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# To investigate how the resistance of a wire is affected by the length of the wire.

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Introduction

## Resistance of a Wire Coursework

Resistance of a Wire

To investigate how the resistance of a wire is affected by the length of the wire.

Theory:

What is resistance?

Electricity is conducted through an object that is a conductor, in this case a length of wire, by the means of free electrons. The number of free electrons is dependent on the material and more free electrons means a better conductor, i.e. it has less resistance.

### Ohm’s law-

Ohm's Law deals with the relationship between voltage and current in an ideal conductor. This relationship states that:

The potential difference (voltage) across an ideal conductor is proportional to the current through it.

The constant of proportionality is called the "resistance", R.

Ohm's Law is given by:

V = I R

Where V is the potential difference between two points, which include a resistance R. It is the current flowing through the resistance. For biological work, it is often preferable to use the conductance, g = 1/R; in this form Ohm's Law is:

I = g V

Material that obeys Ohm's Law is called an ohmic conductor or a linear conductor because the potential difference across it varies linearly with the current.

Ohm's Law can be used to solve simple circuits.

Middle

5.6

0.1

At 6 Volts:

 Length of wire (CM) Voltage (V) Current (A) Resistance (Ω) 100 2.5 4.7 0.5 90 2.3 4.8 0.5 80 2.2 4.9 0.4 70 2.0 5.0 0.4 60 1.9 5.1 0.4 50 1.7 5.3 0.3 40 1.4 5.5 0.3 30 1.3 5.6 0.2 20 The wire just Melted ------------------------- 10 The wire just Melted -------------------------

From these results I have decided that I am best to use 4 volts in the actual experiment, as it provided results from 10cm up to 100cm and the higher voltage provided no additional ease of measurements. I have also decided from these results not to use Brass wire, because this is what I have used for these preliminary experiments and as you can see it produces a set of not very good results, and because of this I will not use Brass wire for my actual experiment. However the results that I have got are good enough for preliminary results, meaning that the results show that my design for the experiment works, it is also beginning to show that my hypothesis is right.

As I mentioned in the method I need to allow the wire to cool down between the experiment s simply because the temperature will affect the resistance, and so by allowing the wire to cool before continuing with the experiment I can quite safely assume that the experiment will be a fair one.

Safety:

As I have seen in my preliminary experiments, that a short length of wire can result in over heating of the wire and it quite simply melting. I have decided to use a low voltage of 4 volts so that in the actual experiment I would avoid problems with overheating of the wire. I have also decided not to do any lengths lower than that of 10cm, which will also help to stop the problem of overheating.

Results:

Wire 1- Nichrome 0.45mm in diameter.

 Length of Wire (CM) Voltage (V) Current (A) Resistance (Ω) 10 2.0 2.7 0.7 20 2.3 1.7 1.4 30 2.5 1.2 2.0 40 2.5 0.95 2.6 50 2.6 0.78 3.3 60 2.7 0.64 4.2 70 2.7 0.57 4.7 80 2.8 0.5 5.6 90 2.8 0.45 6.2 100 2.8 0.4 7.0

Conclusion

• The length needed for that result was not measured accurately, if it were too long it would have caused a higher resistance and if it were too short it would have caused a lower resistance. If I were to redo this experiment I would measure the Created by userwire more accurately by ensuring that the wire was pulled tight against the ruler.
• Or for that particular result one of the connections was loose (or just plain faulty) which could have caused extra resistance meaning that the result was higher than it should have been. I could stop this by simply connecting the connections in place when the wire is not in place before each experiment, and measuring the resistance then, and if it is higher than the connections should be either cleaned or replaced.
• Although it is far fetched it could be that the PSU (power supply unit) is supplying a slightly incorrect voltage to the circuit. This is very unlikely but it would be an issue if we were using batteries to power the circuit.
• Also as I have mentioned before if the lengths of wires have not had chance to cool then that will also be affecting the resistance, so I could prevent this from affecting it by allowing the wire to cool for a certain period of time before the next experiment.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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