Question

12. Your friend with great excitement tells you about his newest idea to solve the energy crisis: He wants to use an electromotor to drive a generator and then use part of the electric power generated to power the electromotor while using the rest to power his home. What would you tell him?

Answer 1

This idea is a very inefficient method of producing electricity.

Let me explain why:

As a person who knows physics, you must be very aware of Law of conservation of energy and it's applications.

Law of conservation of energy states that energy can neither be CREATED nor be DESTROYED.

That means, energy can only change from one form to another.

Here, when he uses an electric motor to power a generator, the electric energy produced from the motor is converted into mechanical energy.

Let's say X amount of energy is produced by motor and it is completely transferred into mechanical energy for powering generator (neglect heat, sound, friction and such energy loses).

Now generator has X amount of mechanical energy. Assuming that generator is 100% efficient, this X amount of mechanical energy will be converted into electrical energy by generator.

Now this is our generated electricity = X.

Some amount of electricity generated out of X will be used to power your friends how. So now the remaining amount of energy which is very less than X, will be gone back to the electric motor and it again uses this remaining energy to do mechanical work and so on.

Hence, some energy is used for house old purpose, and left is used for generation of electricity again.

This cycle will go on until the energy X becomes zero at some point.

So this method is inefficient since there is no external source for additional energy. (because energy can not be created)

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