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# Investigating the factors affecting the current flowing through a wire.

Extracts from this document...

Introduction

Anna Belcher        Physics

## Background Knowledge

In this investigation I will be measuring the current flowing through a length of wire. A current is a flow of electric charge and will only flow when there is a complete circuit and a voltage. All substances are made of atoms which consist of a nucleus surrounded by moving electrons. In metals the outer electrons are ‘free’ and can be made to flow in one direction. If a potential difference is applied to a wire in a complete circuit a current will flow because the ‘free’ electrons will move. The electrons will move away from the negative side of the power supply and towards the positive side although the conventional current goes against the flow of electrons. The diagram below shows the electron flow.

There are two types of current that can flow around a circuit. Direct current is when the charge flows continuously in one direction. An alternating current is when the current flows alternately in both directions (positive to negative and vice versa). This can be shown on an oscilloscope as shown in the diagram below.

The current is a measure of the number of charges per second (Cs-1) and is measured in Amperes (A).

1A = 1Cs-1

An ammeter is used to measure the current and does this by measuring the number of charges passing a point per second. The equation to work out the current is shown below.

Current (A) = Charge (C)

Time (s)

## Charge flows from a point of high potential to a point of lower potential. Potential difference, which is measured in volts by a voltmeter, is the difference between them.

Middle

25.00

2.02

0.58

0.58

0.580

30.00

2.02

0.55

0.54

0.545

35.00

2.02

0.47

0.47

0.470

40.00

2.02

0.41

0.42

0.415

45.00

2.02

0.38

0.38

0.380

50.00

2.02

0.35

0.35

0.350

55.00

2.02

0.31

0.32

0.315

60.00

2.02

0.30

0.30

0.300

65.00

2.02

0.26

0.26

0.260

70.00

2.02

0.24

0.24

0.240

75.00

2.02

0.23

0.23

0.230

80.00

2.02

0.22

0.22

0.220

85.00

2.02

0.21

0.20

0.205

90.00

2.02

0.19

0.19

0.190

95.00

2.02

0.19

0.19

0.190

100.00

2.02

0.18

0.18

0.180

I have drawn a graph of the results as shown on the following pages, to aid me when choosing the most suitable wire. The results show that the values for the 0.38mm wire fluctuated more than those of the 0.27mm wire. I have therefore decided to use the 0.27mm wire as they did not fluctuate at all. This will give me more accurate results when carrying out the experiment. Also the graph of the 0.27mm wire is better as most points fit on the line whereas for the 0.38mm graph there are more points that do not fit. I have found that the range I have used is suitable. Measuring at 5cm intervals will give me more values and will make the graph more accurate and easier to plot. Also they will show a stronger relationship between current and length.

When carrying out preliminary work I have decided to use a power pack with a negligible internal resistance as this will make my results more accurate. The power pack that I have chosen to use has an adjustable voltage allowing me to set it to the voltage I want. I have decided to use a voltage of 2.02V as it gives a reliable and safe set of results. Anything smaller would give too low readings and anything higher would give to high readings. I had planned to use 2V however it was difficult to set the dial to exactly 2V and the nearest I could get was 2.02V.

## Fair Test

The experiment will be fair because I will only change the length of wire.

I will:

• Use the same voltage of 2.02V
• Use the same wire of thickness 0.27mm
• Connect the crocodile clips the same way each time
• Keep the material of wire the same (Nichrome)
• Keep the multimeter on the same range

Prediction

I think that as you increase the length of the wire the current will decrease. I think that the length of wire is inversely proportional to the current. This means that when the length doubles the current halves. This is because the longer the length of wire the more difficult it is for the current to flow. This is because the longer the length of wire has more material for the electrons to flow through meaning there are more ions to collide with. The more collisions there are the higher the resistance of the wire because the electrons loose more energy so slow down. Therefore the current decreases. This is shown in the diagram below.

Safety

Make sure that the circuit is set up correctly and that there is not a short circuit. Also do not use a high voltage, which could cause overheating. To prevent the wires overheating the circuit should only be connected up for a short amount of time. As well as this equipment must be checked to make sure it is working correctly. When working with the electrical equipment it is important to have dry hands.

Equipment

• Power pack
• Connecting wires
• Crocodile clips
• Metre ruler
• Wire of diameter 0.27mm
• Multimeter to measure resistance (Ω) and current (A)

Method

1.        Set up the apparatus as shown in the diagram above.

1. Set the power pack to 2.02V.
2. Measure the current through the 0.27mm wire at the lengths, 5cm, 10cm, 15cm, 20cm, 25cm, 30cm, 35cm, 40cm, 45cm, 50cm, 55cm, 60cm, 65cm, 70cm, 75cm, 80cm 85cm, 90cm, 95cm, and 100cm.
3. Record the results in a table.
4. Repeat steps 1-4 twice to make results more reliable.
5. Calculate the average current at each length.

Results

Diameter = 0.27mm

Voltage = 2.02V

 Current (A) Length (cm) Try 1 Try 2 Try 3 Average Current (A) 5.00 1.55 1.55 1.56 1.55 10.00 0.91 0.91 0.91 0.91 15.00 0.64 0.63 0.65 0.64 20.00 0.50 0.50 0.50 0.50 25.00 0.40 0.40 0.40 0.40 30.00 0.34 0.34 0.34 0.34 35.00 0.29 0.29 0.29 0.29 40.00 0.26 0.26 0.26 0.26 45.00 0.23 0.23 0.23 0.23 50.00 0.21 0.21 0.21 0.21 55.00 0.19 0.19 0.19 0.19 60.00 0.17 0.17 0.17 0.17 65.00 0.16 0.16 0.16 0.16 70.00 0.15 0.15 0.15 0.15 75.00 0.14 0.14 0.14 0.14 80.00 0.13 0.13 0.13 0.13 85.00 0.12 0.12 0.12 0.12 90.00 0.11 0.11 0.11 0.11 95.00 0.11 0.11 0.11 0.11 100.00 0.10 0.10 0.10 0.10

Conclusion

When carrying out the experiment I think that I took a sufficient number of readings in order to gain reliable results to support my conclusion. I took 20 readings and then carried out 2 repeats which means that a total of 60 readings were taken. This makes the results reliable. This is shown on the graph as all the points are on the line of best fit showing a very strong relationship between length and current. However more repeats could be carried out in order to further increase the reliability of the experiment.

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