Preliminary 2 The Changing Length Experiment example essay topic

Physics Course Work Aim: The aim of this physics coursework is to find out the electrical resistivity of constantan by changing different variables. Factors that I will change or keep the same: Thickness of the wire Length of the wire The type of wire (copper, aluminium ect) Thickness: Keep length and the wire the same. Length: Keep the thickness and the material the same. Material: Keep the length and thickness the same. Predictions: I predict that the resistance will grow as we increase the length of the wire. The cause of resistance is friction between two materials or moving objects.

For a good circuit to work the resistance must be low, especially the wires that connect the components. Resistance is where electrons give up the potential energy they carry from the battery. Resistance causes electrical energy to change into other forms, such as light and heat. If a lamp filament had 0 resistance then no energy change could occur and then no light / heat would be given off.

A conductor's resistance depends on two things: 1. Its dimensions 2. The material of which it is made I believe that if the wire is thinner than the resistance is higher and a long wire has greater resistance than a short one. The material the wire is made of would also effect my prediction; it was made of constantan which means that temperature does not affect the resistance.

I have done something similar do this in class, we have done parallel and series circuitry which can be compared to this coursework because of the experiments that we did: 1st preliminary we did was a series. 2nd preliminary we did was a series. I decided to use a series circuit for the actual experiment. Preliminary experiments: I will do two preliminary tests because this will enable me to decide if the way I am conducting my experiment is practical, safe and viable, it will also help me with my plan because it will enable me to decide how to decide how to set it up and which equipment will be the most practical to use etc. Preliminary experiment 1: For my first preliminary experiment I have decided to change the thickness by looping the wire over itself in 10 cm lengths.

This would mean it is a parallel circuit. Wire thickness Amp's (A) Voltage (V) Resistance ( ) 1 length over 10 cm 1.20 0.82 0.68 2 lengths over 10 cm 1.92 0.58 0.30 3 lengths over 10 cm 2 0.42 0.21 4 lengths over 10 cm 2.20 0.37 0.17 Results for 1st preliminary: I have decided that this way of doing the experiment would take a long time to accomplish so I for my second preliminary I will be changing the length. Prediction revised: When I change the length of the wire, I predict that the resistance will go up. I believe this is true because the longer the wire the higher the Voltage drop.

Preliminary experiment 2: For the second preliminary I will change the length and keep the material and thickness the same. This means it is a series circuit. Results for Second preliminary: Length of wire (m) Amp's (A) Voltage (v) Resistance (Ω ) 10 cm 0.53 0.38 0.72 20 cm 0.37 0.53 1.43 30 cm 0.3 0.6 2 40 cm 0.25 0.65 2.6 50 cm 0.21 0.7 3.3 60 cm 0.18 0.74 4.1 70 cm 0.16 0.76 4.75 80 cm 0.13 0.78 6 90 cm 0.12 0.80 6.6 100 cm 0.12 0.81 6.75 The preliminary work that I have just done has helped me to do decide which experiment is the easiest to do and which one will give me more accurate results this was - preliminary 2 the changing length experiment. This is because it was easier to perform and fewer things went wrong unlike the 1st preliminary - the experiment which involved looping the wires over, this experiment was tricky to keep the wires in the same place and also keeping them taught was very challenging. Plan: For my actual coursework I will be doing the length experiment to find out my prediction revised is correct. The equipment I will use will be: 1 x power pack 1 x Ammeter 1 x Voltmeter 5 x lead 1 x metre rule, 1 x cello-tape 1 meter of constantan wire 0.32 mm (the resistance will not change with the application of heat) 2 x crocodile clips.

V I first took the apparatus (shown above) and assembled them into a circuit as shown on Page 3. I made sure to use the power pack at 2 volts for each of the readings otherwise the wire would melt if the voltage was any higher say - 8 vs. This is dangerous as some could hurt themselves on the hot wire and is also impractical for the experiment. To get my results I had to first make sure that the two crocodile clips were holding the wire exactly 1 meter apart and then took the readings from both the Voltmeter and the Ammeter. Next I changed the distance of the crocodile clips to 10 cm apart and took the readings, then 20 cm, 30 cm, 40 cm and so on. I did this until I arrived at 100 cm giving us 10 different results for the wire each time making sure that the distance between the clips was as accurate as possible. Once I had acquired all of my readings for the first experiment I went on to repeat the experiment 2 more times to get 3 sets of results (I did this is one lesson to make sure what we did was a fair test, i.e. we used the same apparatus etc.) This is the circuit I will use.

Certain factors could effect how the results come out, such as... Variable: Elucidation: Type of power pack Use the same power pack for all experiments to make sure of a fair test. Ammeter Use the same ammeter for all 3 times for fair test. Voltmeter Use the same voltmeter for all 3 times for fair test. Leads Use the same leads for all 3 times for fair test. Length of wire Use the same metre rule to measure where to put the clips for fair test.

Type of wire Use the same wire all 3 times (Constantan 0.32 mm) for a fair test. Procedure I will complete all the experiments in the same manner as the fist one. I will try to do all three experiments in one lesson so that I don't have to worry about using different apparatus. I will be investigating how the resistance of a wire changes when the length is varied. I will measure the amps and volts going through the circuit, I will take 10 readings and the range will be in sets of 10 cm e.g. I will take results at 10 cm, 20 cm so on till I get to 100 cm and I will do this three times and take the average of all three experiments to work with.

I will need to do some calculations such as working out the resistance. For this I will use... Resistance = Voltage R = V Current I I will make sure my experiment is safe by having the equipment checked and passed before I use it, I will also listen to any safety advice given by the teacher and I will act upon it. Fair test: To make this a fair test I will...

Use all the same equipment (including power pack and measuring implements) Use the same method for all the experiments (the one explained above) Use the same set-up all three times (the one illustrated above) Use the same wire (constantan 0.32 mm) Do all three experiments in the same lesson The experiment: After doing the same experiment three times these are the results I ended up with. Analysing the results: From a look at my graph I can tell that the as length of the wire increases so does that resistance; this makes the length of the wire directly proportional to the resistance of the wire. e.g. Resistance = 0.69Ω Length = 0.1 m Resistance = 1.32 Ω Length = 0.2 m Resistance = 2.12 Ω Length = 0.3 m The results that I have support my prediction that when I change the length of the wire I predict that the resistance will go up. This is because metal wires conduct electricity; because metals have free electrons (which carry a negative charge) this allows the free electrons to conduct electricity, carrying a negative charge enables the free electrons to jump along the line of atoms in a wire. Resistance is caused when these electrons flowing towards the positive terminal have to 'jump' atoms so the more atoms the electrons have to 'jump' the higher the resistance Finding out the resistance of the wire: I will use the formula: R = f L a to work out the resistance of a wire.

Working out Area: a stands for the area of the wire. I used 0.32 mm diameter constantan in this experiment but I need to work everything out in meters so we need to divide this number by 1000. I also need to divide it by 2 to get the radius 0.32 m: 1000: 2 = 1.6 x 10-4 m Radius = 1.6 x 10-4 m The equation for working out the area is R^2 - I will now use this equation to work out the area. x (1.6 x 10 -4) 2 = 8.042477193 x 10-8 m^2 So the area of constantan is... a = 8.042477193 x 10-8 m^2 The formula R = f L can be re arranged to read R = f a L a By dividing by L Gradient R can be worked out by calculating the gradient of the graph. L The change in Y (average resistance in ) over the change in X (length of wire in m) The range of average resistance (Y) (R) = 0.69 6.33 so the change = 5.64 m The range of the length of wire (X) (L) = 0.1 1 so the change = 0.9 m R = 5.64 m = 6.267 m^2 L 0.9 m Now the equation looks like this 6.267 m^2 = f so now I need to make f the a subject of the formula by x the whole equation by a, so we get... a x 6.267 m^2 = f a = 8.0424 x 10-7 m^2 (8.0424 x 10-8) X 6.267 = 5.040 x 10-7 m f = 5.040 x 10-7 m f = the electrical resistivity of the wire In the book Science Book Data by Oliver and Boyd it states that the actual electrical resistivity of constantan is 4.9 x 10-7 m so my calculation through using the results I collected was not far off (Only by 0.14 x 10-7 m which is not very much). Evaluation: The method I used was a sensible way of testing my prediction because it was logical and it worked, it is also easy to follow it was simply set up as well.

If I was to do this experiment again I would consider using more up to date and precise equipment I would also test this equipment before using in my experiment I would also record my results to 3 to 4 decimal places for more accurate results. I would not use any other different equipment because the equipment I used for the experiment suited my purposes for the tests, I would also not use the equipment in another way. I would have liked to take another 2 readings so that I could be as accurate as possible but as my time was limited this was not possible, there were a few abnormal readings but these results are within the bounds of experimental error. I could have also tested the resistance of the wires I used as these might have affected my results giving me the 0.3795 x 10-7 error that I gained from the experiment.