Correct option is C
The specific speed (N_s) of a hydraulic turbine is a dimensionless parameter that characterizes the shape and performance of the turbine. It is defined as the speed at which a geometrically similar turbine would operate to produce unit power under unit head.
The specific speed ranges for different turbines are:
· Pelton wheel (Impulse turbine): Low specific speed (typically 10–60 rpm)
· Francis turbine (Reaction turbine): Medium specific speed (typically 60–400 rpm)
· Kaplan turbine (Reaction turbine with adjustable blades): High specific speed (typically 300–1000 rpm)
