64. The angle of contact in case of a liquid depends upon
A.The nature of the liquid and the solid
B.The material which exists above the free surface of the liquid
C.Both of the above
D.Any one of the above

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65. Free surface of a liquid behaves like a sheet and tends to contract to smallest possible area due to the
A.Force of adhesion
B.Force of cohesion
C.Force of friction
D.Force of diffusion

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66. Rain drops are spherical because of
A.Viscosity
B.Air resistance
C.Surface tension forces
D.Atmospheric pressure

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67. Surface energy per unit area of a surface is numerically equal to
A.Atmospheric pressure
B.Surface tension
C.Force of adhesion
D.Force of cohesion

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68. The capillary rise at 20?C in a clean glass tube of 1 mm bore containing water is approximately
A.1 mm
B.30 mm.
C.10 mm
D.20 nun

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69. If the surface of liquid is convex, then
A.Cohesion. pressure is negligible
B.Cohesion pressure is decreased
C.Cohesion pressure is increased
D.There is no cohesion pressure

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70. To avoid vaporisation in the pipe line, the pipe line over the ridge is laid such that it is not more than
A.2.4 m above the hydraulic gradient
B.6.4 m above the hydraulic gradient
C.10.0 m above the hydraulic gradient
D.5.0 above the hydraulic gradient

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