# Resistance. I plan to keep this a fair test. The only variable will be the length of wire. The wires length will go up in 10s from 10cm to 100cm.

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Aim: To see how the length of a wire affects its resistance

Preliminary Work

Diagram

For the preliminary work we set up the above circuit. The circuit contained a power-pack, wire, a voltmeter and an ammeter. We changed the length of the wire and also changed the current to work out which current would work the best.

We got the following results:

Length of Wire (cm) | Current (A) | PD (V) | Resistance (Ω) | Notes |

10cm | 1A | 1.4V | 1.4Ω | - |

50cm | 1A | 7.5V | 7.5Ω | Wire getting warm |

100cm | 1A | 14.5V | 14.5Ω | Very hot |

10cm | 0.5A | 1V | 2Ω | O.K |

50cm | 0.5A | 3.6V | 7.2Ω | O.K |

100cm | 0.5A | 6.5V | 13.0Ω | - |

50cm | 3A | Off scale | - | Burnt out |

Plan

I plan to keep this a fair test. The only variable will be the length of wire. The wires length will go up in 10’s from 10cm to 100cm. From the preliminary work we found out that the best current to use was around 0.5A so I will use a current of 0.6A because 0.5 is hard to read. The current will remain exactly the same throughout the investigation. Another thing which will not be changed during the investigation is the wires thickness and type of wire. The wire I will be using is Nichrome at 30SWG. Temperature will remain at room temperature. I will measure the potential difference (V) and calculate the resistance using ohms law.

R (Ω) = Voltage (V)

Current (A)

Method

I will set up the circuit which contains a power-pack using a current of 0.6A, the variable, which is the length of wire, an ammeter and also a voltmeter. To begin I will use a wire with the length of 10cm. The power-pack will then be switched on and the voltmeter will be read. Then the resistance can be measured. I will repeat this in cm’s going up in 10’s up to 100cm.

Prediction

I predict that the shorter the wire the less resistance there is and the longer the wire the more resistance there will be. The outer most electrons from each atom can escape from the atom and can whiz around between the atoms. When there is a long wire there are also lots of atoms. Because there are so many atoms and electrons it makes it hard for the electrons to whiz around without colliding with the atoms and transferring energy to them. The resistance is from the electrons having to force past atoms, much like walking down a busy corridor and colliding with people as you walk along. When you have a shorter wire, there are less atoms and electrons, making it easier for electrons to flow free.

ResultsNichrome 30 SWG Wire

Length (cm) | Current (A) | PD (V) | Resistance (Ω) |

10cm | 0.6A | 1.4V | 2.3Ω |

20cm | 0.6A | 1.75V | 2.9Ω |

30cm | 0.6A | 2.55V | 4.25Ω |

40cm | 0.6A | 3.4V | 5.6Ω |

50cm | 0.6A | 4.5V | 7.5Ω |

60cm | 0.6A | 5.2V | 8.6Ω |

70cm | 0.6A | 6V | 10Ω |

80cm | 0.6A | 6.5V | 10.8Ω |

90cm | 0.6A | 7.6V | 12.6Ω |

100cm | 0.6A | 8.0V | 13.3Ω |

Nichrome 30 SWG Wire [Repeat]

Length (cm) | Current (A) | PD (V) | Resistance (Ω) |

10cm | 0.6A | 0.6V | 1Ω |

20cm | 0.6A | 1.5V | 2.5Ω |

30cm | 0.6A | 1.7V | 2.8Ω |

40cm | 0.6A | 3V | 5Ω |

50cm | 0.6A | 3.4V | 6.2Ω |

60cm | 0.6A | 5V | 8.3Ω |

70cm | 0.6A | 5.7V | 9.5Ω |

80cm | 0.6A | 6.5V | 10.8Ω |

90cm | 0.6A | 7.6V | 12.6Ω |

100cm | 0.6A | 8.5V | 14.2Ω |

We then decided to see what the results would be with a thinner wire. So we used 38 SWG Nichrome

Length (cm) | Current (A) | PD (V) | Resistance (Ω) |

10cm | 0.6A | 5.0V | 8.3Ω |

20cm | 0.6A | 7.0V | 11.6Ω |

30cm | 0.6A | 12V | 20Ω |

40cm | 0.6A | 15V | 25Ω |

50cm | 0.6A | Off scale | - |

60cm | 0.6A | - | - |

70cm | 0.6A | - | - |

80cm | 0.6A | - | - |

90cm | 0.6A | - | - |

100cm | 0.6A | - | - |

We then decided to change the wire. 38SWG Constantin Wire

Length (cm) | Current (A) | PD (V) | Resistance(Ω) |

10cm | 0.6A | 1V | 1.6Ω |

20cm | 0.6A | 1.8V | 3Ω |

30cm | 0.6A | 2.9V | 4.8Ω |

40cm | 0.6A | 3.5V | 5.8Ω |

50cm | 0.6A | 5.6V | 9.3Ω |

60cm | 0.6A | 5.8V | 9.6Ω |

70cm | 0.6A | 6.5V | 10.8Ω |

80cm | 0.6A | - | - |

90cm | 0.6A | - | - |

100cm | 0.6A | - | - |

Conclusion

As the length of wire increased the resistance also increased. My prediction was correct.[See prediction] With a 10cm piece of 30SWG Nichrome wire the resistance was on average 1.65Ω and a piece of 100cm 30SWG Nichrome had an average of 13.75Ω. The resistance went up.

This is because the outer most electrons from each atom can escape from the atom and whiz around between the atoms. When there is a long wire there are also lots of atoms. Because there are so many atoms and electrons it makes it hard for the electrons to whiz around without colliding with the atoms and transferring energy to them. The resistance is from the electrons having to force past atoms, much like walking down a busy corridor without colliding with people as you walk along. When you have a shorter wire, there are less atoms and electrons, making it easier to flow free.

Evaluation

I believe that my results were accurate. This is because the results were repeated again to check the accuracy. Between the two results they both gave around the same results.

In the results there was only one anomaly. This was using 30cm length Nichrome wire 30SWG. I believe that the anomaly could have occurred for a number of reasons; there may have been a loose connection. The Ammeter or Voltmeter may have been misread or the length of wire may have been read wrong. Temperature could have also affected the result. When the wire gets hot resistance increases. Particles vibrate so it’s harder for electrons to pass through.

I think that I could have repeated my results again to make the results even more accurate. Although after repeating it twice there was only one anomaly.

To improve my method to get more accurate results I could have made sure the wire was exactly cut to the right amount. The voltmeter and ammeter could have been digital instead of analogue. The temperature could also have been kept the same throughout using controlled temperature, the power-packs could also have been digital. I could have also used the Wheatstone bridge method.

Another aspect of the investigation that could be investigated is if the width of the wire affects resistance. I managed to investigate this and found out that it did affect the resistance. The thinner wire had the most resistance with the readings going off the scale at 50cm using 0.6amps.

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