# Investigating the effect of 'length' on the resistance of a wire

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Introduction

NAME:

Physics coursework

Investigating the effect of length on the 7

~PLAN~

For this investigation, I first decided to list all the factors which I think may affect the resistance of a wire and the reason for their importance. These factors are:

- Material of the wire – If the wire is a conductor, more electric current will flow therefore the resistance would decrease, copper is an example of a good conductor. Insulators do not allow the flow of electric current which means the resistance will be at its peak.
- The length of the wire – The longer the conductor, the further the electrons have to travel, the more likely they are to have collisions with metal ions and so the greater the resistance.
- The temperature of the wire & surroundings – As the temperature increases the metal ions vibrate more (kinetic theory) leading to more frequent collisions with the electrons and therefore provide greater resistance to the flow of electrons.

From the factors above, I chose the length of the wire to investigate.

I obtained most of my information from:

- “KEY SCIENCE for GCSE Physics” by Jim Breithaupt.
- “Collins Total Revision GCSE Science” by Chris Sunley & Mike Smith.
- “CGP GCSE Double Science Higher Physics” by Richard Parsons.
- “Letts AS Physics” by Graham Booth.
- Class work that I have done throughout my GCSE course.
- The internet (educational websites, e.g. www.gcsephysics.com & www.physlink.com). I also used “www.goodfellow.com”.

I used the sources above to choose the suitable equipment needed for my investigation including the type (material) of wire and its appropriate diameter. I also used them to write about the background information or scientific knowledge.

Aim:

My aim is to investigate ‘how the length of a wire will affect its resistance’.

Middle

Apparatus:

- Two (2) Batteries (each 1.5 V).
- Crocodile clips.
- Connecting Wires.
- A voltmeter.
- An ammeter.
- A wooden plank slightly longer than 1 metre.
- One metre ruler.
- A constantan wire which has a length of at least 1.15m and a diameter of 0.11mm.
- Two screws.
- Two nails.
- A micrometer.
- A calculator to calculate the resistance and the mean average for each length.

Diagram:

Planned Method:

The ruler will be put in the centre of the wooden plank and it would be nailed into it by two nails. After the ruler has been anchored on the plank of wood, two screws will be screwed into the wooden plank at either ends of the ruler, the screws will also be touching the ruler. The wire chosen for the experiment will be tied around the screws more than once, to ensure that the wire is taut and has no kinks to give better accuracy in the results. The voltmeter will obviously be connected around the wire in parallel to the circuit and the ammeter will be connected in series to the circuit. I will allow the wire to cool for 30 seconds between each two readings. I will use a micrometer to measure the diameter of the wire. I will be taking results every 10cm between the 10cm and 90cm, this range and the intervals were chosen as I found it most appropriate from my preliminary test.

- I will set-up the equipment as shown in the diagram above.
- I will start off by putting the crocodile clips on 10cm of the wire.
- I will read and record (in a table) the readings of the ammeter for that particular length.
- I will read and record (in the same table but a different column) the readings of the voltmeter for that particular length.
- I will repeat the same again, but will move the crocodile clips 10cm (0.1m) up the wire.
- I will keep adding 10 cm to the length and then reading and recording the results until the length is 90cm.
- I will repeat all of this twice to obtain average results.
- At the end I will calculate resistance by dividing the voltage by the current (R=V/I) and putting the answer in a third column for the resistance of that particular length.
- I will finally average the resistance for each length. I will do this by adding the 1st and 2nd resistance calculations and then dividing total by two. So for the length of 50cm I will have two resistance calculations and a third which is an average of the two.

~Obtaining Evidence~

I set up the experiment using the equipment I mentioned in the planning section except that I also included a thermometer in the apparatus:

- Two (2) Batteries (each 1.5 V).
- Crocodile clips.
- Connecting Wires.
- An analogue voltmeter.
- An analogue ammeter.
- A wooden plank slightly longer than 1 metre.
- One metre ruler.
- A constantan wire which has a length of at least 1.15m and a diameter of 0.11mm.
- Two screws.
- Two nails.
- A micrometer (0-25mm).
- A calculator to calculate the resistance and the mean average for each length.
- Thermometer (accuracy of up to 1 d.p).

Conclusion

My results would have been much more accurate if I had taken these factors into consideration, they would also be better if I make the appropriate improvements.

Further investigation:

To extend the work that I have done, I would like to investigate the effect of varying the cross-sectional area of a wire on resistance. I can do this by using wires of different diameters but of the same material. My original method (with the improvements above) would remain the same but without changing the length.

The greater the cross-sectional area of the conductor, the more electrons available to carry the charge along the conductor’s length and due to more free space the collisions will be reduced and so the resistance is lower. I predict that the cross-sectional area would be inversely proportional to the resistance, so if I double the cross-sectional area the resistance would half. I predict that the graph of cross sectional area against resistance would be like the sketch below:

Resistance (Ω)

Cross-sectional area (mm2)

Ten (10) different diameters of the same wire would be appropriate; I would record the three (3) sets of results in 3 different tables similar to the one below:

Cross-sectional area (mm2) | Voltage (V) | Current (A) | Resistance (Ω) R=V/I |

0.1 | 2 | 0.1 | |

0.2 | 2 | 0.11 | |

0.3 | 2 | 0.13 | |

0.4 | 2 | 0.17 | |

0.5 | 2 | ||

0.6 | |||

0.7 | |||

0.8 | |||

0.9 | |||

1.0 |

Finally I would calculate the resistance by adding the three different resistance calculations and the dividing by 3:

R1+R2+R3/3=Average Resistance

I would lay out the average resistance results in a table similar to the one below:

Cross-sectional area (mm2) | Average Resistance (Ω) |

0.1 | |

0.2 | |

0.3 | |

0.4 | |

0.5 | |

0.6 | |

0.7 | |

0.8 | |

0.9 | |

1.0 |

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