What Factors affects the resistance of a wire?

• The material of the wire must also be kept the same throughout the experiment as different materials have different conductivity.

• Maintain the same apparatus, for more reliable, accurate results.

• I should also take more than one result so that I can work out an average, this will help me to detect anomalous results, which can then be repeated to ensure that the most accurate average possible is gained.

• Make sure the voltage on the power pack is the same throughout the experiment for more accurate and reliable results.

• Make sure that the surrounding room temperature remains the same or the particles in the wire will vibrate faster (if the temperature is increased), this will therefore have an effect on the resistance. It may cause it to increase it slightly.

• Contamination: Make sure that the equipment used is not contaminated. This may have an effect on the experiment e.g. crocodile clips which are rusty. This would result in unreliable and inaccurate results.

Prediction:

“Resistance is a force which opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit”. Resistance is measured in ohms (     ). To work out the resistance you would use Ohms Law:

                  Voltage (V) = Current (A) x Resistance (   )

                                 The equation to work out RESISTANCE is:  

Preliminary Work was completed. But why do preliminary work?

• To look for any errors and make corrections. By making improvements I shall ensure more accurate and reliable results.
• It allows me to practice the techniques, so I get more accurate, reliable results.
• It will allow me to assess equipment and to see if they allow me to get good reliable results. If not I can change the equipment to ensure more accurate and reliable results.

        

The following equipment were used in the preliminary experiment:

                                                 (Preliminary Work)

Step.1: All the equipment that was needed was laid out in front of me. The

apparatus was set up as seen in the diagram below.

Step. 2: Wire had to be selected out of the following:

             (Thin Wire)………………..36   SWG

                                               34   SWG

                                               32   SWG

                                               30   SWG

                                               28   SWG

                                               26   SWG

            (Thick wire)…………………22   SWG

Step.3: The chosen wire, over a metre long was sellotaped to a metre rule. The first crocodile clip is clipped to the wire at the 0cm position on the metre rule.  The second crocodile clip is clipped to the appropriate position depending on the required length of wire. The power pack is turned on to 3 V. The second crocodile clip would be moved up and down the wire, stopping at: 20, 40, 60, and 80cm.

Step.4: For each interval, the reading was obtained off the ammeter and Voltmeter. You would then work out the resistance using the equation: V= I/R

       I obtained results using wires 36, 34, 32, 30 and 22 SWG.

                                                   (Preliminary work)

Here are tables of results obtained from the preliminary experiment, for each wire.

Wire.36. SWG- (VOLTAGE USED- 3 VOLTS)

Wire.34. SWG- (VOLTAGE USED- 3 VOLTS)

Wire.32. SWG- (VOLTAGE USED- 3 VOLTS)

Wire.30. SWG- (VOLTAGE USED- 3 VOLTS)

Wire.22. SWG- (VOLTAGE USED- 3 VOLTS)

What were the results?

I was pleased with the results obtained from the preliminary experiment. The results in this experiment showed that:

• As the length of the constantan wire increased, the resistance increased.
• As the length of the constantan wire increased, the voltage increased.
• As the length of the constantan wire increased the current decreased.

Changes to the preliminary experiment to ensure more reliable accurate results are shown on the next page.

Changes to Preliminary Work:

• In the preliminary experiment, a range of different constantan wires were tested and used. However in the main experiment only one main constantan wire was used.

• In the preliminary experiment, I only completed each length of the constantan wire once. This would prevent anomalous results form being spotted, which means that the results may have been inaccurate and unreliable. Therefore in the main experiment I shall repeat each length of the constantan wire three times. This will ensure more accurate and reliable results being obtained.

• Be more accurate in my positioning of the crocodile clips for more accurate and reliable results.

• Allow the wire to cool down for a few minutes after each result was gained. This will ensure that an increase in temperature does not affect the results. Doing this will make them as accurate as possible.

What were the equipment used in the actual experiment?

Apparatus:

• Ammeter
• Voltmeter
• A metre rular
• Crocodile clips
• Constantan Wire (longer than 1metre) 28 SWG
• Leads
• Power Pack
• Wires
• Sellotape

Method (actual experiment):

Step.1: All the equipment that was needed was laid out in front of me. The

apparatus was set up as seen in the diagram below

Step.2: Wire had to be selected out of the following:

             (Thin Wire)………………..36   SWG

                                               34   SWG

                                               32   SWG

                                               30   SWG

                                               28   SWG

                                               26   SWG

            (Thick wire)…………………22   SWG

Step.3: The chosen wire, which was 28 SWG, was sellotaped to a metre rule. The first crocodile clip is clipped to the wire at the 0cm position on the metre rule. Power pack was switch on to 3V. The second crocodile clip was moved up and down the wire, stopping (clipped) at the lengths: 10, 20, 30, 40, 50, 60 and 70cm.

Step.4: For each interval, the reading was obtained off the ammeter and Voltmeter. The experiment was repeated twice, to obtain three sets of data. This is because the more data I have, the more reliable results. You would then work out the resistance using the equation:

                       

                          Resistance (    ) = Voltage (V)         Current (A)

                                     

                       R              =       V                         I

                           Results are shown on the next page

Results showing how the length of wire affects the Resistance

Here is a table of results obtained from the actual experiment using the wire 28 SWG.

Averages had to also be worked out- shown on the next page:

Results (continued):

The averages were then worked out so a graph could be drawn. To work out the averages you must add the 3 results of the resistance (    ) for each length and then divide by 3.

           

                     

      1.5 was an anomalous result so was therefore not used.

     

 1.1 and 1.0 were anomalous results so were not used.

After the averages had been worked out, they were plotted on a graph which is shown on the next page.

Conclusion:

The graph on the previous page shows the relationship between the length of wire and the resistance. More specifically, this shows that the resistance of the wire is directly proportional to the length of the wire. The graph shows as the length of wire increases, the resistance increases. This was because in a longer piece of wire the electrons have to travel further, and the chances of collisions with the atoms of the conductor, which result in resistance, are increased which increased the resistance. The graph clearly shows a pattern between the increasing resistance and the increasing length of the wire, as also shown in my table of results. The resistance against the length of wire is a straight line passing through the origin. (as shown on the graph).

It is clear that doubling the length of the constantan wire, doubled the resistance. This is because, doubling the length of the wire, doubled the number of atoms in the wire, and so doubled the number of moving electrons, and so double the number of collisions which doubled the resistance as the speed at which the current flows is halved. This is exactly as I stated in the prediction. Data from the results table backed up these statements i.e. when the length equaled 0.2 m the average resistance equaled 0.9    and when the length equaled 0.4 m the average resistance equaled 1.8     (i.e. it has been doubled.)

Evaluation:

I can simply prove the results obtained from the experiment back my prediction. I was fairly happy with the experiment as I managed to collect three sets of results for each of the different length intervals that were accurate and reliable. I also made corrections to the preliminary wok, which increased the reliability of my results.

When looking at the graph, there are no anomalies. I repeated anomalous results, which again led to a more accurate average. Reasons for anomalous results might have been that I was inaccurate in measuring the length, i.e. the wire was shorter than what it should have been therefore there was less resistance. Another reason may have been that I adjusted the voltage on the power pack by accident. The temperature of the wire may have been lower than the other results due to it being allowed more time to cool down. All of the averages plotted on the graph were close to the line of best fit which results in firm conclusions being reached.

The accuracy of the results were achieved due to being accurate when measuring the length of the wire. You can see that the results were accurate as most results for each length of wire are similar. Another reason for obtaining accurate results was because all the control variables were left constant.

Improvements to the experiment:

• Repeat each length more times i.e. 10 times. This would lead to more results, which would give me a more accurate average.

• Increase the length by every 0.5 m, it would then give more points on which to draw a line of best fit this would therefore make the line of best fit more accurate.

• Wait 10 minutes for the wire to cool instead of just a couple of minutes, therefore the temperature of the wire should be the same each time and therefore not affect the resistance of the wire. This would increase the reliability of the results.

                    Reliability of the experiment is on the next page.

Reliability:  

The overall experiment was very reliable as there were no anomalous results on the graph and all points lie very close to the line of best fit showing that they are accurate and reliable.  

• The predicted results line of best fit is close to the actual line of best fit. This also means that they are accurate and reliable.
• It is also reliable as anomalous results were also repeated and not included in the calculation of the average resistance value.
• Each result for each length of wire was also similar. Therefore the evidence definitely supports a firm conclusion.

Planning section:

You must carry out a calculation to work out predicted resistance values:

     

                                     R = resistance (       )

                                        = resistivity (       )

                                     L = length of wire (       )

                                    A = cross sectional area ( m   )

• 28 SWG constantan wire has a diameter of 0.357 mm. This had to be converted into meters: 0.376 = 0.000376 m

Resistivity of constantan wire is 4.9 x 10     m. 4.9 x 10    m = 0.000000049

• To find the CSA of the wire, you must use the following formula:

                 Diameter        2     =       Radius

           0.000188 m           2     =    0.000188m

Area =      

A      =               x 0.000188

A      =               x 0.000000035

A      = 0.000000111 m

So the cross- sectional area of the constantan wire with a diameter of 0.376mm is 0.000000111m    .

The predicted results for each length of wire is shown on the next page.

1.)