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Renewable Energy

Science brain teasers require understanding of the physical or biological world and the laws that govern it.


Puzzle ID:#15992
Fun:*** (2.42)
Difficulty:** (1.29)
Submitted By:curtiss82*****




For his science fair project, John decided to experiment with renewable energy sources. He hoped that his work will solve all of our energy problems. He decided to power a generator with an electric motor. He thought once the generator was up to speed, he could just flip a switch and the generator could supply the electricity that powered the electric motor. John was for sure he made a historical discovery, he found an alternative to fossil fuels. His energy source was purely renewable. Why did his experiment fail once he put it to the test?


Even if the generator and electric motor were 100% efficient, his set up would still not work. The maximum amount of electrical power that the generator can supply is equal to the mechanical power that the electric motor provides. So once the generator powers the electric motor, there would be no power left to run any additional electrical appliance. If it worked it would be breaking the Conservation of Energy Law; he would be making energy out of nothing. In reality, neither the motor nor the generator are 100% efficient. The generator doesn't convert all of the mechanical power to electricity and the motor doesn't convert all of the electrical power to mechanical power. A lot of the power is lost as heat. So in reality, besides not being able to power any additional appliances, the generator and motor would stop running after a short period.

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