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# What factors affect the resistance of a wire?

Extracts from this document...

Introduction

Amie Mustill

What factors affect the resistance of a wire?

Although the current and the potential difference (voltage) measure different things, they are related to one another. If a battery is connected to a length of wire, it is possible to measure the current through the wire using 1, 2, 3 or 4 cells. By doing this, it is possible to find a simple relationship between the potential difference across the ends of a wire and the current through it. This being that doubling the potential difference doubles the current. Repeating the investigation for other types of wires provides results displaying a similar relationship between potential difference and current. Voltage current graphs are always straight lines through the origin, although the slopes are different. In 1826 a German physicist called Georg Ohm first discovered this relationship between potential difference and current. Ohm’s law states that:

“Provided the temperature and other physical factors remain constant the current

through a wire is proportional to the potential difference across its ends.”

If the potential difference across the ends of a wire is divided by the current through it, we get a constant figure for a given piece of wire. This figure is the resistance of the wire and represents the wires opposition to current. Ohm’s law can

Middle

• 1 piece of constantan wire of length 110cm
• 2 crocodile clips
• A power pack (plugged into a power supply)
• Digital voltmeter
• Digital ammeter
• Metre rule

## Method

Before I begin the experiment I will set up the required equipment as displayed in the diagram above. Once all of the equipment is in place I will begin by placing the crocodile clips (attached to the leads) 10cm apart (measure using the metre rule) along the 0.3mm diameter piece of constantan wire. I will then turn on both the digital ammeter and digital voltmeter, before switching on the power supply, followed by the power pack, which should be set at 3 volts. I will then record the readings that both the voltmeter and the ammeter display before switching off the power pack. Having recorded measurements for the voltage and the current I am then able to use the formula R= V/I

(R= resistance (ohms), V= Voltage (volts), I= Current (amps)) to work out the resistance across the wire. Once the readings have been recorded and the resistance calculated, I will repeat the procedure twice (total of three). I will then carry out the same procedure when the crocodile clips are 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm and 100cm apart. Once all ten measurements have been completed, I will repeat the experiment a further two times (total of three) using two different piece of 0.

Conclusion

The results that I obtained whilst finding out what affects the resistance of a wire were both accurate and fair and corresponded to the secondary evidence that I had found. I came across irregular results whilst carrying out preliminary experiments. These anomalies were due to the high resistance, which increases the temperature of the wire and affects the resistance. However, this allowed me to decrease the resistance for my final experiment and as a result I did not come across any anomalies and in many cases I recorded the same resistance for a length of wire more than once. Therefore, I feel that the results that I have collected are sufficient and support my conclusion.

The experiment that I performed was very suitable and it produced accurate results, but if I were to perform it again, I would improve it by:

• Finding a better method of measuring the distance between the two crocodile clips because I do not feel that using a meter rule was accurate enough
• Testing a wider range of measurements
• Use the actual lengths of wire rather than measuring the distance between two crocodile clips

There are many other experiments that I could perform in order to find out what affects the resistance of a wire, such as:

• The diameter of the wire
• The type of wire
• The temperature of the wire
• The voltage
• Test a wider variety of measurements

Bibliography

BookAuthor

Advanced Chemistry for you                                Lawrie Ryan

AS Chemistry                                                Andrew Hunt

AS Chemistry                                                Rob Ritchie

Chemistry in Context                                        Graham Hill And John Holman

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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