11dunno... only this much was asked and no figure was given...
A small drop of water of surface tension ∂ is squeezed between two clean glass plates so that a thin layer of thickness d and area a is formed between them. If the angle of contact is zero , the force required to pull the plates apart is :
a) ∂ Ad
b)2 ∂ Ad
c)4 ∂ Ad
d)8 ∂ Ad
the answer given is b
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10 Answers
11
1the interface fromed between the twoglass plates has two surfaces one facing each plate
so according to the definition of surface tension " the force acting per unit length"that is
T=F/L
so here the area is given as A and the thickness is given as d
so L=A/d
therefore according to the formula of surface tension
T=F/L
implies ∂=F/(A/d)
implies (∂*A)/d=F
but the point to note here is that the above force is the force which is acting at any one of the surface of the two glass plates inwards so
the total force acting on the both glass surfaces =2*F=2*∂A/d
so an equal amount of force has to be applied to pull the plates apart from the disccused state
thereforce the required pulling force to pull the plates apart=2*F=2∂A/d
hence the correct ans is option (b)2∂A/d
1I believe the question is this!!
And according to me ans should be 'C'
71You mean you don't agree with previous solution OR this might also be a solution?
1Yes I dont agree with the solution as when angle of contact is zero then force of surface tension acts parallel to the plates.