Surface Tension By Capillary Rise — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Surface Tension by Capillary Rise Used to determine the surface tension of a liquid that wets or partially wets a narrow bore glass tube. Equating the upward vertical component of surface tension force (2 pi r T cos(theta)) to the weight of the liquid column (pi r 2 h rho g) Solving for T: T = (r h rho g) / (2 cos(theta)) The tube must be a true capillary (narrow bore) The tube must be chemically clean The temperature must remain constant during the experiment Forgetting that 'h' should be measured from the lower meniscus for wetting liquids Ignoring the weight of the liquid in the meniscus (corrected formula uses h + r/3) Assuming theta is always zero (it is only nearly zero for pure water and clean glass)