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# This experiment will show, by using the volts and current to calculate in an equation, how the length of a piece of wire will affect its resistance. The varying length of the wire should back up my scientific ideas.

Extracts from this document...

Introduction

### AMALIE SILVANI - JONESPhysics coursework

##### AN INVESTIGATION INTO HOW THE LENGTH OF A WIRE EFFECTS ITS RESISTENCE

Planning

INTRODUCTION

This experiment will show, by using the volts and current to calculate in an equation, how the length of a piece of wire will affect its resistance. The varying length of the wire should back up my scientific ideas.

Equipment I am using

• A Voltmetre
• An ammeter
• A ruler
• Wire cutters
• tape
• A power pack
• 5 pieces of wire
• 2 crocodile clips
• 1 piece of chosen wire to vary in length

SCIENTIFIC IDEAS

Resistance is caused by electrons colliding with the atoms that metals are closely packed with; this collision slows down the electrons flow. This therefore reduces the current flowing through a circuit. The intensity of the resistance is measured in Ohms (named after its creator George Ohm)

George created a law called “Ohms law”- which states that the current flowing through a metal wire is proportional to the potential difference across it (if the temperature stays the same).

Factors that affect resistance in a wire are:

• As the temperature increases, the resistance increases.
• As the length of the wire increases, the resistance increases.
• As the thickness of the wire increases, the resistance decreases.

The length of a wire also plays a great part in the resistance of the wire.

Middle

I will be using the constantan at a thickness of 28swag throughout the experiment. I found that when I used constantan at 32swag, it burned a lot easier then the constantan at 28swag.

I will be testing the wire at five different lengths- 10cm, 20cm, 30cm, 40cm, and 50cm. I found that this will give me a good, wide spread of results, and give me a clear idea of the pattern.

PREDICTION

I predict that as the length of the wire increases, the resistance will increase. I predict that the voltage readings on the voltmeter will increase as the length of wire increases, and the current reading on the ammeter will decrease. I predict this because as the length increases so will the resistance, therefore the voltage will increase and the current will decrease because it will become increasingly harder for the electrons to flow through the lengthening wire.

FAIR TEST

To ensure a fair test, the experiment will need to be repeated 3 times for each length. If any obvious anomalous results occur during the experiment, I will repeat the experiment until the results are reliable. The following experimental conditions need to be kept constant:-

• The wire will need to be kept at the same temperature throughout the experiment; this can be achieved by not passing too much current through the wire (keeping the time that the power pack is switched on to an absolute minimum) and waiting in between taking the results for the wire to cool down.
• Also as this experiment will be carried out in air the room temperature should remain constant.
• The voltage also needs to be kept constant. I have chosen to use a voltage of 3v on the power pack– after looking at the results of my preliminary experiment (the current is not too high and not to low).
• The voltage through the circuit will be measured using a voltmeter placed in parallel in the circuit and the current will be measured using an ammeter, placed in series in the circuit- so that I can work out the resistance.
• To make sure the cross sectional area (thickness) of the wire remains constant, the same piece of wire – with the same amount of swag - will be used throughout the experiment.
• Ensure the wire remains straight, (but not under tension), so that accurate readings can be taken. I will do this by cello taping it to a 50cm ruler.

To insure that the temperature of the wire doesn’t effect the results as the wire gets hotter due to high currents, I will make sure that the power pack is only switched on for a matter of seconds, and after every recording Is taken I will wait for the wire to cool down (with the power switched off) for approximately 1minute to ensure that the wire is back to its original temperature for a fair test of the next reading.

SAFETY

• The Voltage input from the power pack will remain at 3volts throughout the experiment and will not be altered with – therefore avoiding the cause of unnecessary wire burning and skin damage.
• I will not overload the ammeter and voltmeters with current, as this will blow their fuses and they will cease to function.
• I won’t short-circuit any of the components, or power source.
• I will act responsibly at all times in the Laboratory with regard to personal safety and the safety of others.

Conclusion

There are problems of measuring the actual length as crocodile clips were used. Each crocodile clip is about 5mm broad and has jaws with two sides, which clip on to the wire. It is assumed that the side of the jaw, which was placed at the actual distance that the recording was made, was in fact making the actual electrical contact. However there was no way of determining this at the time of each test. A more accurate result would have beeN possible if a plate had been bolted to the wire at zero and a clamp with a single jaw had been slid along the wire at each measurement. This may have been one of the reasons that the readings taken varied slightly and may be the reason for the inaccurate result obtained at 1050mm.  The actual length measurement could also have been improved if a veneer scale had been used rather a direct visual reading

When looking at Graph B, (as all of the points lie extremely closely to the straight line), I conclude that the experiment produced very accurate results, even though the apparatus used had its limitations of accuracy.

AMALIE SILVANI - JONES

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