For a liquid flowing in a pipe where cross section area changes from A1 to A2 and velocity of flow changes from v1 to v2, then A1 × v1 = A2 × v2 is called _________.

CONCEPT:Equation of Continuity: In a time Δ t, the volume of liquid ENTERING the tube of flow in steady flow is A1V1 Δ t. The same volume must flow out as the liquid is incompressible. The volume flowing out is A2V2 Δ t.Here,A1 and A2 = Area of the cross-section of the tube at point 1 and 2 respectively v1 and v2 = velocity of the FLUID at point 1 and 2 According to the equation of continuity⇒ A1V1Δ t = A2V2Δ t⇒ A1V1 = A2V2 = constantWhere, A = area of cross-section, V = speed of the fluid, t = time intervalEXPLANATION:From the above, it is CLEAR that for a liquid flowing in a pipe where the cross-section area changes from A1 to A2 and velocity of flow changes from v1 to v2, then A1 × v1 = A2 × v2 is called equation of continuity. Therefore option 4 is correct.