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WBJEE 2014 Physics Solved Paper
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© examsnet.com
Question : 12
Total: 60
A drop of some liquid of volume 0.04
c
m
3
is placed on the surface of a glass slide. Then another glass slide isplaced on it in such a way that the liquid forms a thin layer of area 20
c
m
2
between the surfaces of the two slides. Toseparate the slides a force of 16 ×
10
5
dyne has to be applied normal to the surfaces. The surface tension of the liquidis (in
d
y
n
e
−
c
m
–
1
)
60
70
80
90
Validate
Solution:
Let thickness of layer is t
V = At, t =
V
A
, 2r =
V
A
, r =
V
2
A
, ΔP =
T
r
F = ΔP × A =
T
r
× A =
T
(
V
2
A
)
A , F =
2
T
A
2
V
= 80 dyne / cm
© examsnet.com
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