Light Bulb At Different Temperatures And Currents example essay topic

Physics Project The Planning Key V A Variable resistor Ammeter Light bulb Voltmeter I am carrying out an experiment to find the different resistances created by a light bulb at different temperatures and currents. Because of the nature of a light bulb, it glows white-hot when fully on, the resistance will change at different currents. When the current is low and the bulb is not very bright, it wont 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 temperature and 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. Variable Resistor Also called the Pedometer it acts in the same way as a normal resistor, to resist the current, but this one can have a variable resistance. To use the circuit, I will take readings from both the ammeter and the Voltmeter, when the variable resistor is in different positions.

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 30 results, hopefully all evenly spaced. The resistance is greater when the light bulb is hotter, because when any material is heated, the atoms making up that material vibrate over a larger distance more than they usually do. This vibration of atoms can get in the way of passing electrons and therefore results in fewer electrons getting through and a high resistance. Also, though the reason that the filament in the light bulb heats up and glows is because the electrons passing by at a normal speed will still knock into atoms.

Although it is not as frequent as at high temperatures, the electrons will cause the atom to vibrate. This is the action, which causes the heating of the filament. Above is a diagram of how electrons move around the material. This process wastes quite a lot of energy, because as the current increases, the resistance increases. This waste of energy can be greatly made up for by using super conductors, which are conductors that are super cooled. This would save energy but it then would not work for a light bulb, as the whole purpose of a light bulb is to create a resistance to make a light.

To measure the resistance for different power levels I will be using the Standard Test Circuit. This includes a voltmeter to measure the voltage around the bulb, an ammeter to measure the current, a variable resistor to make measurements of different currents, and the actual light bulb. 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 30 results, across different currents. This should let me do enough results to draw a firm conclusion, but will be within any time constraints. There is a basic, commonly used graph of an ideal lamp, showing the relationship of current and voltage.

The graph below is it. V This graph shows the ideal pattern of results for the experiment, but because we are working in a classroom environment, there are many factors such as minor room temperature fluctuations, contamination's 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 GCSEs Obtaining Evidence For this experiment I will be using a circuit called a Standard Test Circuit. It has a variable resistor, a light bulb, a voltmeter, an ammeter, and the power supply. A diagram of the circuit is below. This was OK until I started getting very low and I found I had to use 4 variable resistors, all on full power with only one cell to reach 0.02 A. Below is a table of results that I gained.

And also a graph of the results showing Current vs. Resistance and Current vs. Voltage. The Conclusion The results that I have obtained from the experiment are relatively near and therefore relatively true to the predicted graph line. This is surprising, as the conditions were not very controlled. Also there is a trend at the beginning of the graph. This is where the Voltage is not growing at a constant rate. After comparing my actual graph to my predicted graph, I have found that my actual graph does not have the same smooth curve that the predicted, example has.

This is once again because when taking the readings they are not perfectly taken. But also because to achieve a graph with a curve as smooth as that, not only do you need hundreds and hundreds of results, but you also it is impossible, because of any contamination may alter the results. Also in the graph at the beginning, it has a distinct sudden change. I think that this is because at this low power, the filament is not at a temperature much higher that the air temperature. At this temperature the example is truer, but then as the filament starts to heat up more and more, the difference in temperature from the air increases. This means that as the light bulb is given more power, the less it is heated more.

Also in theories, the heat is supposed to fluctuate at a constant current. This is because as the light bulb heats up, the resistance increases. This is because as the electrons flow through the wire, they hit into the protons of atoms and ricochet of them, slowing the electrons down and increasing the vibration of the protons. This then means that it is harder for the electrons to pass through the wire without hitting a proton, and hits them more times. This loops itself and increases the temperature and therefore the resistance. Then if the current is not change, it drops, due to the higher resistance.

This then decreases the current, decreasing the temperature, decreasing the resistance, and increasing the current again. Going on the results that I have obtained though, I would not say that the results are of a good enough standard to use as a firm conclusion. To extend the experiment even further I would increase the current to the maximum before it melts the filament. This would extend my result and graph to produce a more accurate curve. Also I could measure the current to 0.001 of an Amp.

This would also increase the accuracy but I would need to have more control over the environment. The Evaluation Overall my results have showed what I predicted, as the graph looks quite similar to the ideal one that I drew in my plan. To get a perfect result though, I would have to use more detailed and rigorous methods. One way may be to work out the resistance of the wire that I am using. The resistance of a material varies with temperature and the variation can be expressed by its temperature coefficient of a. If a material has a resistance R 0 at 00 C and its resistance increases R due to a temperature rise then a for the material is defined by the equation A = This can be rearranged to R = R 0 (1+ a) Using the temperature coefficient equation it is possible to find out the resistance from a given temperature reading, but I cant for this project because it is necessary to know what the resistance is at 00 C. This needs one of many measuring instruments such as digital thermometers and optical pyrometers.

I can use the thermometers to measure the physical temperature, but this would be quite hard, as I would not be able to measure it without touching the filament, which is in an airtight gas chamber. The optical pyrometer measures the temperature by the amount of light given off. This would be a lot easier.