Ammeter and a digital Voltmeter

Current - since it is the potential difference across the wire that is being measured, we have to make sure the current is kept the same for every reading. Again this is because if the current is not controlled, an increase would cause the wire to heat up and this would have an affect on the resistance. So I have chosen 0. 2 Amps as the standard current reading across the circuit. Accuracy All round accuracy is very important when carrying out an experiment, so that the results obtained are reliable and then truthfully display the trend that should be seen.

Firstly, to accurately measure the wire, it will be firmly placed onto a metre stick so there are no coils in the wire and it can be measured along the metre stick with considerable precision. Since the crocodile clip heads are 3mm thick, 2cm of extra wire will be measured so that 0. 5 cm can be folded over at each end and the clip can get a firm grasp of the wire.

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Amongst the apparatus, some of the items were included to enhance the accuracy and provide precise readings. We used a digital Ammeter and a digital Voltmeter. Both these devices measured to the nearest hundredth.

I intend to carry out the experiment twice, so that I have two sets of results. If I then notice an anomaly between any two findings I will repeat that one a third time. All this is essential in order to attain reliability with the results because firstly, any anomaly can be immediately recognised and stamped out.

Then an average is taken to calculate the final resistance, which maximises accuracy and diminishes any discrepancy with the findings. Apparatus When setting up the apparatus for this experiment we require:  1 Power Pack.

The above table of results displays the various lengths of wire used, and the two sets of readings for potential difference at those lengths.

The table shows that we carried out repeated readings, as this is appropriate when considering a particular factor, where accuracy is important. The average has been taken of those readings, and finally the resistance was calculated. Firstly, the current was recorded as 0. 20A and not 0. 2A because then the reading could only be out by 0. 01 of an Amp. This meant that that there was a lower percentage error, if the calculation had been made wrong, which enhanced accuracy. The lengths were measured to 0. 5cm and nothing more defined because the crocodile clip heads that determined the length being employed, had 3mm ends.

So it would have been difficult to work out where that particular length ends, under the grasp of the clip. However, although they were calculated to 0. 5cm, as the lengths got shorter the precision increased when taking the measurements. This became important because as the lengths got smaller, creating an error with the measurements created a greater percentage error, as the overall length that was being measured inaccurately was small. For example, there is a 2. 5% error chance when measuring to 20cm compared to a 1% error when trying to use 50cm.

This shows that as the length decreases, the measurements should be taken with more accuracy and precision, to minimise the result of having a large percentage error and creating an anomaly with the final result. The potential difference was measured to 2 decimal places, as this is a simple but defined way of recording such figures. By only having numbers up to 2 decimal places the number remains meaningful and does not look unprofessional, as it is to a hundredth of the value. However, when we took the average between the two sets of reading for potential difference, we recorded these to 3 decimal places.

Since a number of the two readings at a particular length had a difference of only 0. 01V between them, if the resulting average was rounded off to make it to 2 decimal places, this value would be the same as one of the two readings. So we had to keep it to 3 decimal places so the average read exactly half way between the two readings. Finally, the resistance was kept to 2 decimal places, as it is a short but accurate way of communicating data. Also, this is the most precise value that can be plotted correctly on a graph.

So to ensure the graph point were easy to plot, it is advisable to have these results processed to 2 decimal places. Although approximately ten was an optimum number of readings to be taken, I took the lengths of wire at every 5cm. This was so that the graph would immediately highlight an anomaly or a point that seemed distant from the bulk of the points, and therefore the line of best fit. However, from the results we can see that the two sets of readings for each length agreed with each other and did not exhibit any conflict between the readings.

So we did not have to repeat any of the findings a third time, which would have been implemented if a further reading was required to settle a dispute between any of the initial two readings. Overall, we can see that the experiment was relatively successful as we used precision and maximised the accuracy within the experiment, in order to obtain reliable and true results. Analysis From the results it can be evidently seen that the resistance increases as the length of the wire increases. This supports my initial prediction that an increase in the length of the wire would subsequently cause an increase in the resistance.

This was true because when there is more wire there are therefore more atoms. So when electrons are flowing as current, they have to pass more atoms when the length of wire is greater. So as the current is travelling there are more collisions between the flowing electrons and atoms in the wire. This means the resistance against the current is higher. However, when the length is shorter there are fewer atoms to obstruct the current, so obviously there are less collisions. This means the resistance is lower.

This trend remained accurate throughout the experiment as the resistance continued to increase alongside the length of wire. By looking at some of the readings that were obtained we can confirm that the prediction turned out to be accurate and the results did in fact support the prediction. When the length of the wire was 90cm the resistance was 8. 35 and 30cm shorter, at 60cm the resistance was 5. 60. Finally at a length of 30cm the resistance was 2. 85. From just these three findings we can see a general trend that as the length got shorter the resistance decreased.

Also, from these three readings I can see that as the length went down by 30cm each time, the resistance decreased by approximately 3. This shows that the results support the theory that resistance is proportional to length. By looking at all the readings it can be seen that as the length of wire went down from 100cm to 10cm, the resistance decreased from 9 to 1. This supports the idea that resistance is proportional to length, because overall the resistance decreased systematically and in relatively equal steps, similar to the lengths.

Graphically, we can reconfirm this theory, as the line of best fit is a line and not a curve, so as the length increased the resistance also increased proportionally. Overall I can confirm that my prediction was in line with the results I obtained since it turned out that the resistance did increase as the length of wire increased. This also supports the theory which explains that when there is more wire there are more vibrating atoms obstructing the flowing electrons, so resistance against the current is therefore higher. Evaluation Procedures and Results.

I can confidently say that the experiment was relatively successful and produced results that can be considered as reliable and correct. After completing the experiment the first time, we carried it out again to ensure that there was no major difference between the two readings. We had previously decided that if there had been any major anomaly we would repeat those specific readings a third time to retrieve a true and suitable reading. However, this was not required, as both readings for each length did not conflict with each other.