p5 investigation cwk- resistance of a lightbulb

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                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. I will then use the voltage and current to work out the resistance using the formula R = V / I.

I had set up this investigation to see whether the voltage flowing through a light bulb affected the resistance. I conducted the investigation by setting up a simple circuit, which is illustrated by the circuit diagram below.


Equipment -

  • Filament Light Bulb - To test the resistance of a filament light bulb
  • Connectors - To connect the circuit together
  • Power Supply - To power the circuit so the resistance can be calculated
  • Rheostat - A variable resistor so the voltage can be altered accurately (I had chose to use this because I could alter the voltage flowing through the current accurately)
  • Digital Ammeter - So the current flowing through the circuit can be measured (I had chosen a Digital Ammeter because it measures the current to greater accuracy)
  • Digital Voltmeter - So the voltage flowing through the circuit can be measured (I had chosen a Digital Voltmeter because it measures the current to greater accuracy)

Method -

  1. Collect and arrange equipment
  2. Connect Power Supply and add wires from the DC current.
  3. Connect a digital ammeter, moving the dial to DCA 10A, and a rheostat to each end of the wire.
  4. Add connectors to the end of the digital ammeter and the rheostat.
  5. Connect each end of the wires to a light bulb fixed into a holder.
  6. Use the rheostat to control the voltage, moving the dial to DCV 20V and take reading of the voltage flowing across the light bulb and the current flowing through the circuit.

I had conducted a simple experiment by connecting a power supply, an ammeter and a bulb with a voltmeter connected in parallel. I turned on the power supply and started to adjust the voltage, by moving the bar of the rheostat - which shows me whether the voltage affected the current. The table below shows the results that I have collected.

Preliminary Table of Results -

From these results I can see that once I had increased the voltage, the current also increased which meant that there was a rise in resistance. From looking at the results I can see that some results are inaccurate, are outliers, which shows that it was not measured correctly. Also there is not an equal rise between voltages as we can see high jumps between the voltages. I believe this is because I was concentrating in the equal jumps on the rheostat. In my Final Plan I decide to concentrate on the equal jumps in voltage as this will help me gain accurate results.

Final Plan -

While completing my Final Investigation I had decided to concentrate on the equal jumps in voltage to see whether it affected the resistance of light bulbs. To have done investigation correctly, I started to move the dial so it was set to a particular voltage. Also I decided to use another smaller bulb with a decreased wattage to ensure that the conclusions that I had made are correct. For this experiment I completed the investigation with a 5W and 24W Filament Bulb, recording the voltage and current at particular intervals.

The changes that I have made from my preliminary plan to my final plan are stated below:

  • In my preliminary investigation I was concentrating on the equal jumps of the rheostat. This meant that the results that I have collected are not varied. In my final investigation I took measurements of the voltage at particular intervals which meant that I could get a variety of results.
  • Another change that I made was that I investigated a further type of light bulb. In my preliminary I only investigated a 24W light bulb. In my final I decided to also investigate into a 5W light bulb to see whether it made any difference to the resistance.

Final Table of Results -

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GRAPH FOR FINAL RESULTS ON VOLTAGE - 5W AND 24W FILAMENT BULBS


Conclusion for Final Plan -

Voltage -

From the analysis of both results I can see that once the voltage is increased the current increased alongside. From using the formula R = V / I, I can see that the resistance increased once I had increased the voltage. This shows that the voltage flowing through a light bulb affects the resistance. I believe this is because the filament of the 5W bulb is ...

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