# Physics AT1-Resistance of a wire

The electric current in a solid is a movement of tiny negative charged electrons. As these electrons move they collide with the particles of the solid which makes the electrons movement difficult.

Resistance is a measure of how difficult it is for the electrons to move. A high resistance means that the electrons will make lots of collisions and lose lots of energy. The circuit itself can resist the flow of particles if the wires are either very thin or very long. e.g.The filament across an electric bulb is quite thin as needs to resist the flow of particles for the bulb to glow. Resistance is measured in ohms. The higher the resistance, the lower the current.

If there is high resistance, to get the same current a higher voltage will be needed to provide an extra push for the electricity. Some metals have less resistance than others. Wires are always made out of copper because copper has a low resistance and therefore it is a good conductor. The length and width of a wire also has an effect.

Ohm’s Law: The current is proportional to the voltage, provided the temperature remains constant.FactorsThe resistance of a wire depends on certain factors. Some of these variables are listed below:ï¿½ Length of wireï¿½ Diameter or thickness of wireï¿½ Temperature at which wire is keptï¿½ The material of which the wire is made out ofï¿½ The potential difference or voltageï¿½ Humidityï¿½ Cross sectional areaï¿½ Voltage across circuitI will be investigating the diameter of a wire and how it effects the resistance. All the other factors will have to be kept constant whilst doing the experiment to ensure that the investigation is a fair test. I have decided to investigate how the diameter of a wire affects its resistance because other factors such as temperature are harder to control and get a good set of results. The way in which the diameter of a wire affects the resistance is an efficient experiment to do because:* A graph can be plotted easily* There is a large range of results* The results can be recorded easilyIn order for the investigation to be a fair test, all other factors should be kept constant.

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The investigation has to be done in a fair way otherwise the results will be inaccurate and the conclusion will be incorrect. The variables that must be kept constant are:1) Temperature When the temperature of a wire increases the resistance of that wire increases. This is because when the temperature increases the atoms inside the wire vibrate more vigorously because of the increase in energy. This means that the electrons have more difficulty getting through the wire as they collide with the other in their pathway. This increases the amount of collisions therefore there is more resistance. To make sure the temperature does not effect my result too much it is essential I use a low voltage because it means a low current, which won’t heat up the wires. If a high voltage is used the energy would be in form of heat which would make the experiment unfair. The investigation will be done at room temperature.

The temperature cannot be investigated because it is hard to control the range of temperature needed without the correct apparatus.2) Length of wire The longer a wire, the larger the resistance. This is because there are more atoms in the wire so there is more chance that the electrons would collide with one of the atoms therefore there is more resistance. In a long wire electrons have a longer distance to travel so there are more collisions so this will change the resistance up and in a short wire electrons have a short distance to travel so they collide less and therefore there is a lower resistance. This is because when you have a long wire, the electrons have to squeeze together for longer to be able to pass through the wire than they do in order to be able to pass through a short wire. It is important to keep the length of the wire the same each time otherwise it could not be certain which variable is changing the resistance. If I had a 30 cm wire and a 60 cm wire, the 60 cm wire would have a resistance twice that of the 30 cm wire.

3) Type of material Different materials have different resistances because the materials’ atomic structures are different so some wires have low resistances and some have high resistances. Therefore it is important to keep the material the same throughout the experiment. If different materials are used throughout the investigation, it will affect the results. For example if sometimes copper is used and sometimes nichrome is used, the results where copper is used will be of a low resistance because of the material and not because of the diameter of the wire. Throughout the experiment nichrome wires will be used. The type of material will affect the amount of free electrons that are able to flow through the wire. If the particles in the material are tightly packed together, the electrons will have more collisions and therefore more resistance.All these factors must be kept constant to make the investigation fair.

All the other factors must also be kept constant as well. The same apparatus must be used throughout the investigation. It is also important to take two repeats and find the mean so if one result is very inaccurate, the other will average it out.QuestionWhat effect does the diameter of a wire have on the resistance through it?PredictionMy hypothesis is that the thinner the wire, the higher the resistance. The thicker the wire, the lower the resistance.

This is because the thinner the wire is, the less paths there are for electrons in the wire therefore the harder it is for current to flow. This results in the energy not being able to spread out as much, so the resistance will be higher. This theory is similar to that of a door, where people represent the electrons and the door represents the diameter of the wire. If the door is wider, more people can get through, more easily. If the door is small, people have more difficulty and not as many people can walk in or out of the door. It is the same principal for electrons. If the diameter of a wire is thicker more electrons can go through the wire, therefore less resistance.

The atoms from the metals cannot stop or collide with as many electrons because the diameter of the wire is larger.This diagram shows the negatively charged electrons travelling through a wire colliding with the wire particles. The more these electrons collide the more resistance there is. In a thick wire there is more space in between the wire particles and the electrons will collide less. In a thin wire there is less space between the particles and so the electrons will collide more. This is why I believe that the thinner the wire, the higher the resistance and the thicker the wire, the lower the resistance.

PlanTo prove the prediction above I plan to do as follows. I am going to test the resistance through different diameters of wires. To do this I will need a voltmeter, ammeter, power pack and some different wire diameters. I plan to test five wires all with different diameters. I plan to set up my circuit as shown below:Where the wire is position I will have a pair of crocodile clips to hold it in place.

I plan to use 70cm of each nichrome wire and I plan to coil each wire. To help keep my results accurate I plan to only use a low current when testing; this will keep the temperature of the wire down. For each wire I plan to take one reading from the voltmeter at a constant current of 0.5 A. I then plan to repeat the reading of each wire three times and take the average result .

I shall then be able to calculate the resistance of the wire using the equation resistance = volts/amps and represent this data in the form of a graph.Fair TestI have already mentioned which factor I am investigating and which factors I will keep constant (see pages 1 and 2). I will do the following things to make the experiment a fair test:* Use the same material for each wire* Use the same length of each wire* Take readings using a low current (keeps temp.

down)* Use same equipment for each testSafety PrecautionsI will take the following precautions and make sure others are safe as well:* I will wear safety glasses* I will make sure there are no bag or obstacles on the floor causing a hazard* I will be careful with the electricity present* I will not run around* I will not touch live wiresMethodApparatus* Voltmeter* Ammeter* 2 Crocodile clips* 5 nichrome wires (0.28mm, 0.31mm, 0.40mm, 0.45mm, 0.50mm)* Power Supply Pack* Circuit wiresI first set up the apparatus as shown below:Then for each diameter of wire I followed the following steps:1. I measured 70cm of the wire and coiled it around a pen2. I placed the coiled wire in the circuit attaching it with the crocodile clips3.

I took a reading of the voltage through the wire at one certain point, which was 0.14. I presented the readings for the wire in a table of voltage against current (V against A) and calculated the resistance which is voltage divided by the current (constant at 0.5 A)5. I repeated the readings (using the same equipment) for the same diameter of wire three times to make sure they were accurate6. From the results I took an average for resistance7. I then repeated the process for the other four wiresResultsFrom the following results I will produce graphs to show what was found out more clearly.Set 1Wire Diameter (mm)Current (A)Voltage (V)Resistance (Ohms)0.

280.55.711.40.310.

54.28.40.

400.53.16.20.450.

52.040.500.51.

42.8Set 2Wire Diameter (mm)Current (A)Voltage (V)Resistance (Ohms)0.280.55.

811.60.310.54.38.60.400.

53.46.80.450.

52.550.500.51.32.6Set 3Wire Diameter (mm)Current (A)Voltage (V)Resistance (Ohms)0.280.55.

611.20.310.54.28.40.

400.53.36.60.

450.52.34.60.500.51.

32.6Average SetWire Diameter (mm)Average Resistance (Ohms)0.2811.40.318.40.

406.50.454.

50.502.6ConclusionThe results shown on my tables and my graph clearly show that the thinner a wire the greater the resistance of that wire .From my tables you can see that I got three sets of results. My repeated results all (to a reasonable degree of accuracy) agree with my first set.

From my graph we can clearly see the average results and also see that there is one anomaly, which does not fit in with my line of best fit. Looking at the table I can see that it is not just one reading that made the average an anomaly. There could be several reasons for the anomalous result. Firstly maybe the wire I used had been damaged from previous experiments or perhaps it was not exactly the diameter 0.31mm. Secondly maybe I didn’t read off the voltmeter accurately. Thirdly, I used crocodile clips to fix the wire and perhaps I didn’t fix the wire sufficiently well in the clip.

I observed that the thinner a wire the higher the resistance. This is because of collisions inside a wire. Imagine a metal wire – it contains lots of particles which make up the wire. The electrons have to travel through this wire.

As the electrons travel through the wire they will collide with the particles of the wire. The more collisions the electrons have, the higher the resistance. However, in a thick wire the particles are more spread out and the electrons have more room to travel through. There are fewer collisions and hence the resistance is less.Even though there is a result which doesn’t fit the pattern, the majority of results still follow my prediction.

Improvements and EvaluationAlthough I took precautions to ensure this was a fair test, there were some areas where accuracy could have been improved. The anomalous result suggests that I would need to repeat at least that part of the experiment for that width of wire. It could be that I didn’t accurately measure out 70 cm of wire or I didn’t read the voltmeter correctly. However, I think this last explanation is unlikely because I read the voltmeter three times and each time the reading was almost the same (4.2,4.

3,4.2). This suggests to me that the reason for this discrepancy is more likely to be an inaccurate measurement of either the width or length. There is also the question of whether the current was measured accurately.

Repeating my results more than 3 times would further improve my results and maybe correct the anomaly. To improve my experiment I should have taken more time making sure wires are correct lengths and thickness.Further work that could be done is to look at each wire in more detail. Trying more currents and investigating more factors for example or maybe trying more diameters of wires would be further ideas.

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