Measurements and ranges
To record the resistance from the change in the length of the wire I will be measure every 10cm of the wire up to 60cm, as this will give me a good set of results. I will also do each measurement three times and take the average result. This will give me accurate results.
To record the resistance from the change in the thickness of the wire I will measure each wire twice with a 10cm wire. I will alter the variable resistor by 2.5cm after each result and will do this five times (which means I will have moved the variable resistor by 10cm after five results have been taken). On each average result I will use Ohm’s Law to calculate the resistance.
Method
First, the power pack was set up with wires leading out of it from the AC outlet. The power pack will be set at 4V. This first wire is connected to the variable resistor; a wire is then connected from the variable resistor to the ammeter. Another wire is connected from the ammeter to the voltmeter. A crocodile clip should be connecting the voltmeter to the wire that is being tested. Another crocodile clip connects the wire back to the power pack. The results are taken, starting at the first wire (0.71mm) with the crocodile clips 10cm apart. After the results have been taken the length between the crocodile clips is increased to 20cm. This process continues up to 60cm. Each length is repeated three times and an average is taken to give a good accurate set of results.
When the thickness of the wire is being tested the equipment is set up in the same way but instead of increasing the length of the wire, the clips are just moved onto the next thickness of wire. Also for this experiment the variable resistor is altered by a small amount after each result has been taken. As in the first one three results are taken and the average is found.
After any set of results has been taken the power pack is switched off as the wire can heat up causing the resistance to be altered.
Obtaining Evidence
Tables of results
Length: Test 1
The resistance is found using Ohm’ s Law
Length: Test 2
Length: Test 3
Length: Average results
Average results
Tables of Results 2
Thickness: 0.71mm wire
Thickness: 0.56mm wire
Thickness: 0.45mm wire
Thickness: 0.31mm
Thickness: 0.28mm
Average Resistance
Conclusion
My graphs show that my prediction was correct. As the length of the wire increased the resistance also increased. This is because as the wire increases its length the electrons in the current have to travel through more fixed particles, causing more collisions and therefore raising the resistance.
My prediction for the thickness was also correct. As the wire gets thinner the resistance increases because there is less room for the electrons to pass through the fixed particles which also causes more collisions and a higher resistance.
My graphs also show three anomalous results in the graph testing the thickness of a wire. This may have been due to the crocodile clips touching another wire and causing the resistance to change.
Evaluating Evidence
Accuracy
To make my measurements accurate I made sure that the length of the wire was measured to the nearest millimeter. I also took three results from each test and took the average from the three results to give a very accurate set of results. I then took the resistance from each set of results and then took the average resistance from every result taken. I believe that my results are very accurate as the averages that I took made the experiment precise.
Objective
The aim this experiment was to test the resistance in a circuit when the length and thickness are the variables. I believe that I have achieved this because I have found a relationship between the resistance and the variable. This relationship is shown in the graphs.
Reliability
I believe that my results are accurate because I tested each result three times and took the average of the three. This was repeated over all of the experiments and the average resistance was also tested to give and accurate measurement.
Improvements
To improve my experiment I could make sure that the crocodile clips don’t touch any of the other wires therefore affecting the resistance reading.
Extension
To further add evidence to my experiment I could test the other two factors that affect the resistance. These are the temperature and material of a wire. This experiment would prove that each factor in the change of resistance in a circuit has a relationship with the average resistance. When the material of a wire is the variable the resistance will change because if the wire has a high density there will be more fixed particles in the wire causing high resistance, but when the wire has a low density the fixed particles will be less so there will be a lower resistance.
The temperature will make a difference because if the wire is hot there will be a lot of kinetic energy in the variable and the particles will be moving about much faster than usual and this will make the resistance higher as it is harder for the current to flow through the wire when the particles are moving around so quickly.
