipment Name Justification for use Diagram Variable Power-Pack (0-12V) The use of a variable power pack allowed me or any member of my group to manually adjust the voltage input through the circuit in order to control and manipulate the number of amps being transmitted in our circuit, in our case it allowed us to keep the number of amps to 0.5 in order to make our experiment reproducible. Digital Ammeter Using a digital ammeter allowed for much more precise readings of the amps  present in the electric current with only a +/- 0.1 area for mistake in comparison to the traditional ammeter which has an area for error of +/- 0.5 as it requires the use of the naked-eye to record the readings. For that reason the digital ammeter was used in the experiment. Digital Volt Meter Digital voltmeters give a numerical display of voltage to 2 decimal places by use of an analog to digital converter, which lowers the margin of error to +/- 0.1 whereas, an analog voltmeter moves a pointer across a scale in proportion to the voltage of the circuit. This requires the use of the naked-eye and increases the margin of error to +/- 0.5. For that reason the digital volt meter was used in the experiment. 100cm Ruler with wire on The range of the length of wire was 25-95cm, the use of a 100cm ruler allowed us to easily place the wire straightly upon it and easily record the measurement of length in comparison to laying down four 30cm rulers which would have increased the error of margin in the reading of various lengths such as 35cm or 75cm. 26swg Nichrome Wire From the pre-tests we found that this wire could be easily straightened along the 1 meter ruler whereas the 36swg piece of wire could not which meant the resistance was not affected as there were next to no bends in the wire. Also, it was not as susceptible to heat as the 20swg wire which when heated would have caused the resistance to increase due to the more energy in the circuit, which would have increased the chances of collisions between free electrons and atoms. 2 x Crocodile Clips Crocodile clips allow us to connect the wires to the circuit (creating a complete circuit) in a safe manner which lowers the risk to the people involved in the experiment. 4 x Wires Using these in our experiment is essential. These allow us to connect each piece of equipment together for example; the voltmeter to thee variable power-pack.

Method

1. Clear your workspace, this will make your working area safe for you and your class mates and ensure that there are no accidents.
1. Place chairs/stools under desks.
2. Clear the desks of paper, books, bags etc. and simply have a pen and results table in order to record your results (following the steps below you will find out how to create a suitable results table).
1. Gather all the necessary equipment, as previously mentioned. The Equipment is necessary in order to undergo the experiment because if all equipment is not used or set up accordingly then the data will not be reproducible.
2. Set the equipment up as shown by the circuit diagram below, following this circuit diagram will increase the similarity to our experiment therefore, increasing the reliability of the results collected.
1. Now that the equipment is set up, ensure that the variable power-pack is turned off with the adjustable voltage dial is turned to ‘0’, this is to make sure that the wire does not heat up before acquiring data as the temperature will affect the resistance as previously mentioned in the ‘Background’ section of this document.
2. Create a results table with the following headings in a similar order. You should also include the suitable range of lengths at which you will be moving your crocodile clips in the appropriate column (wire length(cm)) For this experiment I chose to use the range of lengths; 25cm-95cm.
 Wire Length (cm) Current (A) Cross Sectional Area (swg) Voltage (V) Resistance (R = V/I) Test 1 Test 2 Test 3 Average

Conclusion

Finally, from the data gathered and the selection of resources used in this pre-test I can come to the conclusion that carrying out my final experiment in this manner would not be the best way to collect reproducible data, this is due to multiple reasons; one, there are simply not enough different pieces of wire with varying cross-sectional areas to carry out the experiment to satisfactory standard and two, the increments used are not very good for plotting a graph or conveying accurate results, the increments used in this pre-test were a follows – 4, 6, 10. This is not an even increase and would give me less confidence in my results when it came to plotting them on a graph.

Changing the Length of the Wire

 Length of Wire (cm) Current (A) Cross Sectional Area (SWG) Voltage (V) Average (V) Test 1 Test 2 Test 3 25 0.5 26 0.94 0.95 0.95 0.95 30 0.5 26 1.81 1.81 1.82 1.81 50 0.5 26 2.69 2.69 2.69 2.69 60 0.5 26 3.56 3.56 3.56 3.56 75 0.5 26 2.15 2.15 2.16 2.15 100 0.5 26 1.13 1.13 1.13 1.13

## Bibliography

 Part of Coursework Page No. URL What is Resistance 3 http://www.courseworkhelp.co.uk/GCSE/Science/15.htm “” “” http://www.freestudentstuff.co.uk/GCSE_Physics_Coursework_-_Resistance_of_a_Wire_Coursework.htm “” “” http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/electricity/resistancerev1.shtml Figure 1 3 Created by Liam Owens.Use of autoshapes in Microsoft Word 2007. Figure 2 3 “” Figure 3 4 http://www.gcse.com/energy/conduction2.htm Figure  4 4 http://www.pictutorials.com/Electronics_basics.htm Figure 5 4 http://www.antonine-education.co.uk/physics_as/module_3/Topic_2/topic_2.htm Figure 6 5 http://www.energysavers.gov/your_home/lighting_daylighting/index.cfm/mytopic=12120?print Figure 7 5 http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/electricityintheory/voltagecurrentresistancerev5.shtml

[1]http://www.courseworkhelp.co.uk/GCSE/Science/20.htm (factors which affect the resistance of a wire.)

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