The efficiency of an eElectric motor Essay Example for Free

The efficiency of an eElectric motor Essay The efficiency of the motor in experiment 2 does decrease linearly with increasing mass as I predicted. Ideally the two graphs should follow each other since I used the same motor in each experiment. However from my graph you can see that my calculated efficiency for the second experiment is consistently about 9% higher than the calculated efficiency from my first experiment. This difference has probably been caused by the inaccuracy of the joule meter. This is inconsistent with my results from my calibration experiment. They showed that the joule meter always records more energy that it is receives and therefore if I correct my results for experiment 2 it would make the motor even more efficient. However the linear sections of the graphs have the same gradient and this shows that in both experiments the efficiency is varying in the same way. Extension: Aim: To measuring the efficiency of the electric motor as a generator and to establish if the system is time reversible. The experiment: See Diagram for circuit digarm. Experimental method: I will dropped a variety of weights a distance of 1. 12m and then I recorded the amount of electrical energy produced by the motor using the joule meter Acknowledged Errors 1. The inaccuracy of the joule meter-however I can use my calibration curve to correct for this 2. Friction in the pulley system 3. The weight has kinetic energy when I hits the ground and this energy is lost from the system thus reducing the efficiency of the generator. My Results: H=1. 12m load=10. 3 ohms Mass (kg) Average Time for full drop(s) Joules recorded Exp1x10 Joules recorded Exp2x10 Average number of joules recordedx10 %E. Energy Input (J) Graph: Explaining the graph: The energy I put in the generator is dissipated in three ways. 1. Useful energy is dissipated in the load 2. Energy is lost in the friction of the pulley system 3. When current flows through the internal resistance of the motor energy is lost 4. Energy is lost when the weight I drop hits the flaw It follows that because energy is conserved: The Potential energy of the weight= Power dissipated in load + Work done against friction +Energy Lost in the motors resistance +Energy lost as the weight hits the floor M=mass, I=current, F=friction force, R=resistance, V=final speed of weight In my analysis I have chosen to ignore the energy lost in the internal resistance of the motor. This is sensible since the energy lost in the internal resistance was insignificant compared to the energy lost in the load. To further simplify things I will also ignore the energy lost as the weight hits the ground. This factor was very small because my weights travelled quite slowly and they had small masses. Simplified formula for analysis: Efficiency If you assume that the work done against friction is constant this formula explains the 1-1/x form of my graph. For small weights the generator is inefficient since most of the weights potential energy is being used to overcome friction. For small the second term of the formula is large and the generator is therefore inefficient. This is shown by my graph. For large weights the work done against friction becomes insignificant and consequently the generator becomes more increasingly more efficient. For larger the second term would tend to zero and the efficiency should tend to 100%. My results do show that the efficiency increases for heavier weights however my results appear to approach an efficiency of 14% not 100%. This difference may be caused by the fact that for my larger weight the energy lost in the motors resistance and the energy lost as the weight hit the floor become significant. The inaccuracy of the joule meter may have also contributed to this difference. Is a the motor time reversible If my motor was time reversible it should behave in the same way irrespective of the direction of time. For example if you use electrical energy lift a weight with a motor if the system is time reversible you should be able to get the electrical energy back by dropping the weight. A motor is obviously time reversible to an extent since it can be used both as a motor and a generator. However my results show that for my experiment you are only able to retrieve a small fraction of the energy you used lifting when using the motor as a generator (about 2. 5 joules out of 150 or 2%). This inefficiency can be partially explained by considering the parts of the system that are not time reversible. This includes the friction in the system and the energy lost in the internal resistance of the motor. Here energy is lost as heat and sound that cannot be retrieved. Conclusion: In general my experiments went well and I was able to use my result to make some useful conclusions. I was very pleased with the accuracy of my results. If I had more time I would have taken more experimental reading so that I could get a more complete picture of what was happening. I would also have spent more time calibrating the joule meter since its inaccuracy had a large effect on my results. Bibliography: Sources used: 1) Nuffield Advanced Science Physics student guide 2 unit H to L, Published by Longman, ISBN=0-582-35416-1 2) Web page: Motors URL=www. srl. gatech. edu/education/ME3110/design-reports/RSVP/DR4/Motors. http 3) Encyclopaedia Britannica CD-ROM 4) Encarta 99 CD-ROM by Microsoft 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.