Question

In determining the surface tension by capillary rise method, why would the taking of a difference of two heights be better than just taking a single height?

Answer 1

ANS . Surface tension is given by the formula

    Where is the angle between the liquid maniscus and the glass and r is the radius of the curvature.h is the height of rise of liquid.

When h is taken twice of it's initial value, the force of gravity is doubled because we know that F = mgh . So the maniscus experiences more force of gravity which pulls it downward and the angle becomes very less. The maniscus becomes more prominently circular.

When we determine surface tension we neglect the cos value which affect the precision of Surface Tension value. When , due to increase in height, becomes very less, it can be neglected and the curvature can be neglected as well, giving more precise and accurate value of surface tension rather than when it is larger.