Physics Gcse Coursework: Resistance of Wire

Physics GCSE coursework: Resistance of wire Aim: To investigate if the length of wire affects its resistance.

Prediction (Hypothesis): I predict that the longer the wire the higher the resistance, and the shorter the wire the lower the resistance. Knowledge: Resistance is that property of electric components that turn electric energy into heat in opposing the passing of an electric current. It can be beneficial, as in electric heaters, or a pest, as in light bulbs, where the heat is produced alongside the light – we want maximum light and minimum heat.Reistance is often unwanted and we try to minimise it since it results in lost energy, which costs money.

Lately superconducters have bee in the news a lot. The are very special conductors which have zero resistance when cooled to a very low temperature. Current may flow for months or years with no measurable loss even when the applied voltage which started the current flowing is removed. There are two equations which determine the amount of current and the power converted into heat in a resistor: V=IR and P=VI respectively, where V is the voltage in Volts I is the current in Amps P is the power in WattsR is the resistance in Ohms The reciprocal of the resistance, 1/R, is called the conductance and is expressed in units of reciprocal ohm, called mho. Some of the properties of resistance may be summarized in a series of bullet points. • If you use resistances in series circuits you get a higher resistance.

• If you use resistance in a parallel circuit you get a lower resistance. • If you use different materials you receive a different resistance. This may because of the internal structure of the material, the way the atoms Aare arranged, or the type of atoms of which the material is made. When metals are heated their resistance goes up. • When semi-conductors are heated their resistance goes down. Fair Test: These are the factors we are going to control: keeping these the same for each test will ensure our results are as fair and accurate as possible.

1. Ensure the temperature is always the same, by doing the experiment in a thermostatically controlled room 2. Ensure you always use the same equipment for this may tamper with results. 3. Ensue you use the same type of wire (for reasons explained in Knowledge) 4. To redo tests several times and create an average to stop outliers.

. Keep the Voltage the same for each measurement. 6. Keep the thickness the same. Equipment List: • Metre Ruler • Power Supply • Ammeter • 1 metre length of wire • Wires for power supply and ammeter.

• Contacts Safety: Ensure no live high voltage wires are exposed; this is done by having a small voltage of 2V. Wear safety goggles to protect eyes from the power supply. Work in pairs to prevent any dangerous incidents occurring. Make sure that all taps are turned off to prevent possible electrocution. Be quiet, talk sensibly, do not shout and always listen to your teacher. Method and Diagram:Step 1: I put on my safety goggles.

Step 2: I set up my apparatus. Step 3: I switched on power supply to 2V. Step 4: Fixed wires to power supply and metre ruler with the wire. Step 5: Attach second wire to the ammeter. Step 6: Leave a ‘loose’ wire from the ammeter so that you can record your results.

Step 7: Move the ‘loose wire along the metre stick with the wire at different lengths (20cm, 40cm, 60cm, 80cm, and 1m) and record results from the ammeter. Step 8: Repeat Step 7 three times and create an average. Step 9: Divide the voltage (2V) by the average results (in Step 8) to find the resistance.Obtaining Results: | | | | | |Length |Current (Amp) |Average |Resistance | |(cm) | |(Amps) |? (ohm) | | | | | | | | | |Expt. |Expt.

2 |Expt. 3 | | | | | | | | | | |20 cm |0. 90 |0. 88 |0. 92 |0. 90 |2.

2 ? (ohm) | | | | | | | | |40 cm |0. 46 |0. 45 |0. 6 |0. 46 |4. 3 ? (ohm) | | | | | | | | |60 cm |0.

34 |0. 34 |0. 35 |0. 34 |5. 9 ? (ohm) | | | | | | | | |80 cm |0. 25 |0.

24 |0. 26 |0. 25 |8. 0 ? ohm) | | | | | | | | |100 cm |0.

20 |0. 20 |0. 21 |0. 20 |10.

0 ? (ohm) | Conclusion Resistance is directly proportional to length, within the bounds of experimental uncertainty. This is consistent with the equation R=pL/A, an equation well know to physics students. This says that the resistance of a wire is proportional to resistance and is the equation of a straight line graph of resistance against length. Analysis:Resistance increases with the length of wire, from the graph within the bounds of experimental error resistance is proportional to the length of wire. We know that series resistances increase the total resistance, so the same resistances in series multiply the resistance by the number of resistances.

We imagine a wire being a series of identical resistances connected in series, so it seems logical that resistance is proportional to length; we might ask the question behind our results – what is resistance? What is it about the structure of the inside of a wire that makes the resistance proportional to the length of the wire?We know that electric current is carried by electrons, which are light and negatively charged. The insides of the wire are made up of atoms, and the electrons have to get past the atoms. Is it only that the number of atoms that increase in proportion with the length of the wire that increases the resistance. Better still, is it the number of atoms that each electron must make its way past? That would give a concept like electrical resistance which maybe we could use to explain other things.

For example, in metals, the resistance increases with temperature.If we imagine the wires’ atoms jumping around and obstructing the passage of the electrons, if we heat the wire, the atoms would jump around more and be more obstructive. This does not explain what happens in semiconductors, for which the resistance decreases with increasing temperature. Metals have a similar structure of positively charged atoms surrounded by negatively charged electrons, but the structures for semiconductors and carbon might be different and more complicated.

On top of this, how much do we know about the wire? Is the length the only thing about the wire that can affect its resistance?Can we think about a thicker wire and resistances in parallel in the same way as we thought about resistance and length earlier in this conclusion? Can we take the length or breadth separately or both together and take only cross sectional area into account? Does the cross sectional areas vary along the wire and how will this affect our results? To be sure, of our conclusion we need to test a wider variety of materials, including semiconductors and graphite carbon, and to find reasonable hypotheses for any results in those experiments that may differ from those here.We should also, find explanations for the temperature dependence of resistance of semiconductors. Evaluation: The results of our experiment confirms our hypothesis that the longer the wire the higher the resistance and vice versa. It remains to consider how we could improve our experiment to reduce error, and make our result more reliable and accurate. We should have taken several lengths of much longer wire of differing materials and evaluated each one in the same way.

The wires should be as long as possible to reduce the proportionate errors in easuring lengths, and to reduce the proportion of the resistance that is lost by the contacts contact with the wires –these contacts could also have resistance, and we need to minimise this proportionately. We should also make sure that the cross-sectional area is as close to, as possible, the whole length of the wires. We should also do a full error analysis, so we can estimate the inaccuracies, this would enable us to put error bars on our graphs, and this would be an easily recognisable way of showing the accuracy of our results.