Physics Project Plan Essay, Research Paper
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 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 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 Pecometer 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 higher 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 GCSE?s 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. V (volts) I (amps) R (ohms) V (volts) I (amps) R (ohms) 0.03 0.02 1.5 1.23 0.16 7.69 0.04 0.03 1.33 1.38 0.17 8.12 0.06 0.04 1.5 1.63 0.18 9.06 0.07 0.05 1.4 1.87 0.19 9.84 0.09 0.06 1.5 2.01 0.20 10.05 0.10 0.07 1.43 2.2 0.21 10.48 0.15 0.08 1.86 2.37 0.22 10.77 0.23 0.09 2.56 2.6 0.23 11.30 0.37 0.10 3.7 2.86 0.24 11.92 0.52 0.11 4.73 3.1 0.25 12.4 0.71 0.12 5.92 3.37 0.26 12.96 0.82 0.13 6.31 3.58 0.27 13.26 1.03 0.14 7.36 3.82 0.28 13.64 1.15 0.15 7.67 4.24 0.29 14.62 4.44 0.30 14.8 ???????? Using
this test circuit, I worked by finding out the voltage for every 0.01 Amps.
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 0.02A. 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 ConclusionThe 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 R0 at 00C and
its resistance increases δR due to a temperature rise δθ then a for the material is defined by the
equation A =? ___?? ___ ? This can be rearranged to Rθ = R0
(1+ aθ) 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 00C.
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.