Factors that may affect the experiment.
The independent variables:
- Length
- Cross sectional area.
There are factors that I can change and factors that I can keep the same, but the factor that is uncontrollable is temperature. The temperature in the surrounding area may change, but I can try and keep the wire the same heat by using the same voltage.
If the temperature begins to rise and becomes warmer than when the experiment started, the wire will gain kinetic energy and will therefore not be a fair test.
- As the length increases, the resistance increases.
- As cross-sectional area increases, the resistance decreases.
- As temperature increases, the resistance of the wire increases.
Apparatus
The apparatus that will be used for the preliminary experiment will be:
- Battery.
- Variable resistor.
- Amp metre.
- Volt metre.
- Wires to connect the circuit together.
- Constantan wire.
Measurements
During this experiment I am going to measure the amps and the volts of selected wires and their cross sectional area. I will then work out the resistance of the certain constantan wire.
The measurements that I will be using are;
- Diameter- 0.08
- Diameter- 0.71
Using both of these pieces of wire, separately, I will attach them to the circuit as shown on the previous page. I will then measure the wire to 50cm and take eight readings from it using a variable resistor and then again I will do the same but with 1 metre of the wire. I will do this with both of the diameters.
I will then construct my results on a graph. As this is the preliminary I will not do repeats on the anomalies but for the final experiment I will redo anomalies.
Method of preliminary experiment
- I will first connect the circuit together.
- Then I will connect the wire with the diameter of 0.08 and a length of 50cm.
- I will turn the power supply on using a voltage of 2.
- I will take eight readings from the volt metre and eight reading from the amp metre, using a variable resistor and then I will do the same with 1 metre.
- I will repeat this using the wire with a diameter of 0.71. Again I will do 50cm and then 1 metre.
Analysis of my preliminary experiment
During my preliminary we could not obtain results of the wire with a diameter of 0.08 as it was to thin and the temperature began to rise, therefore it would not be a fair test if I had used that diameter of wire as more kinetic energy would be produced a it would not be Ohm’s Law, because for Ohm’s Law to occur the temperature must remain constant. I decided to try the 0.45 diameter, constantan wire. This was successful and I was able to obtain results from this.
I have decided to use constantan wire with the diameters of 0.45 and 0.71, also I have decided to do four different lengths instead of only two, this way I may gain more accurate results, and there hopefully will be fewer anomalies.
The four lengths that I have decided to use are:
- 25cm.
- 50cm.
- 75cm.
- 1 metre.
Analysis
Through my final experiment I have proved my hypothesis. The experiment supported my hypothesis. As the length doubles so does the resistance, also as the diameter is doubled, the resistance is decreased by half.
This is due to Ohm’s Law, which states the ratio of the voltage across a conductor to the current flowing through it I a constant, the resistance.
The temperature also remained the same throughout the experiment because the results were accurate and therefore it was a fair test because all of the experiments had the same amount of kinetic energy.
In the experiment with the diameter of 0.71, at 0.40 amps with 25cm of wire was 0.14 volts and at 0.40 amps with the length of 50cm, the volts were 0.30, this is nearly double, so my hypothesis is proved, as the length is doubled so will the resistance be doubled.
With the results that I had placed in tables, I constructed two graphs, one for each diameter. On each graph there was one anomaly, so I redid the anomalies so that I could get more accurate results and I constructed another graph to place the new results from the anomalies.
