GENERATING ELECTRICITY.



                        
A motor is a device for transforming electrical energy into mechanical [kinetic] energy. To generate electricity, we need a device that will do the opposite: it must transforms mechanical energy into electrical energy. Fortunately, we can simply use an electric motor in reverse. If you connect up an electric motor  to a meter and spin its axle, the meter will show that you have generated a voltage.    
Inside the motor, the coil is spinning around in the magnetic field provided by the permanent magnets. The result is that a current flows in the coil, and this is shown by the meter. We say that the current has been included, and the motor is acting as a generator.
       
     There are many different designs of generator, just as there are many different designs of electric motor. Some generate direct current, others generate alternating current. Some use permanent magnets, while others use electromagnets. If you have a bicycle, you may have a generator of a different sort - a dynamo - for powering the lights.

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The power station shown generators shown in the figure generate alternating current at a voltage of about 25kV. The turbines are made to spin by the high-pressure steam from the boiler. The generator is on the same axle as the turbine, so it spins too. A coil inside the generator spins around inside some fixed electromagnets, which provide the magnetic field. A large current that the power station supplies to consumers. A fraction of it is used to supply the electromagnets of the generator itself. 
All of these generators have three things in common:
  • a magnetic field [ provided by magnets or electromagnets]
  • a coil of wire [ fixed or moving ]
  • movement [ the coil and magnetic field move relative to one another].
When the coil and the magnetic field move relative to each other, a current flows in the coil if it is part of a complete circuit. This is known as an induced current. If the generator is not connected up to a circuit, there will be an induced e.m.f [ or induced voltage] across its ends, ready to make a current flow around a circuit.

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