Power Systems
The draft tube is provided to

 reduce the effect of water hammer.
 raise the water surface of the stream to create an artificial head.
  increase the acting head on the water wheel.
None of these

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Power Systems
Gross head of an hydroelectric power station is

 all of above.
 the height of water level in the river where the storage is provided.
 the height of water level in the river where the tail race is provided.
  the difference of water level between the level in storage and tail race.

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