Energy= Volts x Columbs
Calculating thickness of wire:
As it is difficult to find the thickness of one strand of wire without an advanced piece of equipment. I will find the length of 100 wires and divide it by 100.
Circuits in series and parallel:
Series – Chain Link:
The Total resistance= R1+R2+R3
(RT)
The total length resistance=L1+L2+L3
(LT)
Parallel- Ladder form:
RT= Product / Sum
=
Each wire acts as a resistor.
Factors affecting outcome
The independent variables (The factors that can be changed)
- Length of wire
- Thickness of wire
- The temperature
- Pressure/ tension
- Gravity
- Current
- Voltage
The dependent variable (variable I will measure):
Key variables:
- Length
- Area
- Resistance
- Voltage/current
This overview basically means that resistance is the only thing that is only dependable to change when these (independent variables) factors are changed. The (independent) variables which I will keep the same will be the;
- Temperature
- The pressure,
- Tension of the wire,
- Gravity and the light.
Length and thickness will be the test.
Safety:
I have to make sure that the experiment is conducted in an area away from any water as it is a good conductor and as I am using electrical equipment it could be potentially harmful.
Prediction
I predict that as the length of wire decreases so will
the resistance because there are less metal atoms in the wire which will provide resistance, and if the length increases so will the resistance because there are more metal atoms to collide with. Ohms law will be used to solve the resistance for each length of wire. So, if we double the length of a wire, the number of atoms in the wire doubles. I predict that if the length of wire doubles so will the resistance.
I also predict that if the cross sectional area of the wire increases the resistance will decrease. This is because if the electrons have more room to go through the wire there will be less collisions and therefore less resistance.
- Length up = Resistance up
- Thickness up = Resistance down
Direct Method and Fair testing
I am going to set up a circuit which will consist of a
length of nichrome which will be the only variable (other than thickness), a power supply which will only provide 2 volts for safety, an ammeter to measure the current in amps, a voltmeter to measure the voltage in volts and a variable resistor to break down the voltage for safety. The length of
wire will be measured carefully against a metre ruler and 50cm
measured. The investigation will be started with 10cm and will be
measured with a 30cm ruler. The 10cm of wire will be placed between
two crocodile clips which will be connected to the circuit with
connecting wires. Each measurement will be straightened and measured over in accurate steps to make the investigation as fair as possible. For each length the voltage and the current will be noted. I will try to keep the temperature constant by keeping it in the same place and making sure it receives the same amount of sunlight. Also I am going to keep the temperature constant by not increasing the voltage throughout the experiment. I will the repeat the experiment to increase the validity of the results and prove the pattern stays the same that as the length of the wire increases so does the resistance
R= Ruler with nichrome wire
Ohmmeter
Results Table- thickness vs. length
Indirect method:
First I will attach my piece of nichrome wire to a meter ruler. I will then take a voltmeter and ammeter and wire them up as you see in the diagram below. Next I will attach crocodile clips to the ends of my circuit wire and attach them to the nichrome wire. I will then measure the voltage and current of the nichrome wire. I will measure a 10cm piece of nichrome wire, then 20cm, and I will continue this up to 100cm.
(V)= voltmeter
(A)= Ammeter
R= Ruler
Results Table- Voltage vs. current
Calculating thickness of wire
I worked out the thickness of one wire by getting the thickness of 100 wires and then dividing that number by 100
Total thickness of 100 wires (coils) = 3.7cm
Thickness of 1 wire = thickness of 100 wires ÷ 100
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Safety measures:
- I made sure there is no water or liquid near my workstation as I am working with electricity.
- I made sure my workstation is clear and organised.
- I made sure that my schoolbag is under the desk and out of the way
List of apparatus:
- Nichrome wire
- Ohm meter
- Power source
- Crocodile clips
- Circuit wires
- Meter ruler
Direct Method and Fair testing
I set up a circuit that consisted of a length of nichrome which was the only variable (other than thickness), a power supply which only provided 2 volts for safety, an ammeter that measured the current in amps, a voltmeter that measured the voltage in volts and a variable resistor that broke down the voltage for safety. The length of
wire was measured carefully against a metre ruler and 50cm
measured. The investigation started with 10cm was
measured with a 30cm ruler. The 10cm of wire was placed between
two crocodile clips which connected to the circuit with
connecting wires. Each measurement was straightened and measured over in accurate steps to make the investigation as fair as possible. For each length the voltage and the current was noted. I tried to keep the temperature constant by keeping it in the same place and making sure it received the same amount of sunlight.
Also I kept the temperature constant by not increasing the voltage throughout the experiment. I repeated the experiment to increase the validity of the results and prove the pattern stays the same that as the length of the wire increases so does the resistance. I made sure that the experiment is conducted in an area away from any water as it is a good conductor and as I was using electrical equipment it could have been potentially harmful.
Results Table
Resistances of a Length of nichrome wire L = 100cm for different thicknesses
Indirect method:
First I attached my piece of nichrome wire to a meter ruler. I then took a voltmeter and ammeter and wired them up as you see in the diagram below. Next I attached crocodile clips to the ends of my circuit wire and attached them to the nichrome wire. I then measured the voltage and current of the nichrome wire. I measured a 10cm piece of nichrome wire, then 20cm, and I continued this up to 100cm.
Results table
Analysis
R = K x L/A
K= Slope value (slope x area)
Slope = Rise/Run
Slope= 4.9/0.5 = 9.8
Area= 11.34 x 10(to the power of) -8
K= 11.34 x10 (to the power of) -8 x 9.8 =111.132x10 (to the power of) -8
From this table I obtained from
I can say that the nichrome wire results they obtained and the results I obtained are very similar.
Conclusion
Looking at the graph results when using the direct method for investigating the physical quantities and seeing how they affect the resistance of the sample of nichrome wire, the outcome was as follows.
For a variety of thicknesses from 1x to 5x, and using fixed length of 1(m), the resistance was recorded at each 10cm step from 0 to 100cm. The results turned out to be arranged in or extended along a straight line for all the graphs, making the slope smaller as the thickness gets greater. This was further re-enforced by plotting the graph of Resistance v Thickness which shows a curve line with resistance going to infinity (∞) as thickness goes smaller and smaller.
This turned out to agree with my prediction that I first made in my Planning stage. The straight line linear parts of the set of graphs drawn also seem to agree with my prediction for change in resistance with changing length.
However, in close inspection, it is seen that the graphs all begin at a value of about 0.7(Ω) and not at the origin as expected. I was surprised at this out come. This seems to disagree with the statement in my plan at the beginning for the graphs R v L which predicts the graphs should go through the origin. In order to try and explain this unusual result I proceeded to go back and set up the investigation again using the ohm-meter and only using both connecting leads connected together and then only one plugged into the meter.
This now shows quite clearly that the built in resistance of the actual connecting leads have a total resistance of 0.6Ω and 0.35Ω for a single lead.
So on final analysis of these results, I can now say that my graphs do agree with my first prediction. I then proceeded to carried out the investigation, using the electrical quantities to calculate resistance of different lengths of wire by using Ohm’s law. This is known as the indirect method and only one thickness was looked at as it was only to compare with the accuracy of the result obtained by the direct method.
In being aware of the possibility of the wire heating up if too high a voltage is used it was decided to keep the supply voltage fixed at 2V. In doing so it keeps the range of reading to be very small. It was also suggested to not take any readings less than a length of 20cm. as the resistance would be too small and it may allow the wire to heating up and give non-linear results. It was also decided to switch off the power supply when readings were not actually been recorded on the ammeter and voltmeter. This again was to avoid any overheating by current passing through the nichrome wire.In this method the results obtained from the graph was a straight line going through the origin as predicted in my plan.
In each method the slope of the graph was measured by selecting a reference point and measuring the Rise over the RUN to determine the gradient of the slope. From this value it can be shown how the K-factor of the nichrome wire can be calculated from the analysis below and this value compared with a reference known value obtained from researching on the WEB or a Physics text book.
Evaluation
Working on the experiment has overall been an interesting and knowledgeable task. From obtaining the result that has matched my prediction, I can say that my background knowledge on the steps of the procedure was adequate. I am glad with how the experiment has been observed, studied and recorded for future use of physicists.