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Physics GCSE |
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By Heresh Rezavandi
Introduction:
In this investigation I will be investigating which length of constantan wire of 12 different lengths ranging from 10 cm to 100 cm is the best heating element that outputs the most heat when they are individually resisting current.
Any length of constantan wire will resist current since constantan is an insulator. Because it is an insulator there is resistance, that is resisting current. This is due to the collisions between the electrons of the current and the atoms of the constantan wire. If there are more collisions (increase in length in this case) then the resistance increases. The resistance in this investigation is one of the main factors which affects the output of heat so this is one of the main factors which I am going to analyse. The optimum length will be determined on the greatest temperature rise where water will be used to analyse the amount of heat outputted by the 12 lengths of constantan wire. After the practical work I will be also analysing the temperature rise and other factors such as the current, power and voltage as scientific evidence to explain the reasons why the optimum length had the greatest temperature rise.
Planning:
When doing this investigation I will make certain that I will make it a fair test by keeping all the factors constant and remained unchanged, except the factor which is being investigated, which is the length. For example if I were to use 9 volts, I will be using this amount of voltage throughout the entire investigation. However the length of the constantan wire not remain the same since this is the factor I am investigating. In this investigation I will be carrying out 12 tests with different lengths of wires, 300 ml of water, a supply supplying 9 volts and 5 amps, thermometer, plus the output results of the current, voltage, resistance and power. The table on the next page will be used to record my results. The first column shows the length of the constantan wire which will be used. The second column will show the current flowing round the circuit. The third column will show the voltage flowing round the circuit. The fourth column will show the power output of the wires which will have to be calculated by a formulae. And the last column, temperature rise of the water after 5 minutes. Since I am investigating which length of constantan wire outputs the most heat I will keep all factors the same except the length as I want to make this investigation consisting of fair tests. I will be using 12 lengths ranging from 10 cm to 100 cm and from these lengths I will be discovering which outputs the most heat when current is passed.
Testing:
Since this investigation has to go under accurate measurements and precautions before the tests are run, I will run some practise tests. The reason for this is that the figures in my plan may need some corrections such as the setting up of the circuit used to measure and investigate the length. Also investigating the most suitable equipment to see what object or thing I have left out which will be necessary in my investigation. During the investigation, if I see any figures which do not fit with the main pattern or look awkward on a graph I will repeat that result. By the end of the investigation I hopefully find the optimum length of constantan wire which outputs the most heat.
Constantan Wire: This is the resistance wire which will be used in my investigation since it is a resistor and is cheap, hence this is why my science department has bought it. I was hoping to use tungsten wire, although it is expensive and the school has a very limited stock. With this wire which is an alloy of copper (55%) and nickel (45%) I will be investigating which length has the greatest resistance. Before putting the wires in the beaker, they will have to be coiled by being wrapped around a pencil to save volume in the water since it is only 100 ml. I have chosen this alloy since temperature does not affect its resistance in a great way. Therefore when I am investigating its length and if at any time the wire heats up, the temperature will not affect its resistance.
Length: This is the primary factor which is being investigated on to see how the length of constantan wire makes it the best heating element. During my tests I will experiment with the length of constantan to see the most suitable lengths, since some lengths may be too long that they resist so much current that the wire burns, or the length of the wire is so small that it doesn't resist any current at all. I will be testing the 12 lengths from 10 cm to 100 cm since this is a good range to discover the optimum length that makes a piece of constantan wire the best heating element. and after the tests I will know which ten lengths I will be using for the investigation.
Width: The width of constantan wire I am using is is quite thin the diameter being 0.5 cm. I have no particular reason for using such a thin wire. Although I am aware that the width of an insulator affects its resistance.
Voltage: Voltage is one of the factors which affects the resistance of a wire. I will be setting the voltage at 9 volts which I presume is a sensible figure. Since voltage is not the factor I am measuring the amount of voltage inputted into the circuit will remain the same will remain the same throughout the whole investigation, unless I discover during the testing that it needs to be altered.
Current: Current is one of the factors which affects the resistance of the wire. Although I can control the current I will not vary it since I am intending to carry out fair tests, which can be done with a rheostat since current is not the factor I am measuring, but in the future if I was I would have to use one.
I will be setting my power pack which supplies the current and the voltage, at 5 amps which I presume is a sensible figure.
Power: Power is another factor which affects the resistance of a a piece of wire. Its behaviour is linked with the current since if there is less current there is less power.
Supply: A power pack which enables me to control and set a particular voltage and current will be needed. The voltage which will be needed for this investigation is 9 volts on a d.c. current. I am using a d.c. (direct current) current as if I was intending to use a.c. the readings on the ammeter and voltmeter will be vibrating vigorously, hence difficult to record accurate results.
Ammeter: An ammeter will be needed to read the amount of current which is going round the circuit which is affected by the constantan wire. After the current has been measured for a particular length of constantan, with the recorded voltage the resistance and the power output of the wire will be found.
Voltmeter: A voltmeter will be needed to read the amount of volts which is going round the circuit which is affected by the constantan wire. After the voltage has been measured for a particular length of constantan, with the recorded current the resistance and the power output of the wire will be found.
100 ml of Water: This water will be contained in a beaker and will be used to discover the temperature of the wires of constantan. Although it will not directly show me the exact the real temperature of the wire (as it will cool down the wire and the fact the wire has to heat up the water), it will give me an idea of the resistance of the wire. After every test the water will be changed since the last wire would have heated the water up, making it an unfair test if another wire would use the same water. The temperature will be coming directly out of the cold water taps in the laboratory which is approximately 22 C. Although the temperature of the water at the very begging will not be that important since I will be recording the temperature rise of the water, which the constantan wires would have heated up
Thermometer: A thermometer will be used to measure the temperature rise of the water which the wires have heated up, which will show which length of wire is the best heating element producing the most heat. The wire with the lowest temperature rise will be the worst heating element.
Stopwatch: This will be used to time the 5 minutes given for each test where the constantan wire is heating up he water.
Output Results:
Outputted Voltage: Although the voltage supplied by the supply will remain the same, the readings on the voltmeter for the lengths of the wires will not since they are all resisting some voltage at whatever range, since constantan is a metallic insulator. With the outputted voltage the resistance of the particular length of wire will be found and its relationship with the temperature rise will be analysed.
Outputted Current: Again the current supplied by the supply will remain the same, although the readings on the ammeter for the lengths of the wires will not since, again, they are all resisting some current at whatever range, since constantan is an insular. With the outputted current, together with the current the resistance will be found.
Outputted Power: The amount of energy measured in watts supplied by the supply is 40 watts which is found by multiplying the voltage with the current, will remain the same throughout the whole investigation, although the readings on the ammeter and voltmeter will not remain the same since, again, the wires resisting some current and voltage which will affect the power. To calculate the power this formulae will be used:
Resistance: The 12 lengths of the constantan will resist some voltage and current at whatever range, since they are not conductors but metallic insulators. Resistance occurs in a wire or in any element due to its atoms. If the electrons manage to find it difficult to pass through the atoms to get out of the wire then there is resistance since electrons are lost through the collisions of the atoms. The resistance of a wire increases as it gets longer and thicker.
Temperature Rise: The higher the resistance of a particular length the greater the temperature of the wire. By measuring the temperature of the wire by water, it will be the main which will enable me to see if that wire of a particular length is a good heating element. The temperature rise will be calculated by subtracting the original temperature of the water from the temperature of the water five minutes after a test has run, heated by the constantan wire.
Method:
Step 1- Have all equipment ready.
Step 2- Fill 300 ml beaker with 100 ml of water and put thermometer into the water.
Step 3- Cut the particular length of constantan wire you require and then coil neatly round a pencil.
Step 4- Connect the supply, ammeter and constantan coiled wire (with crocodile clips) in a series circuit and the voltmeter in a parallel circuit with the coiled constantan wire.
Step 5- Switch on and set the supply at 9 volts.
Step 6- Check that there is current and voltage flowing round the circuit by checking the ammeter and voltage.
Step 7- When you have checked the circuit begin the stopwatch for 5 minutes.
Step 8- At 4 minutes 50 seconds record the current, voltage, temperature.
Step 9- At 5 minutes switch off the supply.
Step 10- Calculate the resistance and power and record any other results.
The way I have planned my investigation in terms of the factors that are going to analysed, the method I am going to use, the set up of the circuit and the equipment which I am going to use will hopefully result in a successful investigation allowing me to discover whether my predictions are correct and have a deeper insight of the element of constantan and the behaviour of the factors that I am analysing. The reason for this is that I have chosen to do 12 sets of results which is enough to end the investigation with a clear and positive conclusion. Also the way I have designed to set up the circuit is in an appropriate order since I have been aware that certain pieces of equipment should be parallel or series in the circuit and the amount of the current and voltage I am going to use is also suitable for this kind of investigation.
Precautions:
To be certain that this investigation will consist of fair tests, I will measure the lengths of the constantan wire with precision. When I am putting the constantan wire into the water I will make sure that I avoid the crocodile clips having contact since there will be a short circuit which will interrupt my test. When calculating the temperature rise I will record the waters original temperature so the temperature rise which is needed will be accurate. If I suspect that there are any incorrect results I will repeat that test. I will make sure that I will be using the same supply and to keep it at 9 volts at all times and the current at 5 amps. I will be using a wide range ammeter and voltmeter since some lengths of constantan will not resist enough current or voltage that other metres will not be capable of representing the figures. Although I must take into account that the readings will not be as accurate, but this accuracy difference is very small. The amount of water in the water will always remain 100 ml so that different lengths of wires do not have to heat different amounts of water which will make it an unfair test. Also I will not be using the same piece of constantan wire for more that one experiment, since after one the piece of wire looses some of its mass, width and length, all affecting its resistance. When placing the thermometer into the beaker I will make sure that there is no contact between the thermometer and wire since the thermometer would be measuring the temperature of the wire not the water, which again would make it an unfair test. The time given for the lengths of constantan wire will remain the same at all times through the test, a time of 5 minutes. I will also be using the same thickness of constantan wire throughout the whole investigation. When calculating the figures of resistance and power I will use a calculator to ensure there are no errors in them. I will also make certain that i handle all the equipment well with great care in order to produce reliable results, and to treat all school equipment with great respect in order to avoid any electrical or physical accidents.
Prediction:
I predict that that the longer the piece of constantan wire the higher the resistance therefore the smaller the current. This is because the constantan wire heats up when current is passed through. Electrons, subjected to a force because of an electric field, accelerate and progressively acquire greater speed. Their velocity is, however limited in a wire because they lose some of their acquired energy to the wire in collisions with atoms in the wire. The lost energy is either transferred to other electrons, which later radiate, or the wire becomes excited with tiny mechanical vibrations referred to as phonos and both processes heat the material. Also the longer the piece of constantan wire, there are more atoms. As there are more atoms to collide with therefore more heat is produced. Therefore the longer the piece of wire the more heat is produced the higher the temperature of the water, hence the better a heating element, and the smaller the piece of constantan wire the lower the resistance, collisions are less therefore the poorer the heating element
I also predict that the voltage of the constantan wire decreases with the current as the constantan wire gets longer, since both of these factors are directly proportional.
I also predict that the power will decrease as the resistance of the constantan wire increases. This is simply explained that one of the ways in calculating the power is to multiply the current together with the voltage. If these two factors decrease then the power must also decrease.
Earlier Work:
I have done some earlier work during year nine where we had a short experiment testing how the material of the wire affects the resistance. Although there was no advanced scientific explanation involved.
By Heresh Rezavandi
After 10 successful tests had been completed I plotted them on a table:
According to my results my prediction in stating that the longer the piece of wire the higher the temperature rise was wrong. In fact the complete opposite occurred where the temperature rise actually decreased as the length of the wire increased. The graph labelled "Temperature Rise After 5 mins. (C) Against Length of Wire (cm)", shows the pattern of the temperature rise against the length of wire is vaguely inproportional, so I have not drawn a best fit line but a best fit curve. The reason for this is that from lengths of 25 cm to 50 cm there is a slight curve and it is only from 60 cm that there is a straight line. To prove that the temperature rise is inversely proportional to the length of the wire I have created another graph where instead of plotting the length of the wire on the x axis, I have used the formula 1 / Length. After the graph was created the graph labelled "Temperature Rise After 5 mins. (C) Against 1 / Length" proves that the temperature rise is inversely proportional to the length since the points are around a best fit line. I also worked out the gradient of this graph being 0.66 showing how rapidly the temperature rise increases as the 1/length increases, indicating how rapidly the temperature increases as the length increases.
My prediction in stating that the resistance of the constantan wire increased as its length got longer was correct. The graph labelled "Resistance (ohms) Against length of Wire (cm)", shows the pattern of positive colleration between the resistance and the length of wire since all points are on or very near the best fit line. I also worked out the gradient of this graph being 0.454 showing how rapidly the resistance increases as the length increases.
My prediction in stating that the current decreased as the length of the wire increased was correct. The graph labelled "Current (amps) Against length of Wire (cm)" shows the pattern between current and the length of the wire is inversely proportional since all points are on or very near the best fit line. The gradient of the graph is -0.33 showing how rapidly the current decreases as the length increases.
My prediction in stating that the power decreased as the length of the wire increased was also correct. The graph labelled "Power (watts) Against Length of Wire (cm)" shows the pattern between the power and the length of the wire is inversely proportional since all points are on or very near the best fit line. The gradient of the graph is -0.25 showing that the decrease of power as the length increases is less rapidly than the other factors. Also the pattern of this graph is very similar to the current, since the power is calculated by the current multiplied by the voltage. If the current decreases then the power must also decrease even though the voltage increased it was not enough as the voltage only increased from 6.4 volts to 7.8 volts where the current decreased from 5.4 amps to 1.5 amps. It is also similar to the temperature rise since if there is less current there is less power meaning there is more resistance meaning the temperature rise decreases with the power.
My prediction in stating that the voltage decreased as the length of the wire increased was also incorrect as it actually increased as the length of the wire increased. In this graph I am unable to draw a best fit line so i have drawn a best fit curve. The voltage acted strangely in my investigation since it rapidly increased at the points of 25 cm to 40 cm and then began to increase to 100 cm very slowly.
Conclusion:
According to my results some of the predictions I made about this investigation was wrong, although some were proven true. I predicted that the longer the piece of wire the higher the resistance, due to the fact that there are more atoms in longer wires meaning more electrons are lost, therefore less current. This was proven by the fact that the longest length of constantan wire I tested, 100 cm, had the greatest resistance at 5 ohms and the shortest length, 20 cm, had a resistance of 1.185 ohms.
I also predicted that the higher the resistance the higher the temperature rise of the water since in longer wires there are more atoms for the electrons to collide with, therefore more heat is produced. This was proven incorrect as at 100 cm its temperature rise was the least with a mere 9 C, whereas the shortest length of 25 cm the temperature rise was 28 C. Although the prediction that the longer the length the higher the temperature rise is true to an extent, unless the same amount of current has to be circulating around the circuit with the wires of constantan. In order for this the current has to be increased as the length of the increases. Since the same amount of current was being used for every length of constantan, the longer pieces of constantan wire resisted more current, therefore the temperature rise of the water heated by the longer pieces of wire was less. Hence the smaller the piece of wire the less it resists, the more the current therefore the better the heating element. Encyclopaedia Britannica
Surprisingly my prediction that the voltage was directly proportional to the current actually increased as the current decreased which indicates that in this case the two factors are indirectly proportional. The resistance being present in the wire is responsible in the circuit has caused the voltage to act in this way.
My prediction in stating that the power would decrease as the length of the constantan wire increased was correct. The reason for this is that the power is directly proportional to the current. If there is less current then there is less power, meaning there is a less energy output. This explains the reason why the temperature of the water decreased as the length of the constantan wire increased.
Although the voltage increased which could have affected the amount of power, it was not enough as the voltage only increased from 6.4 volts to 7.8 volts where the current decreased from 5.4 amps to 1.5 amps.
I put into account that the temperature rise of the water increases the resistance of a wire, which meant the graphs would not have been a straight line but a curved one due to the rapid decreases of resistance towards the longer pieces of wire. At the end of my investigation I saw that this did not occur in my investigation realising that I had been using constantan wire which is a rare element which its resistance is hardly affected by temperature.
By Heresh Rezavandi
The investigation was a success enabling me to discover the best length of constantan which makes it the best heating element. There were clear patterns in the set of results which were accurate enough to come up with a clear conclusion, which were expected as I predicted correctly, such as the resistance of the constantan wire increasing with the longer the length, the current decreasing the longer the length and the power decreasing the longer the length. The two other sets of results which proved part of my prediction wrong was the behaviour of the temperature rise and the voltage.
The reason why the investigation went so well is that the method I used was suitable and accurate for finding the resistance of the 10 lengths of constantan wire. I had the circuit set up in the correct manner meaning I made certain that the voltmeter was in a parallel circuit with the constantan wire, the ammeter in series with the constantan wire, and the supply also in series with the constantan wire and always at 12 volts. I also made sure that the length of the constantan wire I was going to use was measured accurately. I also made sure that the water which the constantan wires were going to heat up was always at 100 ml and always recorded the original temperature of the water. The thermometer which was used to measure the temperature of the water never made contact with the constantan wire meaning it was always measuring the temperature of the water and the not the piece of wire which made it a fair test.
Fortunately there was only one result that did not fit in the main pattern and that was at 40 cm of constantan wire. I was aware of this since its current, voltage, resistance, power and temperature rise were reversing direction of the pattern they were suppose to go in. The reason for this is that I may have measured the length wrong or the supply was at 14 volts. Any of these two factors could have occurred. At 20 cm I was unable to discover the temperature rise since the supply kept on short circuiting since at this length very little current was being resisted. So I did decided to not to test the lengths of 10 cm and 15 cm, although I am quite sure that there temperature rise will be higher than the highest temperature result of 25 cm which raised the temperature of the water by 28 C, if there wasn't a device in the power-pack which enabled it to short-circuit. As a result I had 10 full results and one unfinished with the reasons explained.
I had enough correct results to draw a conclusion since I had 10 accurate results which were enough to reveal the behaviour of the five factors I was measuring. Only two results (10 cm and 15cm) could not be found due to the power-pack short-circuiting at high currents and one result (20cm) which I was only unable to discover its temperature rise. With these results the optimum length at these lengths for the best heating element was found and the worst heating element at these lengths was also found.
The investigation could have been improved if I had used a power-pack which did not short-circuit (even though it was for the users own safety) during the testing of the short wires, meaning I would have had more results. The accuracy of finding out the resistance of the wires could have been improved if the ammeter and the voltmeter was more accurate, even though they were accurate to a certain point to output good results. Using a more accurate thermometer could have improved results, again even though it was accurate to a certain point to output good results. The size of the crocodile clips which were used to hold the lengths of constantan wire were a bit too large which meant they caused trouble by making contact with the constantan wire, especially with the long lengths, resulting in a unusually high temperature rise. When the crocodile clips made contact the circuit short-circuited, meaning time was wasted to wait until the power-pack reset. If the school provided smaller crocodile clips then the investigation could have been easier to accomplish. To have used a more sophisticated circuit and equipment could have outputted better result.
To add and investigate further factors which make a piece of wire the best heating element, to improve my investigation, I could have investigated the width to discover whether a thick or thin wire has a greater resistance. The material of a wire also greatly affects the resistance. A copper wire has a much lower resistance that constantan for which is why it used in wires. The temperature surrounding a piece of wire also affects its resistance as the higher the temperature of the wire gets the higher the resistance. I could investigate the reasons why this happens. The amount of current, voltage and power also affects the resistance of a piece of wire.
During the investigation I discovered another formula for calculating the power:
When I used this formula to calculate the power of my set of results I saw that the figures were very similar to my original formula of:
Therefore I decided to ignore the new formula.