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# Factors that affect the resistance of a wire

Extracts from this document...

Introduction

## Introduction

We are investigating the factors that affect the resistance of a wire. The following factors affect the resistance of a wire.

• Thickness of the wire
• Type of metal of wire
• Temperature of wire
• Length of wire
• Area of the wire
• The thickness of a wire effects it because of the amount of space the electrons have for movement for example If there was a thin wire and a thick wire then the thin wire would have the most resistance because there is less space for the electrons to move through the wire.
• The type of metal affects the resistance because each type of metal has a different arrangement of electrons, and each has different numbers of electrons in its valence shell. There are positive ion cores which the electrons have to avoid, or get round, as they travel through the wire. The type of metal will affect how large and how close to each other these cores are. This will affect how easy it is for the electrons to get through, and therefore affect the resistance.
• When we increase the temperature of a material the positive ion cores begin to vibrate more vigorously. This also makes it harder for the electrons to pass by, increasing the resistance. So resistance increases with temperature. The wire that we are using (constantan) is an alloy it shows very small changes of resistance with temperature. (Researched in Physics for today). However according to Ohms law the resistance of a metal is the same whatever current is flowing – provided the temperature doesn’t change, so temperature change must be considered.
• The length affects the resistance of a wire, because the electric current has further to travel along the electrons
• Ohms law states that if the cross section of the wire is uniform then the resistance is proportional to the length and inversely proportional to the area of the cross section

Middle

In general increase of temperature increases the resistance of metals, but decreases the resistance of non- metals. The wire that we are using constantan is an alloy, and it shows very small changes of resistance with temperature. (I researched this Physics for today)

Length of wire (cm)                  Current (A)             Voltage (V)          Average Resistance(V / I)

20.0                                       0.55                         1.20                                    3

30.0                                       0.31                         2                                         6.5

40.0                                       0.25                        2.4                                       9.6

50.0                                       0.16                        2.4                                       15

I decided that I would start my length of wire at 50cm, I decided to do this because I want to have six sets of results and I want them across a good range so I decided at this.

## Results of prelim

Fair Test.

• I will repeat each length of wire three times to gain an average
• I will keep the number of batteries the same (2)
• I need to make sure that there are no kinks in the wire otherwise it will be an unfair experiment. I could also measure at different points along the wire.

## Safety

• Be careful of the wire, as it will get hot as the electrons start to move faster.
• A heatproof mat must be placed under the wire.

## Plan

1. Collect apparatus (as shown in list of equipment)

Conclusion

We didn’t have a temperature control, to improve this we could put the wire in something that has a constant temperature for example water, this would have made sure that the temperature would not increase and affect out results, and make them unfair.

We did get an anolymous result for 70cm; the reason for this was because the current was lower for 70cm than 60cm. For further research I could repeat the experiment for the length of 70cm, to see if the result fitted in with my line of best fit as the length could have been slightly different, or perhaps I read the voltmeter or Ammeter wrong. However I researched someone else’s result was the resistance of 70cm. This fitted in with my line of best fit, as shown in my graph (see purple cross).

We could look at other factors that affect the resistance for example, we could look at how the thickness of a wire affects the resistance of a wire. The formula for my prediction graph was   y = 0.4 x ,my formula for my graph was  y = 0.11 + 2.4. This is quite a difference the reason for this is because in my preliminary I started my length at 20cm where in my plan I started my length of wire at 50cm.

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