Question

Give two examples of commercial generators. How is rotation of armature achieved in them? Explain briefly.

Hint:

Name hydroelectric and thermal generators. A turbine on the armature shaft is spun by falling water or by steam.

Answer 1

Step 1: Understanding the Question:
A commercial generator turns mechanical energy into electrical energy. The armature (coil) must keep rotating in the magnetic field to give a steady emf.
So the question asks for two real generators and for the source of the turning force in each.

Step 2: Example 1: Hydroelectric generator:
Water stored behind a dam falls from a height through a pipe. The falling water strikes the blades of a turbine and makes it spin.
The turbine shaft is joined to the armature, so the armature rotates in the field of the electromagnets.

Step 3: Example 2: Thermal generator:
Coal, oil or gas is burnt to boil water. The high-pressure steam hits the turbine blades and spins the turbine.
The same shaft turns the armature. (A nuclear power plant works the same way, but the heat comes from fission.)

Step 4: Why the rotation is needed:
Rotation changes the flux through the coil all the time. By Faraday's law this induces an emf \(e = NBA\omega\sin\omega t\).
If the armature stopped, the flux would stop changing and the emf would be zero.

Final Answer:
Two examples are the hydroelectric generator and the thermal generator. In both, a turbine driven by falling water or by steam keeps the armature rotating.