The rate of a chemical reaction Essay Example for Free

The rate of a chemical reaction Essay The equation for resistance using resistivity is Resistance = resistivity x length / area of cross section of the wire The resistivity of Nichrome at 250C is 100 x 10-8 ohm-m. The radius of the wire isResistance = resistivity x length / area of cross section of the wire Resistance = 100 x 10-8 x 0. 4m / 6. 16m2 x 10 -8 Resistance = 6. 49 ? rounded 2 d. p. TPlan Aim I aim to find out if the length of a Nichrome wire affects the resistance. Safety To ensure this experiment is safe I will:  Ensure that the power pack does not exceed 2 volts in case the wires overheat.    I will also only leave the power pack on for short amounts of time so the wire does not overheat. I will not perform the experiment in a wet area because water is a very good conductor of electricity and so this would be very dangerous.   I will not touch the wire once the power pack is switched on because the current will heat up the wire. Factors to control The independent variable will be: 1 The amount of resistance in different lengths of wire. The variables that I will keep the same will be: 2 Width of wire- I must keep the wire a thickness of 32SWG. If I change the width of the wire the resistance will change because there is more resistance in a thicker wire because there are more fixed ions so there are more collisions in the wire and more successful collisions means the resistance will increase 3 Material of wire- different materials will affect the amount of free electrons that are able to move through the wire. If there are more or larger atoms then there will be more collisions. This causes the voltage of the wire to increase causing a higher resistance. Also if the atoms in the material are more closely packed then the electrons will have more frequent collisions and the resistance will increase. I will use Nichrome only. 4 Density of wire- In a higher density wire there will be a higher resistance because there will be more fixed ions and more collisions. 5 Temperature of wire- If the wire is heated up the atoms in the wire will start to vibrate because of their increase in energy. This causes more collisions between the electrons and the atoms as the atoms are moving into the path of the electrons. This increase in collisions means that there will be an increase in resistance. 6 Shape of wire- the wire will be straight and taped to a meter rule, the shape of the wire may increase the resistance. 7 Voltage of 2 volts- I will have to keep a constant voltage because if the voltage changes then the resistance will change. The equation for resistance = voltage / current. If voltage increases, resistance increases. Apparatus The apparatus I will need to perform this experiment will be: 1 Power pack (2volts) 2 Ammeter 3 Voltmeter 4 6 wires 5 2 crocodile clips 6 Meter rule 7 Masking tape 8 Board marker Circuit diagram Method I have chosen to take a range of 10 lengths. I have chosen a range of 10 as to plot an accurate graph I will need at least 10 points to mark on the graph. The lengths that I have chosen are as follows: 10cm, 20cm, 30cm, 40 cm, 50cm, 60cm, 70cm, 80cm, 90cm and 100cm. I have chosen these lengths because the meter ruler can easily measure them and enough results to make a firm conclusion. To change the length of the Nichrome wire during the experiment I will tape down 1 meter of Nichrome 32 swg wire to a meter rule. I will then connect the 2 crocodile clips different distances apart using the measurements on the meter rule. The wire will be attached at X in the circuit. In my experiment I will find the current in the circuit using an ammeter and I will find the voltage in the wire using a voltmeter. I will take these two readings so I can then calculate the resistance using the equation resistance = voltage / current. I want to make my experiment as accurate as possible so I want to produce repeat readings so that I can find an average resistance. I will be using a variable resistor in my experiment to produce these repeat readings. I will draw 4 equally spaced points on the variable resistor with a board marker. To get my repeat readings I will move the variable resistor to these 4 points and get four readings for each length. After I have found the average resistance for each length of wire I will produce a graph showing the average resistance against the length of the wire. I will draw on my graph a line of best fit and then from this I will be able to see if my prediction was correct and if the resistance does increase when the length of wire increases. 1. Set up a circuit as shown above. Set the power pack at a constant voltage of 2 volts. 2. At X in the circuit the wire will be placed. I will first connect the crocodile clips 100cm apart. Then turn the voltmeter and ammeter on and ensure the variable resistor is set at the first point. 3. Now turn on the power pack and record the first results shown on the ammeter and voltmeter. I must take the first results because the results may change due to overheating if the power pack is left on. Now turn off the power pack. 4. To take my repeat reading of 100cm I will then move the slider on the variable resistor to the second marked point. I will now turn on the power pack and record the first result shown on the ammeter and voltmeter. 5. I will continue taking my repeat readings and moving the variable resistor along and recording the results for 100cm. 6. I will then change the length of wire to 90cm by moving the crocodile clips and i will set the variable resistor at the first point. Then I will turn on the power pack and record the first set of results. I will take 4 repeat readings for each length of Nichrome wire. 7. I will record 4 repeat readings for each length of Nichrome wire until I have results for all 10 lengths. Results table Length (cm) Repeat number Voltage (volts) Current (amps) Resistance (? ) Average 17. 82 I have put in bold any anomalous results. Analysing and considering evidence Conclusion From my graph I can tell that my prediction was correct. As the length increases the resistance increases, a piece of 20cm wire has a resistance of 3.8 ? and a piece of 30cm wire has a resistance of 5. 6 ?. This is because a longer piece of wire has a higher resistance because in a longer piece of wire there are more collisions between the electrons and the metal ions. In every successful collision energy is lost from the electron to the wire ions. The result is that the voltage of the wire increases. Because the equation for resistance is resistance = voltage / current, the resistance then increases. From my line of best I can also tell that as the length doubles the resistance always almost doubles too. A piece of 20cm wire has a resistance of 3.8 ? and a piece of 40cm wire has a resistance of 7. 4 ?. Double 3. 8 ? is 7. 6 ? this is almost double but not quite probably because my experiment was not quite accurate. A piece of wire 30cm long had a resistance of 5. 6 ? and a piece of wire 60cm long has a resistance of 11. 1 ?. This is also almost double, double 5. 6 ? is 11. 2 ?. The resistance doubles as the length doubles because there can be double the amount of successful collisions so double the amount of energy is lost causing the voltage to double and so the resistance doubles. Key Electron Metal ion Predicted results Length (cm) Predicted resistance ( ? ) Actual resistance ( ? ) Difference (ll of my results were quite close to my predicted results but as the length increases my predicted resistances become less accurate. This could have been for several reasons that are mentioned in my evaluation but probably as my experiment went on the wire overheated so my results became less accurate. Evaluating My method of collecting my results worked quite well. I gained the results I expected from my experiment. The quality of my evidence was good. My line of best fit went through almost all of my points on my graph and was quite similar to my predicted line of best. I did have some anomalous results. When I experimented with 10cm of Nichrome wire my fourth repeat readings was quite different to the other readings. It had a resistance 0. 87 ? that was the lowest repeat readings for 10cm. The second lowest was 1. 80 ? , this is quite a lot more than the anomalous result. When investigating which 30cm of Nichrome wire I had another anomalous result that was 6. 48 ? , the third repeat reading. This was the biggest repeat reading. The second largest was only 5. 89 ?. This could have been because: I left the power pack on too long. This causes the wire to overheat.   When I was measuring the lengths of the Nichrome wire my measurements might have been slightly inaccurate. The rulers used might not have been exact and it was difficult to get an accurate reading of length by eye as the wire was not completely straight. Also the ruler may have been of different thicknesses throughout the length. This would have contributed as a slight error in my results.   The ammeter and voltmeter could have been slightly faulty and not given me correct, accurate readings.   I connected the wire into the circuit using crocodile clips. These were quite loose and so this could have made my results less accurate. If I improved my method I could either attach the wires with tape but this may affect my results so instead I could solder the Nichrome wire into my circuit. It was difficult to adjust the variable resistor slider accurately only by eye. If I did the investigation again I could try to and adjust the variable resistor accurately I will use an advanced digital variable resistor.   I also found it difficult to measure exact lengths against the meter rule because the crocodile clips didnt clip on to the wire very securely. If I did the investigation again I could pre cut all the lengths of wire before the experiment instead of just connecting the crocodile clips at different distances apart on the meter rule. To further my investigation I could use the same method but increase the range of lengths. I could use lengths of up to 3 meters. I could take readings from lengths at smaller intervals; I could take reading every 5cm instead of every 10cm as I did. I could also take more repeat readings to get a even more accurate average. Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.