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# Investigating how the length of a wire affects resistance.

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Introduction

DamiG®                                                               2003

Investigating how the length of a wire affects resistance

Theory:

What is resistance? Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and therefore move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat.

Aim:

In this investigation I am going to experiment to find out how the length of a wire affects its resistance.

Prediction:

I predict that the longer the piece of wire, the greater the resistance will be. This is due to the idea of the free moving electrons being resisted by the atoms in the wire. In a longer piece of wire, there would be more atoms for the electrons to collide with and so the resistance would be greater. The relationship between the wire length and the resistance should be directly proportional.

Middle

Experiment Results:

Experiment A

 Length(cm) Voltage(Volts) Current(Amps) Resistance(Ohms) 5cm 1.50V 1.95A 0.77Ω 10cm 2.00V 1.30A 1.54Ω 15cm 2.00V 1.00A 2.00Ω 20cm 2.10V 0.80A 2.63Ω 25cm 2.20V 0.65A 3.38Ω 30cm 2.30V 0.55A 4.18Ω

Experiment B

 Length(cm) Voltage(Volts) Current(Amps) Resistance(Ohms) 5cm 1.60V 2.00A 0.80Ω 10cm 1.90V 1.40A 1.36Ω 15cm 2.00V 1.00A 2.00Ω 20cm 2.10V 0.85A 2.47Ω 25cm 2.20V 0.70A 3.14Ω 30cm 2.30V 0.60A 3.83Ω

Experiment C

 Length(cm) Voltage(Volts) Current

Conclusion

Other factors that change resistance

One factor that changes resistance is density. It has a large affect on the amount of resistance. The resistance depends upon the amount of denseness e.g. a large surface area has less resistance because a small area has tightly packed atoms which in turn rebound many of these electrons. Temperature has an affect on the experiment as well because the voltage has control over the temperature. The more the temperature increases the more the particles vibrate leading to a reduction in output voltage although not by a huge amount; this does have an affect.

And finally, the type of wire will depend on it’s resistance for example a nickel chrome wire’s resistance may be totally different to that of a constantan wire which I used.

Evaluation:

I don't think I could improve the experiment because it worked very well and got me some accurate results. I also found the experiment quite easy to set up as well. A further experiment I could do would be to see how the diameter of a wire affects the resistance. This would be very relevant because it is similar to the experiment I have done. However, I already know that other factors to affect the resistance are density and thickness because a thinner wire’s atoms are more tightly packed than those of a thicker wire.

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