My Perlimary Investigation
Before I did my main investigation I decided to do a perlimary investigation to find the values I will use for the length of the wire. I found the resistance by using R=V/I with different lengths of wire, from this I was able to choose my results for the main experiment.
This is the circuit used.
The different lengths of wire. I found the resistance by taking readings of the voltage and current, and the resistance was 1 to 3.7. I decided to use these lengths for my main investigation because it gave me a good graph.
I predict that as I increase the length of the wire the resistance will also increase in the circuit.
Theory
I got this information from ‘
Resistance is based around the idea of ohms law, which states
“The electrical is a given conductor is directly proportional to the potential difference applied, provided that the temperature of the conductor and its other physical factors remain constant”.
This means that when the temperature of the wire is constant and the voltage is varied along the wire and the current may be lower. Resistance is represented by the symbol Ω which is the great letter omega = ohm.
The amount of resistance varies from small values to bigger values depending on the appliance. A copper wire for example is measured in a resistance of 1/100 Ω where as something like a radio or a T.V has that of millions of Ohms. Engineers have thought up fundamental formulas for calculating Current, Voltage, and Resistance.
Resistance = Voltage
Current
OR I = V OR V = I * R
R
These are how the resistance of a wire/circuit/appliance are measured or vice versa, by using the definition R = V/I. This is the formula I will be using in the investigation.
In my science investigation I am investigating length of wire, the things I will keep the same are the thickness of the wire, the temperature of the wire. By doing these I will make my investigation fair. The thickness of the wire I will be using will be: 13457 cm. The temperature I will be using is room temperature.
The equipment I will be using is as follows:
Method
In my experiment I am going to pass current a piece of resistance wire to find what resistance the wire has on the circuit.
To find the resistance I will be using ohms law and the formula
R = V/I dividing voltage by current readings from the circuit.
To guarantee accuracy I will repeat the experiment 3 times to get the most accurate readings so there are no bad readings.
To keep my experiment safe I am going to turn off the power pack each time I increase the length of the resistance wire and use a low current to reduce the heating effect. This also means that if someone accidentally touches the wire they won’t burn themselves.
Results
During the experiment I recorded the results and I also observed what happened. At each length measurement of wire, when the current increased, so did the voltage which is what I expected. I repeated each Length interval three times to get three sets of results. I did this to work out an average which meant that I have produced more accurate results.
In my investigation I took readings of the voltage and the current. I then used the formula R=V/I to work out the resistance for each length of wire. Looking at the results I obtained I would say that they are accurate and there are no anomalies. As the length of the wire increased I saw that so did the resistance of the circuit. I also noticed the heating effect, but because I used small currents it didn’t affect the accuracy of my results too much.
Analysis
I plotted the resistance against the length of the wire and then drew a line of best fit. As you can see from the graph there are no anomalies because the points are so close to the line. The graph proves that my prediction was correct. I predicted that the longer the wire, the higher the current and this is shown by the graph. As the length increases so does the resistance. For example at 10 cm the resistance was 0.30 Ω and at 20 cm the resistance was 0.65 Ω. The gradient of the graph is 0.35. The formula for the graph is Y = 0.35 x X + 0.90 or to work out the resistance of any length; Resistance = 0.35 x Length of Wire + 0.90.
I also predicted that if I double the length of wire the resistance would double because there are twice as many atoms for the electrons to pass. From the results I obtained my second prediction was nearly correct. For example from 10 cm to 20 cm the resistance was 0.30 Ω and 0.65 Ω. The resistance has not quite doubled exactly but it is slightly more than double, this could have been to me measuring the wire a little out.
When the atoms in the wire get hot they start to vibrate. This makes it harder for the current (the flow of electrons) to pass through the wire. The atoms vibrating causes heat which in turn causes the atoms to vibrate at a faster rate. In my experiment I kept the current low to minimise the heating effect as much as possible. I think I was successful in my attempt. The results show that heat did not have a major effect on my experiment. From my results I have found that my first sets of results are the most accurate because this was the set with the lowest current.
Evaluation
The results I obtained from my experiment were quite accurate. The only two that were very slightly out were at the lengths of 50 cm and 80 cm. I think this was due to inaccurate measurement of the length of wire. One millimetre either way of the stated interval could make a difference. My results are still accurate and reliable enough to be used to form a conclusion and to show that my experiment was a success. I used sensible length intervals and I gathered enough results to form a conclusion and to find a pattern. I found that as the length of the wire increased so did the resistance.
During the experiment I encountered no problems with any of the equipment and I had no problems in getting the equipment I required. Everything went according to plan, I had plenty of time and I used it wisely. If I could do the experiment again I would measure the length of the wire and ask somebody for a second opinion. In doing this I might have removed the slight anomalies. Also I would have done the experiment with the same variable but change the temperature of the wire.
To extend the enquiry further I would investigate other things that affect resistance such as thickness of the wire, material of the wire and temperature of the wire. If I did this I could collect all the results together and see which variable had the greatest effect on the resistance.
