JEE Advanced 2020 Concept Recapitulation Test 2 Paper 1

The shape of water layer between the two plates is shown in the figure.
Thickness d of the film =0.12mm=0.012cm.
Radius R of cylindrical face =‌

d

2

.
F=T(21)=P(I×2R)
P=‌

T

R

Pressure difference across the cylindrical surface =‌

T

R

=‌

2T

d

.
Area of each plate wetted by water =A.
Force F required to separate the two plates is given by
F= pressure difference × area =‌

2T

d

A
=‌

2×75×8

0.012

=105 dynes