If A denotes the area of free surface of a liquid and} the depth of an orifice of area of cross-section o below the liquid surface then the velocity r of flow through the orifice is given by

Applying Bernoulli's theorem, the rate off low from surface to orifice is given byP+12ρv′2+ρgh=P+12ρv2+0 where v' = velocity of all surfacses of liquid. If v is velocity of efflux, then Av′=av  or  v′=(av/A) From eqs. (1) and (2), we 8et 12ρavA2+ρgh=12ρv2 or  v2−a2v2A2=2gh V=2ghA2A2−a21/2