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The aim of this experiment is to determine how resistance changes as the length of the wire increases.

Extracts from this document...

Introduction

T.Durden 11W

GCSE SCIENCE INVESTIGATION - PHYSICS: WIRE RESISTANCE

Aim:

The aim of this experiment is to determine how resistance changes as the length of the wire increases.

Planning:

Method:

A power pack, ammeter (in series), a meter rule (with nichrome wire running down the middle), a voltmeter (in parallel) and wires were taken. There were then connected up as shown above.

As seen above, there are two connectors on the meter rule. For ease, they are named clip A and clip B. Once the equipment has been set up, clip B is connected to one end of the meter rule (at 0cm). Then, for the experiment, clip A is moved at 10cm intervals away from clip B. For each interval, two readings (from the ammeter and voltmeter) are recorded, up until 100cm has been recorded. A diagram of the apparatus can be seen in fig 1.1. The wire that has been used is nichrome wire as it does not get very hot when there is high resistance in the wire. The heat caused by high resistance is due to unfixed electrons colliding with positive ions within the wire. These collisions cause the positive ions to vibrate more which in turn causes more collisions, which caused a higher internal energy of the wire, resulting in heat.

Theory:

Inside the wire there are electrons and positive ions. These positive ions are laid out in a lattice formation and can vibrate but not move out of the lattice grid. Some of the electrons are fixed and some are unfixed, which means that when a current passes through the wire, these unfixed (or free) electrons collide with the positive ions. This is what causes resistance. When current is applied across a piece of shorter wire, fewer collisions take place between the electrons and positive ions within the material. If the length of the wire is doubled, there is double the amount of positive ions in the wire, which means there is a higher resistance because there is a higher amount of collisions.

Therefore, the length of the wire is directly proportional to the resistance and because as the length of the wire doubles, the resistance doubles, the following predictive graph can be seen on fig 1.2. And so, based on this, I can predict that the length of the wire is directly proportional to the resistance and therefore as the length doubles the resistance will double accordingly.

The quantities that I intend to keep constant is the power supply (2 volts), see preliminary, and I will vary the length of the wire from a minimum of 10cm to a maximum of 100cm, again, see preliminary.

I intend however to change the length of the wire, of which will be tested at each length at different voltages.

The equipment that will be used is exceptionally accurate (to within 1/100th of an amp/volt) and this is therefore adequate for our needs. The formula which I will be using is as follows:

Resistance (R) = Voltage (V) / Current (I)

The number of measurements I intend to take is 1 reading starting at 10cm and at 10cm intervals to 100cm and one repeat for each reading.

Preliminary:

A preliminary experiment was carried out for a number of reasons based upon the validity and accuracy of the experiment. One cause of concern was to make sure that the resistance of the wire would not increase on a given voltage, so this was tested using a higher voltage, which then could determine at which point the wire became too hot, resulting in the range of voltages that could be used in this experiment. The circuit diagram for the preliminary experiment is shown in fig 1.3.

For the preliminary, to start with, the lengths taken were from 20cm-100cm at 20cm intervals. This gave a standard set of results that had equal intervals. The wire was then tested at 1v, 2v, 3v, 4v, and 5v, based upon the findings from the voltage heat test, which showed that above 8v the wire began to increase in heat and resistance. Another problem that was found was that because the wire had been stored in a coil, the wire when placed on the metre rule kept bending, and therefore for that reason, sellotape was used to fix the wire in position.

It took roughly 20 minutes to complete the preliminary experiment, and therefore when the main experiment was carried out, it was possible to do the experiment twice, thus enabling better accuracy with the results (using mean averages).

Preliminary Results:

Results for 1v:

 Length (cm) V (V) I (A) R (Ohms) 20 0.07 0.05 1.400 40 0.08 0.04 2.000 60 0.09 0.03 3.000 80 0.10 0.02 5.000 100 0.10 0.02 5.000

Results for 2v:

 Length (cm) V (V) I (A) R (Ohms) 20 0.70 0.53 1.321 40 0.77 0.32 2.406 60 0.80 0.24 3.333 80 0.82 0.20 4.100 100 0.84 0.17 4.941

Results for 3v:

 Length (cm) V (V) I (A) R (Ohms) 20 1.45 1.36 1.066 40 1.59 0.78 2.038 60 1.65 0.55 3.000 80 1.70 0.41 4.146 100 1.72 0.35 4.914

Results for 4v:

 Length (cm) V (V) I (A) R (Ohms) 20 2.26 2.12 1.066 40 2.48 1.23 2.016 60 2.56 0.88 2.909 80 2.62 0.68 3.835 100 2.65 0.55 4.818

Results for 5v:

 Length (cm) V (V) I (A) R (Ohms) 20 2.98 2.91 1.024 40 3.23 1.66 1.946 60 3.36 1.17 2.872 80 3.46 0.90 3.844 100 3.54 0.72 4.917

Middle

Obtaining Evidence:

Results for 3v:

 Length (cm) V (V) 1st V (V) 2nd V (V) Av. I (A) 1st I (A) 2nd I(A) Av. ResistanceR (Ohms) 10 1.36 1.38 1.37 1.67 1.71 1.69 0.811 20 1.42 1.49 1.46 1.30 1.32 1.31 1.385 30 1.52 1.54 1.53 1.03 0.97 1.00 1.577 40 1.58 1.59 1.59 0.76 0.81 0.78 2.038 50 1.61 1.62 1.62 0.64 0.67 0.66 2.456 60 1.65 1.63 1.64 0.52 0.59 0.55 2.982 70 1.67 1.65 1.66 0.46 0.45 0.46 3.609 80 1.70 1.71 1.71 0.39 0.42 0.41 4.171 90 1.71 1.72 1.72 0.36 0.37 0.37 4.649 100 1.72 1.74 1.73 0.34 0.36 0.35 4.943

Results for 4v:

 Length (cm) V (V) 1st V (V) 2nd V (V) Av. I (A) 1st I (A) 2nd I(A) Av. ResistanceR (Ohms) 10 2.11 2.13 2.12 2.61 2.65 2.63 0.806 20 2.24 2.25 2.25 2.11 2.13 2.12 1.061 30 2.35 2.37 2.36 1.69 1.64 1.67 1.413 40 2.50 2.48 2.49 1.21 1.20 1.21 2.058 50 2.53 2.53 2.53 1.04 1.06 1.05 2.410 60 2.56 2.57 2.57 0.90 0.87 0.89 2.888 70 2.59 2.61 2.60 0.79 0.81 0.80 3.250 80 2.63 2.65 2.64 0.70 0.66 0.68 3.882 90 2.64 2.65 2.65 0.60 0.62 0.61 4.344 100 2.65 2.66 2.66 0.54 0.55 0.55 4.836

Results for 5v:

 Length (cm) V (V) 1st

Conclusion

I found the procedure of the experiment was, although successful, appeared to have many factors which could be improved. One of these was the fact the storage conditions of the wire had led to it being difficult to lay it flat, and therefore sellotape had to be applied. Sellotape, being an insulator does not allow the jockey to pass over it, unless being removed. So a new type of fixate should be used to hold the nichrome wire in position.

If this experiment was to be repeated, or if one was trying to provide additional relevant evidence, it would be an interesting idea to investigate the resistance changes based upon a material with a different conductive value. E.g. the prospect of using different electrical conductors to see which produce the most resistance. This would be interesting to investigate and would produce a whole new set of data.

Physics - Science Investigation

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