# Investigate one of the factors effecting current flowing through a wire.

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Introduction

Investigation – Factors effecting current flowing through a wire

Aim - To investigate one of the factors effecting current flowing through a wire.

Factors –

- Length – The length of a wire affects the resistance. The longer the wire is, the higher the resistance, and so the current in the wire is lower. This is because in a longer piece of wire there are more particles. It is harder to pass current through many particles than it is just a few.
- Diameter – As diameter increases, current increases. To explain this I will use the model of people going through a door. If the door is small, it will take people a long time to get through it. If the doorway is large, it will take the same amount of people a much shorter time to get through. This is the same as electrons moving through a wire.
- Temperature – When temperature is high, resistance is high. This means current is low. This is because when the wire heats up, the particles start to vibrate quicker. The vibrating particles restrict the flow of electrons, reducing the current.
- Voltage – Ohms Law states that when voltage increases, current will increase proportionally if the temperature is constant. This is because voltage is the push of electrons through a circuit. If the electrons have a bigger push, it is easier for them to travel through the circuit. This is why current increases.
- Resistance – Wires with a higher resistance will have a lower current flowing through them. This is because wires made of a resistant material restrict the electron flow through them. Wires with a low resistance are good at letting electrons flow through them.

Prediction –

I have chosen to investigate how length of wire effects current flowing through it. I have chosen this because it is easy to get a wide range of accurate results. Accurate results are achievable when varying the length because we can fix accurately all other factors. It is also practical to investigate length because it is available as a continuous variable, whereas area and resistivity are discrete variables.

I predict that the longer the length of wire, the higher the resistance and so the smaller the current in the wire. This is because a longer piece of wire has more particles, and so it is harder to pass current through many particles than just a few. This can be seen by looking on a small scale at the action of individual electrons (the flow of electrons is the flow of current). Electrons move in a metal to produce a current if there are two conditions;

1. There must be a potential (voltage) difference across the wire.

2. The electrons must be in the conduction band.

Electrons are given energy by the voltage provider (in our case a 2V power pack), which propels them into the conduction band. However, there are still small atoms in the way of the electron, and electrons don’t move from side to side to avoid obstacles. Every time an electron hits an obstacle it slows down and gives off some energy, thus the flow of current is reduced and the wire becomes slightly warmer.

The power pack must not be used for producing currents of more than 1A, and so our experiment will need to incorporate a variable resistor. This means that we can control the voltage across the wire and so get an equation for resistance R = V / I .

We can then get another equation for resistance from the “Salters Horners As Level Advanced Physics”, where resistance R = ρ l / A

So because;

Resistance= Voltage = Resistivity x length

current area

We can rearrange this formula to get;

Current = Voltage x area

Resistivity x Length

As we have known values for voltage, area, resistivity, and length, I can calculate predicted results, and draw a predicted graph.

For example at a length of 50 mm

Current = 0.2 x (9x10-8)

(110x10-8) x 0.05

Current = 0.33amps

I repeated this with every length of wire I plan to test, and have calculated the following predicted results.

Length of wire in mm | Predicted current in amps |

50 | 0.33 |

100 | 0.16 |

150 | 0.11 |

200 | 0.08 |

250 | 0.07 |

300 | 0.05 |

350 | 0.05 |

400 | 0.04 |

450 | 0.04 |

500 | 0.03 |

550 | 0.03 |

Diagram

Apparatus

- 1m nichrome wire, 26swg
- Power pack
- Variable resistor
- Voltmeter
- Ammeter
- 2 crocodile clips
- ruler
- 6 wires
- Micrometer Screw gauge

Middle

Safety

I will make the experiment safe by using a low voltage. I will turn off the experiment when changing the distance between the crocodile clips. I will not leave the experiment running for too long, as the wire will get hot and burn the table. I will keep the experiment away from water. I have used a variable resistor to ensure that the current does not exceed 1amp. This will prevent short circuits.

Fair Test and precision

I have kept the experiment fair I will control all factors, with the exception of length. I will keep the voltage in the current constant by adjusting the variable resistor. I will use the same piece of wire each time, this ensures that the type of wire, and diameter is the same. I will turn off the circuit between readings.

Conclusion

Anomalies occurred in my collected results. At a length of 100mm the current was higher than expected. This means that the resistance had decreased. The factor that changed this resistance was room temperature. The room must have been slightly colder when this reading was taken. This also occurred at a length of 500mm. At a length of 200mm, the current was lower than I expected. This means that resistance must have increased. Temperature increase is a factor that makes resistance increase. This result could be from the experiment being left running too long. The temperature of the wire would have increased, increasing resistance and reducing current.

My predicted results for current were all slightly lower than my collected results. This means that the resistance must have been lower than I calculated for my predicted results. The factor that effected resistance was room temperature. In my predicted results, the value for resisitivity of nichrome I used was for a room temperature of 20°c, whereas the room temperature when I carried out the experiment was about 18°c. At a lower temperature, the resisitivity of nichrome was lower. This would explain why my collected results all have a higher current than I expected.

If I were to extend the investigation into 'factors effecting current flowing through a wire' I would investigate another factor. Possibilities are diameter, temperature, voltage, and resistance.

Nicola Dearnley 10a1, 10fm

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

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