If a centrifugal pump has an impeller speed of N (in rpm) discharge Q (in m3/s) and the total head H (in m), the expression for the specific speed Ns of the pump is given by

• A. \({{\rm{N}}_{\rm{s}}} = \frac{{{\rm{N}}{{\rm{Q}}^{0.5}}}}{{{{\rm{H}}^{0.5}}}}\)
• B. \({{\rm{N}}_{\rm{s}}} = \frac{{{\rm{N}}{{\rm{Q}}^{0.5}}}}{{\rm{H}}}\)
• C. \({{\rm{N}}_{\rm{s}}} = \frac{{{\rm{N}}{{\rm{Q}}^{0.5}}}}{{{{\rm{H}}^{0.75}}}}\)
• D. \({{\rm{N}}_{\rm{s}}} = \frac{{{\rm{NQ}}}}{{{{\rm{H}}^{0.75}}}}{\rm{\;}}\)