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# Investigating how thickness and length affect the resistance of particular wires.

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Introduction

Investigating how thickness and length affect the resistance of particular wires

Equipment

The equipment that I will need to perform this experiment will be:-

• Battery pack
• 5 Wires
• A volt meter
• An ammeter ( 0-15)
• Crocodile clips
• Ruler
• Nickel chrome wire

Method

The first thing that needs priority when setting up a circuit is safety. I will handle everything with dry hands and take extra care so that I don’t short circuit the experiment. The experiments will be investigating the relationship between the thickness of the wire and the length of the wire. I will connect up a circuit like shown above, the power supply coming from a power pack. A volt meter and an ammeter will be placed in series and the wire which I will be investigating, so will be changing, will run in parallel to the ammeter. The set up of the circuit will tell me exactly how much current is going through the circuit. With this information I can put the figures into an equation that will work out how much resistance that particular wire has. I chose to investigate length and thickness as they are both continuous as opposed to the type of wire which is -----. Once I have got the readings from the ammeter and voltmeter I can put the data into this equation.

Resistance (r) = voltage (v)

Current (i)

I am going to measure the amount of current which passes through six different thicknesses of nickel chrome.

Middle

Thickness

(SWG)

Thickness

(mm)

calculation

Average

(A)

20

0.90

(1.8 + 1.85 + 1.9) ÷ 3

1.85

22

0.71

(1.45 + 1.5 + 1.5) ÷ 3

1.48

24

0.56

(0.15 + 0.15 + 0.2) ÷ 3

1.17

26

0.45

(0.85 + 0.9 + 0.9) ÷ 3

0.88

28

0.37

(0.65 + 0.65 + 0.65) ÷ 3

0.65

30

0.31

(0.4 + 0.4 + 0.4) ÷ 3

0.4

To work out the resistance of each wire I am going to put in the average readings into the equation. The voltage was kept constant at 3volts so I’m going to divide 3 by each of the average readings.

 Thickness(SWG) Thickness(mm) Calculation Resistance(  ) 1dp 20 0.90 3 ÷ 1.85 1.6 22 0.71 3 ÷ 1.48 2 24 0.56 3 ÷ 1.17 2.6 26 0.45 3 ÷ 0.88 3.4 28 0.37 3 ÷ 0.65 4.6 30 0.31 3 ÷ 0.4 7.5

I have plotted a scatter graph of the results to see if there is a pattern. I am hoping that it will be inversely proportional where as the thickness in mm increases the resistance will decreases.

Length

 Length (cm) Result 1, amps (A) Result 2,amps (A) Result 3,amps (A) 10 1.5 1.5 1.5 20 0.85 0.85 0.85 30 0.6 0.6 0.6 40 0.45 0.45 0.45 50 0.4 0.4 0.4 60 0.3 0.3 0.3 70 0.25 0.25 0.25 80 0.225 0.225 0.225 90 0.2 0.2 0.2 100 0.15 0.15 0.15

Conclusion

The reason for the resistance to increases as the length increased is because the electrons have to travel further meaning there will be a lot more points where the electrons will be colliding with the ions. I can see that there the results increase at a curtain rate. I have worked out that the average resistance increase is about 1.8 ohms. When working out this calculation I dismissed the reading for 50cm as it was an anomaly.

Evaluation

I personally think that the experiment went very well. The experiment proved what I originally thought would happen. The resistance increased as the thickness of the wire decreased. My results were very good as I seem not to have any anomilious data and they all support my prediction. I think that my results are quite accurate; the only thing that could have been inaccurate was the length of the wire as we had to keep changing the wires over. Even though I made sure I was as accurate as possible the results could have been 6.6% inaccurate due to the plus or minus 1 factor in the measuring.

If I had more time to do the experiment I would have done some more repeat readings as there wasn’t enough time to do more than that three sets of results for each thickness of wire. I probably would change the length of wire is I got the chance to redo the experiment. I would make the wire longer, about 50cm or even 100cm. This will reduce the amount of possible inaccuracy as it would go down to 1% or 2%.

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