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.
If the radius of the opening of the dropper is r, the vertical force due to the surface tension on the drop of radius`R`(assuming `rlt ltR)` is
A. `2pi rT`
B. `2pi RT`
C. `(2pir^(2)T)/(R)`
D. `(2piR^(2)T)/(r)`

Answer 1

Vertical force due to surface tension,
`F_(v)=F sin theta `
`=(T)(2 pi r)(r//R)`
`=(2 pi r^(2) T)/(R )`
`:.` Correct option is (c ).