Реферат: Physics Project Plan Essay Research Paper Physics

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.

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