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# Investigate how the length of a wire affects the wires resistance.

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Introduction

-  -        Daniel Sheedy 5S1 5JR

## Aim

The aim of this experiment is to investigate how the length of a wire affects the wires resistance.

## Background Information

Some variables that affect the resistance in a wire are:

• Length of the wire
• Thickness of the wire
• Temperature of the wire
• Voltage running through the wire
• Material of the wire

Of these variables, I will be investigating the length of the wire and how it affects the resistance. The other variables are going to be kept constant in the experiment to make sure that only length, of the wire is investigated and to make it a fair test.

The resistance (R) is measure in ohms (Ω), and is calculated by dividing the voltage (V) by the current (I):

V / I = R

Ohm’s law states that voltage and resistance are directly proportional, meaning that the doubling of one would result in the other being halved.  If the voltage was 50V and the current was 5A, then the resistance would be equal to 10Ω because:

V  /  I  =  R

50V / 5A = 10Ω

## Apparatus

In this experiment I will use:

• A number of wires
• An ammeter
• A voltmeter
• A metre stick
• A piece of copper wire
• Crocodile clips
• A power pack.

## Method

• A circuit will first be set up with a power pack, an ammeter in series and a voltmeter in parallel with the piece of wire that will be varied in length.
• As the power pack display is not at all accurate, a voltmeter will be connected directly with the power pack to make sure that it is set on 6 volts.
• Once the voltage is set the thinnest wire will be attached to a ruler so that it is easy to measure the length of wire being used.
• Two crocodile clips will then be attached onto the wire and into the circuit parallel with the voltmeter like in the diagram.
• The pack will then be turned on and the readings on both the ammeter and the voltmeter will be recorded.
• To see if the results are accurate, the resistance will then be calculated from the equation ‘R = V / I’.
• Readings will be taken with 100cm to 10cm wire pieces with 10cm intervals for a wide selection of wires to see patterns.
• For even more variety of readings a variable resistor could be implemented into the circuit and on each length of wire three readings could be taken for maximum resistance, minimum resistance and somewhere in between.
• We have decided to use the thickness of the wire as another factor, so on completion we will carry it out again with two more thicknesses, one wire of thickness gauge 36, one wire with thickness gauge 30 and the other with thickness gauge 28.

### Making the Investigation both Safe and Fair

• The power will not be left on too long to get the readings as temperature is also a factor that affects the resistance of a wire and leaving the wire would heat it up and therefore the results would not be accurate.
• The power supply will be set to 6 volts for all the wire lengths so that the only factor that is varying is the length of the wire.
• The same thickness wire will be used for each set of results, until the thickness is changed.
• Results will always be taken at 10 cm intervals on the wire from 100cm to 10cm.
• The voltmeter will always be in parallel with the piece of wire and the ammeter will remain in series with it throughout the investigation so that results can be taken.

Middle

4.37

0.86

5.08

5.1

20

High

1.17

0.35

3.34

20

Medium

1.81

0.53

3.42

20

Low

4

1.18

3.39

3.38

10

High

0.67

0.38

1.76

10

Medium

1.09

0.61

1.79

10

Low

3.16

1.79

1.77

1.77

###### Results for Wire with Standard Gauge 30 (0.31 mm diameter)
 Length of Wire (cm) Resistance of variable resistor (high/medium/low) Voltmeter Reading(V) Ammeter Reading (A) Resistance (V/I) (Ω) Average Resistance(Ω) 100 High 3.01 0.21 14.33 100 Medium 3.66 0.25 14.64 100 Low 5.05 0.34 14.85 14.61 90 High 2.8 0.21 13.33 90 Medium 3.56 0.27 13.19 90 Low 5.07 0.38 13.34 13.29 80 High 2.6 0.22 11.82 80 Medium 3.39 0.29 11.69 80 Low 4.49 0.42 11.88 11.80 70 High 2.42 0.23 10.52 70 Medium 3.26 0.31 10.52 70 Low 4.91 0.47 10.45 10.50 60 High 2.23 0.25 8.92 60 Medium 3.06 0.35 9 60 Low 0.53 0.53 9.02 8.98 50 High 1.99 0.26 7.65 50 Medium 2.83 0.37 7.65 50 Low 4.65 0.61 7.62 7.64 40 High 1.73 0.28 6.18 40 Medium 2.55 0.39 6.54 40 Low 4.52 0.7 6.46 6.39 30 High 1.43 0.3 4.77 30 Medium 2.25 0.48 4.69 30 Low 4.25 0.92 4.62 4.69 20 High 1.07 0.33 3.24 20 Medium 1.62 0.5 3.24 20 Low 3.84 1.19 3.23 3.24 10 High 0.74 0.35 2.11 10 Medium 1.10 0.57 1.93 10 Low 3.19 1.77 1.80 1.95
###### Results for Wire with Standard Gauge 30 (0.31 mm diameter)

Conclusion

If I was to repeat the experiment I do not think I could better the results much as I am very pleased with the accuracy. Next time though I could look at other factors like material.  This could be done much like the way that I carried out this experiment, the only difference being that I would not just use one material, I could use copper, nickel and chrome and find out which one offered the least resistance.  Temperature would be a hard factor to investigate as there is no way or really measuring the temperature of a wire with the equipment that is provided for us at school as a thermometer would be no good.   Again pressure could not really be completed within the school as we do not have a pressure cabinet and could not get pressure to desired levels.  Also we have to make check all the readings by hand as we have no way of connecting these up to a computer to check them automatically.  Also if I took more results next time, with not just three readings for each length, then the average would be that more accurate and so more reliable results would be recorded.

Overall though I definitely feel that the investigation was a complete success at investigating how both thickness and length of the wire attribute to the resistance that is offered.

Factors affecting the resistance of a wire

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