If two glass plates have water between them and are separated by very small distance (see figure). It is very difficult to pull them apart. It is because the water in between forms cylindrical surface on the side that gives rise ot lower pressure in the water in comparison to atmosphere. If the radius of the cylindrical surface is `R` and surface tension of water is `T` then the pressure in water between the plates is lowr by:

Options

A. `(2T)/(R)`
B. `(4T)/(R)`
C. `(T)/(4R)`
D. `T/R`

Answer

A

Explanation

Let radius of meniscus is `r_(1)` inside the cylinder and `r_2` is the radius of meniscus that touched the curved surface area of cylinder.
Here excess pressure, `P_("excess")=((2T)/(r_(1))) +((2T)/(r_(2)))`
`r_(1)=R and r_(2)=oo`
`P_("excess")=(2T)/(R)`