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# Resistance in a wire

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How the Resistance of a wire is affected by its length

This investigation will determine how changing the length of the wire, when passing an electrical current through it, will effect its resistance.

Resistance- “the property of failing to conduct electricity or thermal energy”

Introduction

In the conduction of this experiment I will be examining the resistance of a wire. This experiment queries the relation between voltage and amps flowing through 5 different thicknesses of wires. Electricity is transported through the wire by electrons. When a circuit is switched off and there is no electric current present the atoms are able to move freely, producing good electrical conductors. When there is an electric current they all move in the same direction, the negatively charged electrons all move towards the positive sides of the supply. To enable unrestricted movement through the circuit atoms transfer electrical energy therefore when an electrical current conducts through a metal wire, one or two electrons possess sufficient energy to move away from the pull of the nucleus and become free. These free electrons move in rapid unordered motion, changing direction during the collision with positive ions. When an electron collides with a non-moving atom it is resisted.

Electrical conductors resist a current flowing through; these units of resistance are measured in Ohms. When the electrical current reaches a resistor such as a bulb or a motor it slows down and releases energy supplying the resister with a useful property such as the following electrical sources: thermal, light, sound or kinetic energy however also causes a loss of energy through waste energy. For example the filament of a light bulb generates a lot of resistance in that section of the circuit and so the energy from the flow of electrons is transferred into light and heat is the wasteful product of energy. Resistance slows down the electrical current flow therefore as the resistance increases the current decreases. All substances are made up of atoms, which have a nucleus that is made up of protons and neutrons which are surrounded by electrons. Protons are positively charged particles positioned in the nucleus of an atom. The nucleus is the central part of an atom that contains both positively charged protons and uncharged neutrons. Neutrons are a particle with no electrical charge found in the nucleus of most atoms. Its mass is similar to that of a proton. Electrons are a negatively charged particle orbiting in shells around the atomic nucleus.

Hypothesis

My preliminary hypothesis examines how the diameter of a wire affects resistance.The diameter of the wire will have an affect on the resistance of a wire. This is because the electrons have to compress together more to pass through a thin wire than they do to pass through a thick wire. To execute a fair preliminary experiment I must maintain the same length wire, just altering thickness. I can predict that the thinner the wire the higher the resistance.

My hypothesis questions the relationship between resistance travelling with in a wire and the distance. The shortest measured length of 10cm acquires the least resistance, therefore my prediction suggests as the length increases the more resistance generates and the current will weaken. The longer wire introduces more ions throughout the length or the wire therefore more resistance is present. I believe this because the longer the wire the more stationary ions there will be for the moving negatively charged electrons to collide with.

Before conducting an experiment a risk assessment must be performed to identify the possible dangers incorporated with the investigation. This is a necessity because we need to recognise dangers which may occur when commencing an experiment. This allows the correct understanding of how to appropriately utilise the equipment and allows damage and injury prevention.

 Risk Hazard Solution Hot wires When the electrical current is passing through the wires they will produce a lot of thermal energy and touching them could cause a burn t Make sure all components are turned off before touching the wires, avoid contact when power supply is on. Electricity Electric shocks can occur if the electrical components come into contact with water or the voltage becomes too much. Keep the voltage at an appropriate level and keep all fluids well away from the circuit, as water is a good conductor of electricity. Do not try and adjust the circuit while the components are switched on.

Health and Safety requirements

When conducting an experiment health and safety requirements must be adhered to, to prevent injury. To follow safety precautions correctly the wire must be carefully monitored and contact avoided when thermal energy increases. Also each time the crocodile clip is removed and attached to the wire check the power pack is correctly switched off to allow the thermal energy in the clips to reduce. You must acknowledge the potential hazardous aspects to maintain safe.

Equipment for preliminary experiment

The equipment required is as follows:

• A power pack
• A Volt meter
• An Amp meter
• Constantine wire (5 thicknesses)
• Electrical wire
• A Crocodile clip

Method

I am aiming to deduce which diameter of wire contains the largest range or resistance following the connection of voltage and amps. To extract this information I conducted a preliminary experiment in which I obtained 5 different thicknesses of wires, all attached to a wire bridge with a measurement of 100cm. The power pack supply will produce an electric current which will be delivered to an ammeter which displays a reading of the amps travelling through the circuit.

The wire with the smallest diameter obtained the widest range of resistance as a thin wire has fewer electrons to carry the current than a thick wire therefore the resistance is higher.

Resistance in a wire increases as:

• The length of the wire increases
• The thickness of the wire decreases

Preliminary Experiment

The equipment was set up the same as the diagram above. The apparatus enabled the correct conduction of the preliminary experiment which determined the widest range of resistance with in the wires. The Ammeter measures the current in amps flowing through the component, it is only able to work correctly if connected in series whereas the voltmeter measures the voltage in volts across the component and must be placed in parallel around the component under test. The power pack will have a cable connected to the set of wires. (Connected to the wire that is being tested at that present time). Then a cable connected to the ammeter, another cable will exit the opposing side of the ammeter, completing the circuit. Along a cable there will be two more cables attached to a voltmeter to record results and enable a constant voltage, which allows a fair test. Following you should connect the crocodile clip to the appropriate wire. This is then attached to the correct length of wire required to determine.For example the first wire under investigation 26swg. Avoid a high voltage for example in my experiment I used 6V, observe the readings on the ammeter and voltmeter. When this process is successfully completed switch off the power supply to the circuit and alter the length of wire being tested be removing the crocodile clips and applying them at an extended length. Each wire must be tested like this at 100cm. When this is completed then change the crocodile clip to the length of 10cm carrying out the same procedure each time.

I calculated the resistance by processing the data collected, I divided the voltage by amps (also known as Induction) using Ohms law. It was concluded that 34 Swg the wire possessing the smallest diameter, this was done by retrieving the widest range therefore allowing an accurate resistance when investigating the wire every 10cm’s.

Experiment using the wire with the widest range

To conduct the experiment, you should carry out the previous experiment in the preliminary experiment. However this time you only use the wire that had the largest range from the preliminary experiment, which I determined as 34swg. For this wire you measure the Voltage and Amps exactly as you did before however this time you measure it for every 10cm and record your results, extract the range (resistance). From this you can look to see whether the resistance increases or decreases as the wire increases in length, to make sure your results are correct you could try it again to get an average reading. This enables you to view whether the results are strong evidence to my hypothesis.

When I measured the wires at the lowest distance of 10cm I discovered that there was less difference between the wires than at the furthest distance of 100cm.  At 10cm there was a difference of 0.95 ohms, from the thickest to thinnest wire. However when it was at 100cm the difference was 7.89 ohms. This indicates the resistance increases as the length of wire increases. This is one factor which affect and alters resistance. The current can be found from Ohm's Law, V = IR. The V is the battery voltage, so if R can be determined then the current can be calculated.

The current through a component depends on the potential difference across the component and the resistance of the component. Results

Why do we get resistance?
An electric current flows when charged particles called
electrons move through a conductor. The moving electrons can collide with the atoms of the conductor. This makes it more difficult for the current to flow, and causes resistance. Electrons collide with atoms more often in a long wire than they do in a short wire. A thin wire has fewer electrons to carry the current than a thick wire.

From the results of my preliminary experiment I established that as the wires thickness decreases the resistance increases. This is as there is a higher quantity of space in the thicker wire therefore low resistance, as they have more space to move freely whereas in a thin wire the movement is restricted and the electrons are compact.

Below is a diagram to represent this;   Below are the results I obtained from experimenting the diameter at 10cm’s:

 10cm Voltage (V) Current(A) Resistance(Ohms) 26 swg 2.93 7.95 0.4 28 swg 3.41 6.39 0.5 30 swg 3.95 5.11 0.8 32 swg 4.16 4.56 0.9 34 swg 4.58 3.46 1.3

Below are the results I obtained from experimenting the diameter at 100cm’s:

 100cm Voltage (V) Current(A) Resistance (Ohms) 26 swg 5.28 1.72 3.1 28 swg 5.47 1.22 4.5 30 swg 5.63 0.80 7.0 32 swg 5.71 0.73 7.8 34 swg 5.81 0.53 11.0

The tables represent that as the Voltage increases with the decreasing thickness of the wires therefore the Current (Amps) decreased. Demonstrating that as the resistance increases the thickness did, this is the second factor which affects resistance. The 34swg wire gave the widest range of resistance therefore I will use this for my experiment as this will give me a clear apparent result.

Results for first test

Voltage used 6V

Thickness used 34wsg

 Length (cm) Voltage (v) Current(A) Resistance (Ohms) 10cm 4.58 3.46 1.3 20cm 4.99 2.22 2.3 30cm 5.23 1.58 3.3 40cm 5.4 1.23 4.4 50cm 5.53 1.02 5.4 60cm 5.59 0.86 6.5 70cm 5.61 0.74 7.6 80cm 5.63 0.65 8.7 90cm 5.68 0.60 9.5 100cm 5.81 0.53 10.9

This table presents the evidence that as the length of the wire increases the resistance increases. This is clear as the wire extends 10cm the resistance enlarges. This is because as the length increases resistance occurs more frequently.

Results for second test

Voltage used 6V

Thickness used 34wsg

 Length (cm) Voltage (v) Current (A) Resistance (ohms) 10cm 4.48 3.54 1.3 20cm 4.93 2.17 2.3 30cm 5.19 1.58 3.3 40cm 5.36 1.23 4.4 50cm 5.47 1.01 5.4 60cm 5.49 0.84 6.5 70cm 5.55 0.73 7.6 80cm 5.57 0.65 8.6 90cm 5.58 0.57 9.9 100cm 5.64 0.52 10.9

These results above are extremely similar to my previous ones. I am therefore confident that the results are reliable as there is no obvious differ. I consider it necessary to produce a graph to display the results attained as it creates a clear delivery of data. Instead of making two graphs I have decided to unite the two sets of results to get an average as this will make a more accurate and precise graph. Here are the average resistances from my two results combined in a table:

Average Results table

 Length (cm) Resistance 1 (Ohms) Resistance 2 (Ohms) R1 + R2 (Ohms) Average Resistance (Ohms) 10cm 1.3 1.3 2.6 1.3 20cm 2.3 2.3 4.6 2.3 30cm 3.3 3.3 6.6 3.3 40cm 4.4 4.4 8.8 4.4 50cm 5.4 5.4 10.8 5.4 60cm 6.5 6.5 13.0 6.5 70cm 7.6 7.6 15.2 7.6 80cm 8.7 8.6 17.3 8.7 90cm 9.5 9.8 19.3 9.7 100cm 10.9 10.9 21.8 10.9

The first column records the length of the wire under investigation; the second column displays all the resistances from my first test. The third presents all the resistances from my second test. The fourth column demonstrates the sum of the second and third columns, combining the results. The final column shows an average of the two. This is accumulated by dividing the results in the fourth column by 2, as there are two sets of results. This provides the most specific resistance results. This allows me to produce a graph delivering the above results. These results support the theory that resistance increases as the length of wire increases. I repeated the test twice to confirm that the results were reliable and the exclusion of any anomalous results the combination of these results ensures they are dependable.  The graph clearly indicates that as the length of the wire increases the resistance increases. The furthest length used is 100cm and this length is also where the highest resistance exists.  The above graphs uses the most reliable results therefore the evidence extracted from the graph is correct. An example of this is the resistance at 10cm which is 1.3 Ohms where as the following measured length of 20cm has 2.26 Ohms which is an increase however demonstrates an un-proportional increases as energy loss occurs, this is as the resistance of a wire, under constant temperature conditions, is directly proportional to length. This graph shows the resistance in a 34 SWG Constantine wire. It shows measurements from 10cm up to 100cm. The resistance in the wire increases as the length of wire increases. My results do show that my hypothesis was correct. This is because in the preliminary experiment the thinnest wire gave us the widest range of resistance, as I predicted in my hypothesis. Furthermore in my actual experiment when we measured every 10cm along the 34 SWG Constantine wire. The resistance did increase when the wire increased. My graph is evidence to prove this. My line of best fit is showing a diagonal line going upwards showing the resistance increasing. If the line flowed diagonally downwards it would indicate the resistance had decreased. The line of best fit demonstrates a positive correlation.

With the use of precision and accuracy throughout the investigation I was able to obtain reliable results; this was continued throughout the entire experiment to ensure consistent and dependable results were extracted.

Conclusion

My hypotheses for both my preliminary and actual experiment were correct. The thinner the wire, the higher the resistance and the thicker the wire, the lower the resistance. This is because there are electrons in a circuit. These electrons travel around the circuit at an even pace. When they come to the wire placed in the circuit the electrons have to slow down in order to be able to pass through it. This causes a resistance. The electrons will collide together and the more they collide the higher the resistance of the wire. In a thin wire these electrons have to constrict tightly together in order to pass through, however in a thick wire these electrons do not have to constrict together as much to be able to pass through. After collecting my results I drew three graphs. The graph which compares the diameter of the wire to the resistance of the wire travels in a curve.

To conclude when I observed the results that I obtained I was able to discover that the Voltage (potential difference) increases slightly, whereas, the Amperes (current) decreased slightly. This corresponds exactly with my hypothesis. However, it was still more severe than the change of volts. On the graph it clearly displays that as the length increases so does the resistance. Several examples of this is the results at 40cm which was 4.38 Ohms and 60cm at 6.52 Ohms and 90cm at 9.65 Ohms. This replicates my prediction I stated earlier in my hypothesis. Reading from my line of best fit I can see that the resistance of the wire at 10cm is 1.30 Ohm’s and at 100cm (the end of the wire) and the end of my line of best fit, is 10.91 Ohm’s which shows an increase of resistance of 9.61 Ohms in total. This is evidence to prove my hypothesis is correct. This represents that when the wire was a shorter length it was easier for the electrical current to flow through it as it was less resisted. If the electrons are free to flow along there is less resistance. However the electrons would collide with each other and atoms in the material would cause them to lose energy. I believe this is the reason for the shorter wire producing light and a high quantity of thermal energy when I performed the experiment; this is an example of energy loss. This made me question why the resistance was higher in the longer wire if the shorter wire produced more energy. However I realised that the longer lengthened wire possessed the higher resistance therefore the product of the light energy effects the results.

Evaluation

I believe that this experiment was a great success. But on the other hand, there were many factors that could be improved if I was to ever do the experiment again. Such as, I think that the resources used to construct the experiment could be improved by using possibly newer and less depleted equipment. Because this could affect the accuracy of the readings and modify the end product. Therefore, if I was to do the experiment again I would improve the quality of equipment. However overall the equipment was good enough for the experiment and no obvious faults were noticeable in this particular experiment. Therefore in the experiment, I would measure the volts and amps more than once in my preliminary experiment to determine any anomalous results. This is to make sure the measurement is definitely correct. However I did follow this procedure in my main experiment which produced a more precise test. There were many methods, in which we done the experiment well. One example of this is that we used good safety procedures to prevent injury such as turning the power pack off when moving the crocodile clip around and avoiding the hot wires. But if I was to do the experiment again, I would expand it a little more by adding in another method to help explain and prove my hypothesis. I would do something such as, using different types of wire. This would help me to find out which material is the best conductor or resistor and therefore allows me to deduce different factors which affect resistance. Additional experiments would enable me to obtain the results to show if different types of wire would be the best conductors or resistors of electrical current and therefore make a deduction about which wires would be best suited for different components, therefore indicating the uses of different materials in wires such as steel which is used inside a filament light bulb, this gets hot where as copper is a good conductor and resists heat.  I have a reliable set of results as I undertook the experiment carefully and checked I was performing everything properly following my method exactly. A factor that could have affected the results given could have been thermal energy increase which could cause results to fluctuate. This is because as the wire gets hotter its resistance increases. However my results were reliable, this is evident as I conducted the test twice enabling me to produce a comparison of result. The results in my first and second tests were extremely similar therefore I can identify them as consistent. Another method I applied to produce an accurate test was that I allowed both the Voltmeter and Ammeter time to remain at a constant numerical reading. I did this instead of just recording the first measurement that appeared as it did alter slightly. I think if I did this experiment again I could adapt it to apply an strong enhancement by measuring the resistance as 1cm intervals to get extremely accurate results.

By Anna Hibben

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