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To find out what happens in the filament of a bulb as we increase the voltage through the bulb.

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Introduction

Physics Investigation Aim: To find out what happens in the filament of a bulb as we increase the voltage through the bulb. I am carrying out an experiment to find the different resistances and currents created by a light bulb at different voltages. Because of the nature of a light bulb, it glows white-hot when fully on, the resistance will change at different voltages. When the voltage is low and the bulb is not very bright, it won't be as hot and therefore it will have less resistance. But when the current is high and the bulb is brighter, it will have a high resistance. I will be using the following circuit for the experiment: Definitions: Ammeter: This is a device that measures the current of electrons in Amps. It has to be placed in series on the circuit. Voltmeter: This is a device for measuring the potential difference of the electrons in the circuit. They are measured in Volts. It is placed in parallel. To use the circuit, I will take readings from both the ammeter and the Voltmeter. I will need to try and get results that are high and ones that are low, and try to have an even distance between each result. I will take down the readings from both the ammeter and the voltmeter. I should end up with 36 results, three results from twelve different voltage settings, hopefully all evenly spaced. ...read more.

Middle

* I will measure each voltage a total of three times. Then using the mean method of working out averages, I will work out an average, which will be used on my graph. This will ensure that any anomalous results won't totally destroy the experiment. If any result is blatantly wrong on my part, I will retake it to make it slightly more reliable. I will write down the results that I have retaken. * Because we are working in a classroom environment, there are many factors such as minor room temperature fluctuations, contaminations in the wiring materials, non-accurate measuring instruments and a non-accurate power supply. All the above factors could be improved upon to give more accurate and true results, but this would be quite unpractical on the level that we are doing the experiment for GCSE's For the experiment, the ideal amount of results is thousands, but because of the restraints of the accuracy in the classroom and the time period, I will be working with about 36 results, across different voltages. This should let me do enough results to draw a firm conclusion, but will be within any time constraints. The Results: Volts Amps A2 A3 Ave V/I=R 1 0.8 0.9 0.85 0.85 1.17 2 1 1 1 1 2 3 1.2 1.2 1.2 1.2 2.5 4 1.3 1.4 1.3 1.3 3.1 5 1.4 1.5 1.45 1.45 3.45 6 1.5 1.6 1.5 1.53 3.92 7 1.7 1.8 1.65 ...read more.

Conclusion

If I was going to create a really detailed graph and draw the most perfect upward curve ever, I would probably need to take down hundreds, maybe even thousands of results at least five times to get a very concrete conclusion, but this is quite unrealistic with the limited time and patience GCSE students have. Also, the school equipment is pretty poor standard compared to laboratory equipment, and it comparatively unreliable and inaccurate, and it could produce a glitch in my results. If I had more time, I could try the investigation with different equipment to what I had already used. This could prove that the equipment I used doesn't matter in the experiment, and it's the fact that how I carry it out which is crucial. To extend the project further, we could carry on the voltages to twenty, or twenty-five to see what happens to the results and graphs then. We even could carry the experiment on until the filament melts, and see how much voltage it can tolerate. Also, we could add a lamp or two into the circuit and see if this affects the resistance, voltages or the resistance in any way. Maybe instead of a variable power supply, replacing it with a couple of cells and also adding a variable resistor into the circuit. I would like to know if these affect the filament in anyway, and see if affects the resistance or current in anyway. It would be interesting to find out anyway. Kieran O'Connor 11BR ...read more.

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