Therefore, to calculate resistance, the potential difference and current need to be known. Potential difference is measured in Volts with a Voltmeter. Current is measured in Amperes (or Amps as they are more commonly known) with an Ammeter. Resistance is measured in Ohms (? ). – Electron – Atom At atomic level, resistance is the action of atoms vibrating in the wire, blocking the flow of electrons. In effect, resistance is a “bottleneck”. The diagram below illustrates this: On their journey, the electrons do not have a clear path because of the atoms in the way. This slows them down.
I predict that as the length of the wire increases, so does the resistance. This is because, as the length of wire increases, the number of atoms in the wire will increase too. This means that the electrons’ route will be obstructed even more. Another way of saying this is that the length of the wire is proportional to the resistance. Proportionality can be seen in a results table when both sets of results increase. A proportional graph looks like follows (note the line of best fit should go straight through the origin): Below is a diagram of the circuit I will set up: – Ammeter – Adjustable Length Wire.
– Voltmeter – Variable Resistor This circuit will show how the resistance changes with the length of the wire. The Voltmeter is in parallel with the adjustable length of wire, so will measure the voltage of this component. To stop the adjustable length wire from heating up and thus affecting the results, a variable resistor is put into the circuit. This can be adjusted to keep the current constant throughout the experiments and thus keep the temperature constant. The Ammeter is needed so the resistance can be calculated. The “Adjustable Length Wire” is set up as follows.
The Constantan wire is attached to the ruler so its length can be measured easily. Two crocodile clips will connect this set-up to the rest of the circuit. I will take 10 measurements and 3 repeats of each to make sure that the results are accurate (if a mistake has been made in one set of results it would be clear by looking at the other 2 sets). The first measurement will be taken 10cm along the wire, and the next 9 will be taken at 10cm intervals. The average resistance will be calculated by finding the mean resistance of the 2 closest sets of results. This experiment must be a “fair test”.
This means that certain factors must be kept constant throughout every test done. In this experiment, the “constants” are: Type of wire Temperature of wire Current in the circuit Length of wire (other than adjustable length wire) Battery size Voltmeter used Ammeter used Circuit set-up To ensure that the final experiment is thoroughly planned out and thought through, I will conduct 2 preliminary experiments. These experiments will mainly aid in deciding which current constant to use. The results from the 2 experiments are shown below: Length of wire (cm) Current (A) Voltage (V).
6A, the Voltage readings for 80cm and over were too high to be shown on the Voltmeter. The graphs for the 0. 2A and 0. 6A results are located on the next page. Obtaining and Presenting Evidence I chose to keep the current a constant of 0. 4A for the proper experiment. The 3 sets of results from the final experiment are shown below. Test number Length of wire (cm) Current (A) Voltage (V) Resistance (? ) To be able to plot these results, the average from the 3 resistance calculations from each length had to be found. The table below contains these average resistances. Length of wire (cm).
Average Resistance (? ) to 2 decimal places 1 Considering Evidence The results from the 0. 4A current graph (found on the next page) show simply that as the length of the wire increases, so does the resistance in the wire – the two values are proportional. This is because as the length of the wire increases, the number of atoms that could block the path of the electrons increases. This in effect increases the resistance. As mentioned earlier, proportionality on graphs is shown when both values increase.
This is certainly true on the 0. 4A current graph. However, the line of best fit does not pass directly through the origin. Despite this, I still conclude that my prediction was correct. This is because I believe that there was already a certain amount of resistance (around 0. 5? ) in the circuit before any extra resistance was added. Evaluating I believe that my experiment was carried out well, but as the results show, there is room for modifications and improvements if I were ever to carry it out again. I believe the results are reliable enough to support my conclusion.
There is a slight anomaly at 90cm on the 0. 4A current graph. This is also seen on the 0. 2A current graph at 80cm. This might have been because between 80cm and 90cm, the wire may have been bent. This would mean that a result taken at what was supposedly 80cm could be closer to 82cm. If I were doing this experiment again, I would make sure the wire was absolutely straight. A precaution could be to stick Sellotape just before every measurement. On the subject of the wire, the crocodile clips were not very accurate when being placed every 10 centimetres.
A more accurate appliance to use could have been, for example, a knife or needle. This is because these objects have a smaller surface area and so could be more accurately placed where they needed to be placed. Another major problem in the experiment was that there was approximately 0. 5? in the circuit before any extra resistance was added. This resistance may have been from components already in the circuit, or the connections between them. To reduce resistance in connections, higher quality ones could be used. Ideally, gold connections would be the best, but a cheaper alternative would be brass.