GRAPH FOR FINAL RESULTS ON VOLTAGE - 5W AND 24W FILAMENT BULBS
Conclusion for Final Plan -
Voltage -
From the analysis of both results I can see that once the voltage is increased the current increased alongside. From using the formula R = V / I, I can see that the resistance increased once I had increased the voltage. This shows that the voltage flowing through a light bulb affects the resistance. I believe this is because the filament of the 5W bulb is much thinner than the filament of the 24W bulb which is much thicker. This may be because less electrical current can flow through a thinner filament, meaning fewer electrons can pass through and there is more resistance. I decided to conduct a further investigation to see to which extent the thickness, temperature, type of filament and length of filament affects the resistance.
From my graph I can see that resistance of the 24W filament bulb is much lower than the resistance of the 5W bulb. From looking at the curve of the graph I can see a significant difference in resistance between both bulbs. I believe this is due to the difference in thickness and length between both filaments. I believe the filament of the 24W bulb is larger in length and has a larger thickness. This has caused it to have a lower resistance as with a smaller area of filament fewer electrons will be able to pass through, which decreases the amount of current. I also believe that difference of resistance of both light bulbs may be due to a difference of lengths of the filament. Another factor which I believe could have made a difference is the material of the filament. In my extension investigation I have decided to investigate these factors as well. Also from looking at the graph I can see a steep rise in the curve of both filament bulbs, from the range of 0 to 1 volts. I believe the increased gradient is because of the sudden increase in temperature of the filament once it starts to get hotter. I believe this is another factor that could affect the resistance of light bulbs, so have decided to investigate this factor in my extension investigation. In conclusion from my results and tables I can see that as I had increased the voltage the resistance increased. This is because voltage is directly proportional to the resistance. I can see this through the Ohms Law Triangle which shows ‘R = V / I’. I can see the rise in voltage from looking at the 24W bulb. With a supply of 5.02V the resistance is 4.08Ω whereas with a supply of 10.04V the resistance is 5.84Ω. This clearly shows that once the voltage increases the resistance also increases. This proves that as the voltage increase, the resistance also increases proportionally.
Extension Investigation -
To complete the investigation I will need an independent and dependant variable. The independent variable is the variable that I will be changing throughout my investigation, which will help me in investigating the resistance of light bulbs. As my independent variables I have chosen are the voltage, thickness, length and material. I will also need a dependant variable, which is the variable I will be measuring. As my dependant variables I have chosen the voltage and current - which I then used to calculate the resistance. To complete the investigation fairly and accurately I will need to keep other variables in control, which are known as my control variable. My controls variables are the length, material and thickness of the wires - these will help me complete the investigation fairly.
As all filament light bulbs contain a wire strip in them I had decided to investigate how the length of wire, the type of wire, the cross sectional area (thickness) of the wire and temperature affects the resistance of light bulbs.
Firstly to investigate length I have decided to use different length wires to see how the length affects the resistance. I have chosen to use different lengths of constantan as this is the most common type of filament used in light bulbs. I have decided to investigate the length ranging from 0.2m to 1.0m, increasing by 0.2m each experiment. In this experiment I will be connected an ammeter in the circuit and will also be connecting a voltmeter in parallel to the different length wires. The ammeter and voltmeter will help me measure the voltage and current, this can then be used to find the resistance of the wire, which can be present inside a filament light bulb. During the investigation I will be keeping the type of wire used and thickness the same - using constantan with 24SWG thickness. This will help me complete the experiments fairly.
Secondly I have also decided to investigate how the type of filament wire affects the resistance of light bulbs. I have decided to use different types of wire, while controlling the length and voltage. The different types of wire that I will be using are constantan, manganin and nichrome. By using different types of wire present in light bulb filaments I can see how difference in material of filaments affects the resistance of light bulbs. During the experiment I had to keep some factors in control. The factors that I will control are the thickness and length of the wire, keeping the wire at 0.6m length and at 24SWG.
Additionally I have decided that I will be investigating how the difference in cross sectional area of filaments affects the resistance of light bulbs. To complete this investigation I will be using different thicknesses of constantan. I have chosen to use constantan because it is the most common material used as filaments in light bulbs. During the investigation I will be keeping the length of wire – 0.2m and the material of the wire the same - constantan. This will help me conduct a fair experiment allowing me to come to an accurate conclusion.
Finally I have decided to investigate how the temperature of the light bulb affects the resistance. I have placed the filament submerged under water so all the heat energy will be absorbed - keeping the filament at a constant temperature. I have used a 24W bulb and have measured the voltage and current at different stages.
Equipment List -
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Filament Light Bulb - To test the resistance of the light bulb
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Connectors - To connect the circuit together
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Crocodile Clips - To connect the different types of wires to the circuit.
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Power Supply - To power the circuit so the resistance can be calculated
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Rheostat - A variable resistor so the voltage can be altered
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Digital Ammeter - So the current flowing through the circuit can be measured
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Digital Voltmeter - So the voltage flowing through the circuit can be measured
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Constantan, Manganin and Nichrome Wire - So I can investigate how different material filaments affect the resistance of light bulbs
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Beaker and Water - So the temperature can be measured as the filament is submerged under water
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Ruler - To measure the amounts of wire
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Wire Cutters - To cut the different length wires
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Micrometer - So the width of the wire can be measured.
Method (Main Setup) -
To complete the investigation I need a clear method to tell me how to do the experiments. Below I have written a method to show how to complete the experiments needed for the investigation:
- Collect and arrange equipment
- Connect Power Supply and add connectors from the DC current.
- Connect a digital ammeter and a rheostat to each end of the wire.
- Add a connector to the end of the digital ammeter and the rheostat.
Method (Type of Wire) -
5) Add crocodile clips to the end of the connectors.
6) Collect the different material wires of exact thickness and all cut to the
same length.
7) Attach the different material wires to the end of the crocodile clip.
8) In parallel connect a digital voltmeter over the different material wire.
9) Switch on power supply and measure voltage and current.
Method (Length of Wire) -
5) Add crocodile clips to the end of the connectors.
6) Cut constantan wire of same thickness to different lengths.
7) Attach the wire to end of crocodile clips.
8) In parallel connect a digital voltmeter over the length of constantan wire.
9) Switch on power supply and measure voltage and current.
Method (Area of Wire)
5) Add crocodile clips to the end of the wires.
6) Collect constantan wire of different thickness but and cut to same length.
7) Attach wire to end of crocodile clips.
8) In parallel connect a digital voltmeter over the length of constantan wire.
9) Switch on power supply and measure voltage and current.
Method (Temperature)
5) Fill up a beaker with water.
6) Connect a 24W Filament Bulb to the end of the connecters.
7) In parallel connect a digital voltmeter over the bulb.
8) Submerge the bulb under water.
9) Switch on power supply and measure voltage and current.
Final Table of Results for Extension Investigation -
Type of Wire (Material) -
Length of Wire -
Area of Wire -
Temperature -
GRAPH FOR TYPE OF WIRE (MATERIAL)
GRAPH FOR LENGTH
GRAPH FOR LENGTH (GRADIENT)
GRAPH FOR AREA OF WIRE (THICKNESS)
GRAPH FOR TEMPERATURE
GRAPH FOR TEMPERATURE (GRADIENT)
Conclusion for Extension Investigation -
Type of Wire (Material) -
From investigating the type of wire I can see that different material wire have different resistivity. Constantan and manganin are two similar type of filament wire as they have less resistance than nichrome, which has a very high resistance. I can see this from my graph and tables as the average resistance for constantan is 1.29Ω and for manganin it is 1.26Ω. The resistance of nichrome is much higher, averaging 8.64Ω. From this I can see that different filament material affect the resistivity of light bulbs. This is because each metal alloy has different rates of conductivity as they have different properties. As their rates of conductivity are different their resistivity also varies which is shown as nichrome has a much higher resistance than the other types of filament wire. Usually the resistivity is determined by the atomic structure of the elements. This affects the resistance as if the electrons are tightly packed, the resistivity increases as the current flowing through the circuit is limited. Additionally the number of free electrons per metre cubed (m3) affects the resistance. If a material has a higher number of free electrons it means that it is easier for current to flow through. This means that the material is a good conductor and has a low resistivity - which in my results is shown by the materials constantan and manganin. However in comparison, if a material has a low number of free electrons it means that there is less chance of current flowing through the circuit. This means that the material is a good insulator and has a high resistivity, as seen with nichrome. I have also worked out the resistivity of the different material of filament. An example of the formula and my calculations is shown below:
…in standard form
From the table showing the resistivity of different materials I can see that constantan and manganin roughly have the same resistivity. In comparison to nichrome, constantan and manganin have a very high resistivity. This was because the electrons in nichrome are tightly packed together, which means the resistance is clearly higher.
Length of Wire -
From investigating the length of wire I can see that once the length increased the resistance also increased. In the analysis of particular points on the graph, the average resistance at 0.2m is 0.38Ω, 0.4m is 0.83Ω, 0.6m is 1.25Ω, 0.8m is 1.70Ω and 1.0m is 2.14Ω. This clearly shows that once the length of filament is increased the resistance also increases. As the length increases, electrons have to travel a further distance. As they travel further, the resistance increases which is shown from my results. Also as the electrons have to travel a further distance they will face many more collisions. Resistance occurs as a result of collisions between electrons and atoms in the wire. This shows that the further the distance travelled the more collisions meaning a greater resistance. This shows that as length increases the resistance also increases proportionally. Additionally from my graph my line of best fit has produced a straight line. This shows to me that the length is directly proportional to the resistance. I have worked out the gradient using the following formula which will show me the ohms per metre:
The formula showed me the amount of resistance per metre of wire. From looking at the line of the gradient I can see that as the length of wire increases the resistance of the wire also increases. Also from the gradient calculations I can see that from my line, at three of the four points the gradient is 2.08Ω. This proves that resistance is directly proportional to length.
Area of Wire (Thickness) -
From investigating the area I can see that as the cross sectional area of the wire increased the resistance decreased. I decided to calculate the cross sectional area rather than the SWG because the SWG is not a figure and conclusions made of SWG may be inaccurate and not in detail. I had calculated the cross sectional area by finding the width of the piece of wire. I had found this out using a micrometer, which accurately gave me the diameter of wire to four decimal places. Using simple mathematics I had calculated the cross sectional area. An example of my calculations is shown below:
22SWG -
Diameter = d = 0.7112mm
Radius = r = ½d = 0.397259mm
Cross Sectional Area = πr3 = π0.35563 = 0.397mm
By working out the cross sectional area it is easier to plot on the graph and shows me a clear curve. From the graph I can see that as the area of the wire increases the resistance decreases. This is shown through an exponential curve. I believe that the thicker filament had less resistance because more electrons could pass through due to the larger diameter. In comparison the thinner wire had more resistance because fewer electrons could pass through due to the limited space. The curve shows that no matter how long or short the wire is there will always be some resistance. This is shown through the curve which shows that with infinite amount of wire there will be at least some resistance.
Temperature -
From investigating the temperature I can see that once the temperature was kept constant the resistance also stayed the same. From looking at my results for voltage I can see that the graph produced a straight line. Also there was a high curve between 0 and 1 volt. This suggests that temperature makes a difference - this is because during the rise in voltage the filament heat up a lot which increases its resistance. By keeping the filament bulb under water, the water particles absorb all the heat which is released as the current flows through the bulb. In comparison, in a normal filament wire if the temperature increases the electrons vibrate more vigorously and move around more. This means that there are more collisions between the electrons and the particles inside the wire. As there are more collisions it means that the resistance is higher. This shows that under a constant temperature the resistance stays the same. This proves that temperature affects the resistance of light bulbs, as once the temperature of the filament increases the resistance increases. From looking at the table and looking at the results I can see that as the wattage increases, while kept under a constant temperature the resistance stays the same. I have used the formula to find out two different wattages of readings: ‘P = V x I’, I have calculated three different wattages which are 10.23W, 19.93W and 27.84W. At all these wattages the resistance of the light bulb is equal which again proves that temperature affects resistance, as if the temperature is constant, the resistance is also constant, whereas if the temperature increases the resistance also increases. I have also calculated the gradient of the line of best fit for the bulb when kept under a constant temperature. I have worked out the gradient using the following formula which shows me the amount of ohms per meter:
By working out the gradient, I can see that all the gradients calculated show a resistance of 0.67Ω.This proves that as the temperature of the filament is constant the resistance also stays the same. From this I can conclude that temperature does affect the resistance of light bulbs, as if the temperature is constant the resistance is the same, and if the temperature increases the resistance increases. Also from analysing the graph I can see that after 4V, the results started to curve. This may have been because the water could not absorb any more heat energy, meaning that the filament started to heat up. This may have caused the slight rise in resistance after 4V.
Overall Conclusion -
In conclusion from the data I can see that the as the voltage increased the resistance also increased. I can also conclude that different materials affect resistance as they are made up of different properties. Additionally the length affects resistance because as the length increases the resistance also increases. From this I can see that length is directly proportional to resistance. I can also see that as the area of wire increases the resistance decrease. Finally I have found out that the temperature affects resistance as if the temperature is kept constant resistance also stays the same. In total I can see that there are five factors which affect resistance which are described above.
Evaluation -
I believe that I have completed the investigation to a very high standard. I think that all the results I have collected are accurate and I have drawn precise conclusions. There are also some improvements that I could make, and these are shown below.
I have used a variety of accurate equipment while conducting the investigation. I had used accurate apparatus such as a digital voltmeter and ammeter, a rheostat (variable resistor) and a micrometre. There are also some improvements that I could make to the equipment that I used. Firstly in all my experiment the reading on the digital ammeter and voltmeter kept on varying due to the high levels of accuracy. Although this gave me highly accurate readings there was slight inaccuracy as the reading varied and no selective reading could be noted. If I was to complete the investigation again I would use an analogue ammeter and voltmeter which went to an accuracy of a hundredth of an ampere and volt. This would ensure that the reading would not vary, enabling me to collect highly accurate results which could be used to make precise conclusions. One other price of equipment that could be changed is the power supply. If a high quality power supply was used it would mean that the voltage released by the source would be accurate to the reading on the dial, which can help save time and calculate resistance for particular voltages. Another change that I would make is to use a more accurate measurer to find the width of the different SWG wires. Instead of using a micrometer I would use a nanometre which would measure the width to a higher level of accuracy, meaning that the graph that I create would show an accurate pattern, and the formulas I completed would be to great detail. Also while investigating temperature there were many variances in my results. After around 4.5V the line started to curve. I believe this is because at this point the water started to heat up. I had noticed this during the experiment as I started to hear water boiling. As the water started boil and give me inaccurate results, which I would improve by conducting more of the same improvements. I would also complete the same investigation of temperature, but use iced water instead of water and room temperature. By using iced water, more of the heat energy is likely to be absorbed, which will help keep the filament at a constant temperature of roughly 0°C. Also I could place the bulb in a water bath at a constant temperature. These methods would ensure that I would not get anomalous results and the conclusions that I would draw would be accurate.
During my investigation I believe that the results collected are accurate as all my results collate to fit with a general trend. There are two sets of anomalous results, one for my preliminary results and the other for my results on how temperature affects resistance. Once I had experienced the outliers with the preliminary results I had made all necessary changes which guaranteed that there were no more outliers in my further experiments. Additionally I had faced a few problems with the temperature. I had got many outlier results which I believe was because the water did not absorb the heat energy effectively. Once the water had been heated, the heat energy stayed with the filament, causing the resistivity to rise, meaning that my results were inaccurate. To ensure that I would not have any outliers I would repeat the experiment and also keep the temperature constant by the use of different substances.
To evaluate my results I have also used mathematical formulas such as gradient calculations and the resistivity formula. The mathematical data, alongside my results help me prove that the data I have collected is reliable which ensures that the conclusions I have made are correct. Also from the analysis of the graphs with range bars I can see that they are relatively low. For my results on length, the highest range is 0.11 and it is the same for area. This suggests that the results I have corrected are relatively accurate and precise.
All the factors above show that I have collected reliable and accurate data, which I have used to make valid conclusions. The main improvement that I would make would be that if more time was given, I would repeat the experiment to make secure conclusions. Overall I believe that I have completed the investigation to a high standard and have collected enough reliable data to come to accurate and precise conclusions.