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# p5 investigation cwk- resistance of a lightbulb

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Introduction

GCSE Science

Investigating the Factors that Affect the Resistance of Light Bulbs

In this investigation I will be investigating the factors that affect the resistance of light bulbs. I will be conducting a variety of experiments to investigate this by using a range of equipment. From my results I will explain and come to a conclusion in outlining what factors affect the resistance of light bulbs.

Resistance is the opposition that is created to the flow of electric current. The standard unit of measurement is Ohms (Ω). The resistance of a component is calculated by dividing the Voltage (V), which is measured in volts by the Current (I) which is measured in amperes. The formula beside illustrates how the resistance can be calculated. From looking at the factors that affect the resistance of light bulbs I can see that there are five factors that affect the resistance. These factors are:

• The Voltage Across the Circuit
• The Type of Wire
• The Length of the Wire
• The Area of the Wire
• The Temperature of the Wire

Preliminary Plan -

Before conducting the experiment I had conducted a preliminary experiment. The preliminary investigation helped me analyse whether my method that I was using was suitable and indicated to me any changes that I might have to make while conducting my final results.

To complete the investigation I will need an independent and dependant variable. The independent variable is the variable I will be changing throughout the investigation, which will help me, investigate the what factors affect the resistance of light bulbs. As my independent variable I have chosen the voltage flowing through the circuit. I will also need a dependant variable, which is the variable I will be measuring. I have chosen the current flowing through the circuit as my dependant variable.

Middle

Secondly I have also decided to investigate how the type of filament wire affects the resistance of light bulbs. I have decided to use different types of wire, while controlling the length and voltage. The different types of wire that I will be using are constantan, manganin and nichrome. By using different types of wire present in light bulb filaments I can see how difference in material of filaments affects the resistance of light bulbs. During the experiment I had to keep some factors in control. The factors that I will control are the thickness and length of the wire, keeping the wire at 0.6m length and at 24SWG.

Additionally I have decided that I will be investigating how the difference in cross sectional area of filaments affects the resistance of light bulbs. To complete this investigation I will be using different thicknesses of constantan. I have chosen to use constantan because it is the most common material used as filaments in light bulbs. During the investigation I will be keeping the length of wire – 0.2m and the material of the wire the same - constantan. This will help me conduct a fair experiment allowing me to come to an accurate conclusion.

Finally I have decided to investigate how the temperature of the light bulb affects the resistance. I have placed the filament submerged under water so all the heat energy will be absorbed - keeping the filament at a constant temperature. I have used a 24W bulb and have measured the voltage and current at different stages.

Equipment List -

• Filament Light Bulb - To test the resistance of the light bulb
• Connectors - To connect the circuit together
• Crocodile Clips - To connect the different types of wires to the circuit.
• Power Supply - To power the circuit so the resistance can be calculated
• Rheostat - A variable resistor so the voltage can be altered
• Digital Ammeter - So the current flowing through the circuit can be measured
• Digital Voltmeter - So the voltage flowing through the circuit can be measured
• Constantan, Manganin and Nichrome Wire - So I can investigate how different material filaments affect the resistance of light bulbs
• Beaker and Water - So the temperature can be measured as the filament is submerged under water
• Ruler - To measure the amounts of wire
• Wire Cutters - To cut the different length wires
• Micrometer - So the width of the wire can be measured.

Conclusion

During my investigation I believe that the results collected are accurate as all my results collate to fit with a general trend. There are two sets of anomalous results, one for my preliminary results and the other for my results on how temperature affects resistance. Once I had experienced the outliers with the preliminary results I had made all necessary changes which guaranteed that there were no more outliers in my further experiments. Additionally I had faced a few problems with the temperature. I had got many outlier results which I believe was because the water did not absorb the heat energy effectively. Once the water had been heated, the heat energy stayed with the filament, causing the resistivity to rise, meaning that my results were inaccurate. To ensure that I would not have any outliers I would repeat the experiment and also keep the temperature constant by the use of different substances.

To evaluate my results I have also used mathematical formulas such as gradient calculations and the resistivity formula. The mathematical data, alongside my results help me prove that the data I have collected is reliable which ensures that the conclusions I have made are correct. Also from the analysis of the graphs with range bars I can see that they are relatively low. For my results on length, the highest range is 0.11 and it is the same for area. This suggests that the results I have corrected are relatively accurate and precise.

All the factors above show that I have collected reliable and accurate data, which I have used to make valid conclusions. The main improvement that I would make would be that if more time was given, I would repeat the experiment to make secure conclusions. Overall I believe that I have completed the investigation to a high standard and have collected enough reliable data to come to accurate and precise conclusions.

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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