Surface Energy and Surface Tension (Angle of Contact, Excess of Pressure Across a Curved Surface, Application of Surface Tension - Drops, Bubbles, and Capillary Rise...) NEET Questions

Physics - Properties of Solids and Liquids

Surface Energy and Surface Tension (Angle of Contact, Excess of Pressure Across a Curved Surface, Application of Surface Tension - Drops, Bubbles, and Capillary Rise...) MCQ Questions


7.
The angle of contact θ is defined as:
A.
The angle at which light refracts at the liquid surface
B.
The angle between the tangent to the liquid surface at the point of contact and the solid surface, measured inside the liquid
C.
The contact angle between two immiscible liquids
D.
The angle between the liquid surface and the horizontal
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ANSWER :
B. The angle between the tangent to the liquid surface at the point of contact and the solid surface, measured inside the liquid
8.
At a liquid-solid interface, the angle of contact θ is obtuse (> 90°) when:
A.
The liquid wets the solid strongly (S_sl < S_la)
B.
The liquid is water and solid is glass
C.
S_sl > S_la — solid-liquid surface energy exceeds liquid-air surface energy; liquid does not wet solid
D.
The liquid molecules are strongly attracted to the solid surface
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ANSWER :
C. S_sl > S_la — solid-liquid surface energy exceeds liquid-air surface energy; liquid does not wet solid
9.
The equilibrium condition among the three surface tensions (S_la, S_sa, S_sl) at the contact line gives the relation:
A.
S_la cosθ = S_sa − S_sl
B.
S_la + S_sl = S_sa cosθ
C.
S_la sinθ = S_sa − S_sl
D.
S_la = S_sa = S_sl
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ANSWER :
A. S_la cosθ = S_sa − S_sl
10.
Soaps and detergents are called 'wetting agents.' When added to water, they:
A.
Decrease the surface tension and angle of contact, allowing water to spread and penetrate better
B.
Increase the angle of contact making water spread less
C.
Increase water density
D.
Increase the surface tension of water
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ANSWER :
A. Decrease the surface tension and angle of contact, allowing water to spread and penetrate better
11.
Excess pressure inside a spherical liquid DROP of radius r and surface tension S is:
A.
P_i − P_o = 2S/r
B.
P_i − P_o = S/r
C.
P_i − P_o = 4S/r
D.
P_i − P_o = S/(2r)
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ANSWER :
A. P_i − P_o = 2S/r
12.
Excess pressure inside a SOAP BUBBLE of radius r and surface tension S is:
A.
P_i − P_o = 4S/r
B.
P_i − P_o = S/r
C.
P_i − P_o = 2S/r
D.
P_i − P_o = 8S/r
😑 View Answer Rough Work Error
ANSWER :
A. P_i − P_o = 4S/r