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# Experiment to investigate the resistance of a wire.

Extracts from this document...

Introduction

GCSE Physics

## Introduction and planning:

Electrons move through when a p.d. is applied. The opposition of a conductor to current is called its resistance. Resistance is measured in ohms (Ω). Flow of electrons is called current. Voltage is the force, which pushes the current round the circuit and the resistance opposes it. This means that there is a relation between these three.

Current decreases when resistance increases. This is Ohm’s law.

V=IR

Therefore

R=V/I

A resister has the resistance of one ohm if a voltage of one volt is requires to push the current of one amp through it. If the electrons travelling along the wire collide with the atoms of the wire, resistance occurs. Since flow of electrons slows down because of these collisions therefore resistance increases and current decreases.

According to these rules, there are few factors, which can affect the resistance.

Length of the wire (L):

If the length (L) of a wire increases, its resistance will increase. The reason is that electrons have to travel longer, so there will be more collisions. If the length of a wire doubles, the resistance will be double.

Hence resistance is directly proportional to the length.

R∝L

Cross sectional area of the wire (A).

The resistance decreases with width (of wire). The reason is that electrons have more space, so there will be fewer collisions causing less resistance. If the cross-section area of a wire doubles, the resistance will be half.

Middle

0.6

20

0.50

0.39

1.3

30

0.53

0.29

1.8

40

0.55

0.24

2.3

50

0.58

0.19

3.1

Main experiment.

Apparatus.

1. Battery; (4volts)

2. Voltmeter; to measure voltage

3. Ammeter; to measure current

4. Crocodile clamp; to connect the wire (28SWG CONSTANTAN) to the circuit

5. Five connecting wires;

6. Variable Resistor (Rheostat);

7. Tapping key.

8. Metre ruler.

Safety.

I need to consider safety whilst carrying out the experiment. I will be careful when handling live wires. After taking one readingI will switch off the battery. Then I will measure the length of the wire for next reading.

Variable factor.

The only variable is the length of the wire.

Constant factors.

For every reading these will stay constant.

Wire (28SWG CONSTANTAN);

Temperature of the wire (room temperature);

Voltages (4volts);

Diameter of the wire (0.3759mm).

Circuit diagram.

Battery (4volts)

Rheostat

Mere rule and wire

Tapping key
Ammeter     Crocodile clamp      Voltmeter

I have decided to start from 20cm because at 10cm resistance was very low. I will increase them by 20cm to get high readings because with high readings I can plot graph easily.

It is always good to repeat the experiment. I decided to get two readings for every different length using Rheostat. Then I will get the average. The readings I am going to use are 20cm, 40cm, 60cm, 80cm, and 100cm. I have chosen these readings as I can measure them easily by meter ruler. Since the Ammeter I used is 0  5 scale, therefore I will divide the readings by 10 to bring it down to 0 1 scale.

## Method.

1. I drew results table.

2. I set the circuit as I shown in the diagram.

3.

Conclusion

I did not get any anomalous result. Three points are not fitting the line but they are extremely close to the line showing that there must have been a very slight error in my experiment. In my thinking the reason for this is that it was very hard to stretch out the wire and consequently, measure it accurately.

To improve my results,

1.I would do more preliminary work to make my method more accurate and that I was more familiar with doing the experiment.

2.I think it would be a good idea to repeat the experiment more than two times. It will improve average results.

3.I think it would be better to work with another person so one person will put devices together while other will check (and write) the readings.

4. Iwould use pointers instead of crocodile clamp because the tips have a smaller area and would give more accurate measurement of the wire.

5. I would use a digital Voltmeter to get more accurate readings.

6. I would control the room temperature as I just assumed 20°C in this experiment.

Additional work could be carried out to repeat the experiment using a wider range of lengths. The investigation could also be extended to investigate other factors, such as different widths of the same wire and different types of wires.

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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