Question

What is the formula of capillarity?

Answer 1

1. It is a fact that when a tube of a small radius is dipped in a liquid the height of the liquid rises or decreases. The tube is called a capillary tube and this phenomenon is called capillarity.
2. The formula for this height is called a capillary formula.
3. The formula is obtained when we do all the force analyses on the liquid. Depending on the force of attraction between the tube surface and liquid molecules, the liquid acquires a shape as shown below. The angle made by the liquid edge with the vertical tube plane is called the contact angle. It is denoted by $\theta$.
4. We get the formula as $h=\frac{2S\cos \theta }{r\rho g}$
   Here, $h$ is the height of the liquid raised or decreased, $S$ is the surface tension of the liquid, $r$ is the radius of the capillary tube, $\rho$ is the density of the liquid.