# --- PHYSICS INVESTIGATION ---

Extracts from this document...

Introduction

--- PHYSICS INVESTIGATION ---

FACTORS WHICH AFFECT THE RESTISTANCE OF A WIRE

AIM: The aim of the investigation is to investigate the factors that affect the resistance of a wire.

Resistance is affected by certain factors. The four main factors which affect resistance are:

- Temperature
- Length
- Thickness
- Materials.

These must be kept constant throughout the experiment except the length of the wire. These CONTROLLED VARIABLES (except LENGTH) are as explained:

- TEMPERATURE: affects resistance as when the temperature of a metal increases the resistance of the metal increases and the current decreases. The reason for this is because as the temperature increases the atoms of the metal tend to vibrate more vigoursly each time as of the increase in energy. This in turn makes it more difficult for the electrons to move across the wire as they collide with the atoms of the metal on the way to the positive end of the wire, therefore increasing the amount of collisions meaning there is/would be more resistance. However, keeping the temperature constant throughout the experiment could prove fairly difficult as the temperature could easily increase or decrease, unless you have the correct apparatus to keep the temperature constant or complete the experiment on the same day at room temperature. It is essential to use a low voltage as it will mean a low current which will not heat up the wires. If a high voltage was used then the energy would be in the form of heat which will affect the resistances and therefore make the experiment unfair. Out of the two types of wires provided (Nichrome and Constantan), nichrome would be unreliable as it is affected by temperature, which therefore will affect the resistance, where as constantan wouldn’t and instead would provide you with better results.

- LENGTH

Middle

2v

10

0.64

0.3

0.5

0.73

0.3

0.4

*0.66

0.4

0.6

0.50

2v

20

0.43

0.4

0.9

0.45

0.4

0.9

0.52

0.6

1.2

1.00

2v

30

0.38

0.5

1.3

0.32

0.4

1.3

0.39

0.6

1.5

1.37

2v

40

0.28

0.5

1.8

0.26

0.5

2.0

0.32

0.6

1.9

1.90

0.37

2v

50

0.23

0.5

2.2

0.20

0.5

2.5

0.28

0.6

2.1

2.27

2v

60

0.18

0.5

2.2

0.19

0.5

2.6

0.24

0.6

2.5

2.43

5v

70

0.97

3.1

3.2

0.98

3.2

3.3

0.98

3.3

3.4

3.30

5v

80

0.86

3.2

3.7

0.88

3.2

3.6

0.89

3.4

3.8

3.70

5v

90

0.77

3.2

4.2

0.79

3.2

4.1

0.80

3.4

4.3

4.20

0.37

5v

100

0.71

3.2

4.5

0.72

3.2

4.4

0.73

3.4

4.7

4.53

5v

110

0.65

3.2

4.9

0.66

3.2

4.8

0.67

3.5

5.2

4.97

5v

120

0.60

3.2

5.3

0.60

3.3

5.5

0.62

3.5

5.6

5.47

5v

130

0.56

3.4

6.1

0.56

3.3

5.9

0.58

3.5

6.0

6.00

5v

140

0.52

3.4

6.3

0.53

3.3

6.3

0.54

3.6

6.7

6.43

0.37

5v

150

0.49

3.4

6.9

0.49

3.4

6.9

0.51

3.6

7.1

6.97

5v

160

0.46

3.4

7.4

0.47

3.4

7.2

0.48

3.6

7.5

7.37

5v

170

0.44

3.4

7.7

0.44

3.4

7.7

0.46

3.6

7.8

7.73

5v

180

0.41

3.3

8.0

0.42

3.4

8.1

0.44

3.6

8.2

8.10

5v

190

0.39

3.3

8.5

0.40

3.4

8.5

0.41

3.6

8.8

8.60

0.37

5v

200

0.37

3.3

8.9

0.38

3.4

8.9

0.40

3.6

9.0

8.93

KEY

W – Width of Wire (mm) * Repeated – Was 0.88A before repeating anomalous

P – Power in volts (v) result & 0.66A after repeating the experiment at

L – Length (cm) 10cm for experiment 3.

I – Current in amps (A)

V – Voltage (v)

R – Resistance (Ω)

AVR – Average Resistance (Ω)

All the readings made were taken at 10cm interval across the 2m length of constantan wire, and I have recorded all my outcomes from the experiment in the results table above. I have labelled the table with the correct units/ produced a key. Using this data I have produced a graph showing the relationship between the average resistance and the length of the wire.

I have used the apparatus appropriately and safely in order to produce reliable results as well as following a structured reliable method to help produce these results and to make sure the experiment goes according to plan.

To get accurate and reliable results the experiment was repeated twice more to see if any of the results on the previous experiments contained anomalous, unreliable outcomes. For example the second experiment contain an anomalous results (as shown on table) which differed completely compare to the outcomes of experiments one and three. To be able to plot the graph and compare the resistance against the length of the constantan wire the average resistance was calculated. This data in turn was transferred to produce the graph.

When analysing the graph I would be able to see if there are any outstanding anomalous results/outcomes and if so I could/can use scientific explanations/reasoning on why they occurred.

ANALYSIS:

Conclusion

e.g.

Using the same formula or equation I have worked out the resistance of the other lengths and have placed this on a table shown on the following page which I will be comparing using the results calculated using the formula/equation:- Resistance (R) = Voltage (V) / Current (I), which are also shown on the table in red.

Length of wire (m) | Resistance (Ω) | Resistance (Ω) | Avr Resistance (Ω) |

0.10 | 0.4557248942 x 10-6 | 0.46 x 10-6 | 0.50 |

0.20 | 0.9114497885 x 10-6 | 0.91 x 10-6 | 1.00 |

0.30 | 1.367174683 x 10-6 | 1.37 x 10-6 | 1.37 |

0.40 | 1.822899577 x 10-6 | 1.82 x 10-6 | 1.90 |

0.50 | 2.278624471 x 10-6 | 2.28 x 10-6 | 2.27 |

0.60 | 2.734349365 x 10-6 | 2.73 x 10-6 | 2.43 |

0.70 | 3.19007426 x 10-6 | 3.19 x 10-6 | 3.30 |

0.80 | 3.645799154 x 10-6 | 3.65 x 10-6 | 3.70 |

0.90 | 4.101524048 x 10-6 | 4.10 x 10-6 | 4.20 |

1.00 | 4.557248942 x 10-6 | 4.56 x 10-6 | 4.53 |

1.10 | 5.012973837 x 10-6 | 5.01 x 10-6 | 4.97 |

1.20 | 5.468698731 x 10-6 | 5.47 x 10-6 | 5.47 |

1.30 | 5.924423625 x 10-6 | 5.92 x 10-6 | 6.00 |

1.40 | 6.380148519 x 10-6 | 6.38 x 10-6 | 6.43 |

1.50 | 6.835873414 x 10-6 | 6.84 x 10-6 | 6.97 |

1.60 | 7.291598308 x 10-6 | 7.29 x 10-6 | 7.37 |

1.70 | 7.747323202 x 10-6 | 7.75 x 10-6 | 7.73 |

1.80 | 8.203048096 x 10-6 | 8.20 x 10-6 | 8.10 |

1.90 | 8.658772991 x 10-6 | 8.66 x 10-6 | 8.60 |

2.00 | 9.114497885 x 10-6 | 9.11 x 10-6 | 8.93 |

Comparing the two sets of Resistances (the resistance and average resistance), you can see that the resistance at each of the length intervals differ whether it’s a big difference or small. This in turn shows that the equation for resistivity produces more accurate and reliable results, which is because there is no need to calculate the average resistance but instead feed the lengths and area of cross- section into the equation and calculates the resistance as an whole, precisely and accurately.

The graph below shows my prediction of how a graph showing that current (I) is proportional to voltage (V) would look like.

To calculate the gradient of the graph showing Current (I) is proportional to voltage (v) the formula/equation above should be used in further experiments and in order to do this the average current and voltage need to be calculated. Producing the graph and calculating the gradient will in turn determine if my prediction to what the graph would look like is correct. This could be taken forward and shown in further/future experiments.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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