Question

When liquid medicine of density rho is to be put in the eye, it is done with the help of a dropper. As the bylb on the top of the dropper is pressed. A drop frons at the opening of the dropper. We wish to estimate the size of the drop. We first assume that the drop formed at the opening is spherical because that requires a minimum increase in its surface energy, To determine the size. We calculate the net vertical force due to the surface tension T when the radius of the drop is R. when this force become smaller than the weight of the drop the drop gets detached from the dropper. After the drop detaches, its surface energy is

Answer 1

Given: Surface Tension = T

Radius of the drop = r

To Find: The surface energy of the drop

Solution:

Vertical force due to surface tension -  

Fv = Fsinθ,

Thus,  

= (T)(2πr)(r/R)  

= 2πr²T/R

Force due to surface tension = Weight of liquid in the drop

= T2πr = 4/3πR³

Substituting the values -

R = 2.0×10³ m

Answer: The surface energy of the drop is 2.0×10³ m