# Investigating Resistance of a Wire

Aim: The aim of the investigation is to find out what effect changing the length and thickness of wire has on resistance. Introduction: Resistance is any obstacle in a circuit that prevents or slows down the flow of electrons. Resistance is measured in ohms (â??) and the symbol is R. Electricity is conducted through a wire, by free electrons. The number of free electrons depends on the material. The higher the number of free electrons, the better the wire is at conducting electricity and therefore it has less resistance. The free electrons are given energy and as a result move and collide with neighbouring free electrons. When the electrons collide, they lose energy and create heat, which then results in the wire heating up. Resistance has an inversely proportional relationship with current. high current = low resistance low current = high resistance The resistance of a length of wire is calculated by using the ohms law. This is done by measuring the current present in the circuit and the voltage across the wire.
These measurements are then applied to the following formula: [image] To work out resistance this can be rearranged to: [image] This means that to work out the resistance you divide the voltage by the current. As you increase the current and voltage the resistance will increase too. The graph below shows what happens to the resistance when you increase the amount of amps and the amount of volts going through an ohmic conductor. In this graph the resistance is increasing at a steady rate. However, if we were using a filament lamp this would not happen. The graph below shows what happens as you increase the number of amps and volts passing through a filament lamp. As you can see the resistance increases steadily but then at the point marked (X) the resistance starts to increase faster. This is because the wire is beginning to get hot which will increase the resistance. Resistance can be affected by four different factors. These factors are:
Temperature
As the temperature increases the resistance increases therefore the current decreases. This is because the higher the temperature the faster the electrons move which cause more collisions. As the temperature decreases the resistance decreases therefore the current increases. This means that temperature has an inversely proportional relationship with current which is as follows: low temperature= low resistance = low current high temperature = high resistance = high current
Type of material
A wire that is good at conducting electricity will have a lower resistance. Therefore copper would be a good material to use as it is a good conductor of electricity and therefore will have less resistance. good conductor = low resistance poor conductor = high resistance
Thickness (cross-sectional area)
The thinner the wire, the higher itÂ?s resistance. This is because there is not much space for the electrons to pass through and therefore the electrons will collide with each other. This will cause more resistance and will also make the wire heat up. A thicker wire will have less resistance because the electrons have more space to flow and therefore will not collide with their neighbouring electrons. This will mean that the wire will stay cooler and also the electrons will not lose as much energy. To put it into perspective if there are ten people trying to walk through a narrow door at the same time, the people will have to push and fight to get through. By doing this they are losing energy and area also getting hot just like the wire does. If we have a bigger door the people will not use as much energy trying to get through. thin wire = high resistance thick wire = low resistance
Length
A longer wire will have more resistance because the electrons have a further distance to travel and therefore are getting hotter, which causes them to move faster and collide with neighbouring electrons. A shorter wire will have less resistance because the electrons are not moving as fast and are not losing as much energy. Electrons are a bit like people, the further we walk the hotter we get and the more energy we lose. longer wire = high resistance shorter wire = low resistance Therefore the best wire to use should have the following qualities:
low temperature
good conductor OF electricity E.G. copper
thick
short
Prediction: I think that as the length of the wire increases the resistance will increase too, I also predict that as the cross-sectional area of the wire decreases the resistance will increase. I think that the longest and the thinnest wire will have the most resistance. Therefore, I predict that the wire that is 25cm long and 36SWG will have the greatest resistance. The 18SWG wire that is 5cm long will have the least resistance. My reasons for saying this are because the longer amount of time electrons flows, the hotter they get which makes them move faster this causes collisions and increases the resistance. Therefore with a long wire the electrons will travel more and therefore more collisions will be caused with neighbouring particles, which means that the resistance will increase. This is why I think that the longer wire will have the highest resistance. The reason for me thinking that the thinner wire will have a greater resistance is because electrons are like people trying to fit through a small space. If there is a narrow space and a lot of people are trying to get through, people will push and lose energy. This is the same as electrons. If a lot of electrons try to get through a thin wire they will collide, lose energy, and cause resistance, However if there was a bigger space then the electrons would not lose energy. This is why I thought that a thicker wire will have less resistance. Plan: Fair testing: In my investigation I am going to change 2 variables. The 2 variables that I will be changing are: Â? The length of the Nichrome wire. I will increase this by 5cms each time starting from 5cm and going up to 25cm. Â? The cross-sectional area of the wire. I will use 3 different wires all of different thicknesses. I will use an 18 swg wire, a 24 swg wire and a 36 swg wire. To make my investigation fair I will:
Use a ruler to accurately measure the length of the wire each
time.
Keep the material of the wire the same. Always use Nichrome wire
which is an alloy of nickel and chromium.
Use the same 6v power supply.
Carry out my experiment 3 times to try and achieve accurate
results.
Keep the temperature of the wires the same by letting them cool down before doing my next experiment. Equipment: For my investigation I will need to use the following things:
Nichrome wire (thin-36 swg, mediumÂ?24 swg and thickÂ?18 swg)
Power supply (6V)
Ammeter
Voltmeter
Crocodile clips
Ruler
Connecting wires
Diagram: [image][image][image][image][image][image][image] 6v power supply Oval: A [image] [image] Ammeter [image][image][image][image] [image]Oval: V[image] Nichrome wire [image] Voltmeter Safety: I will take the following safety precautions: Â? Make sure that all stools are under a desk. Â? Make sure that the hot wires are cooled down before touching them. Â? Stay standing up when carrying out the experiment. Â? Not leave the power supply on for too long, especially when working with the thin wire to prevent it from burning. Method: 1. I will set up my equipment as shown in the diagram. 2. I will gather 3 Nichrome wires of various lengths (thin ? 36 swg, medium Â? 24 swg and thick Â? 18 swg.) 3. I will first connect my crocodile clips to one end of the 36SWG wire and the other crocodile clip 5 cm away which will mean that the wire has a length of 5 cm. 4. I will then switch on the power supply 5. I will note down the current from the ammeter and the voltage from the voltmeter. 6. I will then move my crocodile clip 5 cm along to make my 10 cm long and I will record the current and voltage. 7. I will repeat step 6 for a wire of length 15 cm, 20 cm and 25 cm. 8. I will repeat steps 3, 4, 5 and 6 for the 24 swg wire. 9. I will repeat these steps again for an 18 swg wire. 10. By this time the thinnest wire will have cooled down and therefore I will repeat the experiment three times to ensure that my results are accurate. 11. I will display my results in a table 12. I will then work out the average current and voltage for each variable. 13. I will then work out the resistances. 14. From this I will be able to draw a graph which will help me to analyse my results. Results Thickness of Wire = 18 swg Length (CM) Current (I) (A) Voltage (Volts) (V) Resistance? (â??) Exp. 1 Exp. 2 Exp. 3 Average Exp. 1 Exp. 2 Exp. 3 Average 5 1.17 1.18 1.16 1.17 0.09 0.09 0.10 0.09 0.08 10 1.16 1.16 1.17 1.16 0.15 0.16 0.15 0.15 0.12 15 1.17 1.18 1.17 1.17 0.22 0.20 0.21 0.22 0.19 20 1.15 1.17 1.17 1.16 0.29 0.28 0.27 0.28 0.24 25 1.16 1.15 1.16 1.16 0.34 0.32 0.32 0.32 0.25 Thickness of Wire = 24 swg Length (CM) Current (I) (A) Voltage (Volts) (V) Resistance? (â??) Exp. 1 Exp. 2 Exp. 3 Average Exp. 1 Exp. 2 Exp. 3 Average 5 1.14 1.13 1.14 1.14 0.33 0.35 0.32 0.33 0.29 10 1.12 1.12 1.13 1.12 0.81 0.77 0.88 0.82 0.73 15 1.13 1.16 1.14 1.14 0.93 0.87 0.94 0.92 0.81 20 1.10 1.16 1.12 1.13 1.23 0.18 1.12 1.18 1.04 25 1.08 1.09 1.09 1.09 1.40 1.42 1.40 1.41 1.29 Thickness of Wire = 36 swg Length (CM) Current (I) (A) Voltage (Volts) (V) Resistance? (â??) Exp. 1 Exp. 2 Exp. 3 Average Exp. 1 Exp. 2 Exp. 3 Average 5 1.14 1.14 1.15 1.14 1.18 1.30 1.25 1.25 1.09 10 1.06 1.07 1.09 1.07 3.47 3.45 3.47 3.81 3.57 15 0.91 0.92 0.97 0.93 4.44 4.25 4.33 4.30 4.62 20 0.77 0.79 1.01 0.86 5.12 4.76 4.95 4.96 5.77 25 0.66 0.65 0.66 0.66 5.52 5.40 5.46 5.47 8.29 Conclusion: After examining my results and graph I found that my prediction was correct. The longer (25 cm), narrower wire (36 swg) had the greatest resistance and the shorter (5 cm), and thicker wire (18 swg) had the least resistance. The reason that the thinner wire had a greater resistance is that there was less space for the electrons to flow through, which caused the electrons to collide with each other. These collisions make the electrons lose energy and increase the resistance. The thicker wire had more space for the electrons to flow and therefore there were fewer collisions which meant that less energy was lost. The longer wire had more resistance because the electrons had to travel a further distance and therefore the heat was increasing. When the heat in the wire increased the electrons would have began to move faster which would cause them to collide with other electrons which resulted in lose of energy and an increase in resistance. In the shorter wire the electrons did not have to travel as far and therefore the wire did not heat up as much, which meant that the electrons did not lose as much energy.

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