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# Resistance coursework

Extracts from this document...

Introduction

How the resistance of a wire is affected by the length of the wire

Resistance(Ω) is a measurement of how much current can flow through a circuit. The unit of resistance is the Ohm. High R → Low current. And Low R → High Current.

Current (I) is a measure of the flow of electrons (e-). The unit of Current is the Amp (A). Current is measured using an ammeter.

Voltage (V) is a measurement of energy transferred. The unit of voltage is the Volt (V). The Voltage is measured using a voltmeter.

Ohms Law - George Ohm discovered that the Voltage across a component in a circuit is directly proportional the current (I) passing through that component providing the temperature of the component remains constant. This can be put as, V/I is constant. This constant is known as the resistance which is now measured in Ohms.

V/I = R or

V - Volts
I - Current
R – resistance

This is as long as the temperature is constant.

Metals

Metals are good conductors of electricity and heat because they have unfilled space in the valence energy band.

Conduction is the movement of electrically charged particles through an electrical conductor. The movement of charge constitutes an electric current.

Middle

1.26

0.22

5.73

700

1.25

0.25

5

600

1.19

0.28

4.25

500

1.2

0.34

3.53

400

1.16

0.41

2.83

300

1.13

0.52

2.17

200

1.06

0.73

1.45

100

0.93

1.3

0.72

Constantan 26 SWG

 Length (mm) Voltage (V) Current (A) Resistance (Ω) 1000 1.22 0.4 3.05 900 1.20 0.44 2.73 800 1.15 0.47 2.45 700 1.10 0.51 2.14 600 1.06 0.59 1.80 500 1.03 0.69 1.49 400 1.01 0.83 1.22 300 0.97 1.08 0.90 200 0.85 1.39 0.61 100 0.62 2.14 0.29

Justification (for preliminary)

Overall I decided to use Constantan 26 SWG because it offered a lot more resistance than copper which barely gave any. I chose to use the multimeter rather than the analogue ammeter and voltmeter as I found the multimeter easiest to read and more accurate as it fluctuated less, this will immensely improve my data. After my preliminary I decided to set my power pack to 3 volts as any higher than this caused the wire to heat therefore creating more resistance. And any lower would not have enough push to the electrons round the wire. The variables I will control are Amount of volts being delivered and the temperature of the wire. To make sure the wire was not hot when I turned it on I left the power pack off for 30 seconds after each reading, also I made sure I left the power supply on for the shortest amount of time possible. I controlled these variables to ensure it was a fair test.

The Main One

Equipment:

• Power Pack- (I used 3 volts) I used a power pack because it is more reliable than batteries and I can choose how many volts I want to use
• Copper Leads – Very little resistance
• Nichrome Wire
• Constantan Wire
• 2x Crocodile clips
• 2 x multimeters – One to measure the Current and the other to measure the voltage.

Method:

.

After gathering all my equipment I started making my circuit. First of all I connected the power pack to the mains, I then set it to 3 volts as that’s what I decided to use after my preliminary. After that I connected one copper lead to the DC (direct current) hole and connected the other end to the multimeter (ammeter). Next I connected a lead into the other hole in the ammeter and plugged the other side into a crocodile clip. I will then attach another lead into the lead plugged into the crocodile clip the other end into the voltmeter. I will then connect another lead to the DC output on the power pack this lead will then be connected to a crocodile clip with another lead plugged into that lead going into the voltmeter. I will then cello tape a wire to the ruler and connect the crocodile clip to both ends. Then I will turn on my power pack and record the results from my ammeter and voltmeter (multimeter) and then I will move the crocodile clip down the ruler by 100mm each time and then record the results. I will be repeating this for as many times needed to get reliable results e.g. if the results have a big range I will keep repeating it until it has a smaller range. I will make a table for each time I repeat it. And then make an overall average from my RAW data.

Results:

1st

Constantan SWG 26

Multi meter

3 Volts

 Length (mm) Voltage (V) Current (A) Resistance (Ω) 1000 1.19 0.39 3.05 900 1.17 0.43 2.72 800 1.16 0.48 2.42 700 1.12 0.52 2.15 600 1.08 0.59 1.83 500 1.08 0.72 1.50 400 1.01 0.84 1.20 300 0.93 1.03 0.90 200 0.82 1.37 0.60 100 0.67 2.24 0.28

Conclusion

Evaluation:

My results were exceptionally reliable as the range between each result was minuscule; most results only had 0.01/0.02mm difference. Because of this we didn’t have to do too many repeats, but we still repeated it 4 times to ensure our data was precise and reliable. There were NO outliers in our data, so we were able to use all of our data. Also my pre-tests helped me to adapt my experiment and make sure it was accurate and a fair test. I used the same number of d.p in my results to make it clear and accurate. As you can see in my graph for average the error/range bars are extremely small, this means my results were extremely reliable. Therefore I think I had high levels of precision while doing it. I don’t think my data had any weaknesses because it was tremendously reliable, but there are still a few things I could improve such as measuring the wire, I could have fully made sure there was no bends or crinkles on the wire. Another thing I could do to improve my data is by leaving the power pack of for longer after I used it so the wire had more time to cool down.

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