EASY
Earn 100

Why does soap film have two surfaces?

Important Questions on Mechanical Properties of Fluids

MEDIUM
A thin metal wire of density ρ floats on water surface horizontally. If it is NOT to sink in water then maximum radius of wire is proportional to ( T= surface tension of water, g= gravitational acceleration)
MEDIUM
A liquid does not wet the solid surface if angle of contact is:
EASY
A wire of length 10 cm is gently placed horizontally on the surface of water having a surface tension of 75×10-3 N m-1. What force is required to just pull up the wire from the water surface?
EASY
Water does not wet an oily glass because
MEDIUM
The following observations were taken for determining surface tension T of water by capillary method:

diameter of capillary, D=1.25×10-2 m

rise of water, h=1.45×10-2 m

Using g=9.80 m s-2 and the simplified relation T=rhg2×103 N m-1 the possible error in surface tension is closest to:
MEDIUM
Two glass plates are separated by water and the distance between the plates is 0.10 mm. If the surface tension of water is 75 dynes per cm and area of each plate wetted by water is 8 cm2, the force applied to separate the two plates is,
MEDIUM
If a drop of liquid breaks into smaller droplets, it results in lowering of temperature of the droplets. Let a drop of radius R, break into N small droplets each of radius r, then decrease (drop) in temperature Q (given, specific heat of liquid drop=S and surface tension =T )
MEDIUM
A metal sheet 4 m on a side and of negligible thickness is attached to a balance and inserted into container fluid. The balance to which metal sheet is attached reads 0.50 N and the contact angle is found to be zero. A small amount of oil is then spread over the metal sheet. The contact angle now becomes 180° and the balance now reads 0.49 N. The surface tension of the fluid is
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EASY
When one end of the capillary is dipped in water, the height of the water column is h. The upward force of 105 dyne due to surface tension is balanced by the force due to the weight of the water column. The inner circumference of the capillary is
(Surface tension of water =7×10-2 N m-1)
EASY
Which one of the following statement is correct?
EASY
The radius R of the soap bubble is doubled under isothermal condition. If T be the surface tension of the soap bubble, the work done in doing so is given by
MEDIUM
Consider a bowl filled with water on which some black paper powder has been sprinkled uniformly. Now a drop of liquid soap is added at the center of the surface of the water. The picture of the surface immediately after this will look like
EASY
What causes the free surface of a liquid to have minimum area?
MEDIUM
Work done in increasing the size of a soap bubble from a radius of 3 cm to 5 cm is nearly (surface tension of soap solution =0.05Nm-1)
EASY
A cylindrical wire of length 1, density d is kept on the surface of the liquid. What can be the maximum radius, r of the wire such that it is in equilibrium due to the surface tension, T of liquid? (Assume 1>r and the contact angle is 0°, g is the acceleration due to gravity)
HARD

When water is filled carefully in a glass, one can fill it to a height h above the rim of the glass due to the surface tension of water. To calculate h just before water starts flowing, model the shape of the water above the rim as a disc of thickness h having semicircular edges, as shown schematically in the figure. When the pressure of water at the bottom of this disc exceeds what can be withstood due to the surface tension, the water surface breaks near the rim and water starts flowing from there. If the density of water, its surface tension and the acceleration due to gravity are 103 kg m-3,0.07 N m-1 and 10 m s-2 respectively, the value of h (in mm) is ________.

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EASY

When a long glass capillary tube of radius 0.015 cm is dipped in a liquid, the liquid rises to a height of 15 cm within it. If the contact angle between the liquid and glass is close to 0°, the surface tension of the liquid, is n Millinewton m-1. Write the value of 100n.

ρ(liquid) =900 kg m-3, g=10 m s-2

MEDIUM
A small spherical droplet of density d is floating exactly half immersed in a liquid of density ρ and surface tension T. The radius of the droplet is (take note that the surface tension applies an upward force on the droplet):
EASY
A rectangular film of liquid is extended from (4 cm×2 cm) to (5 cm×4 cm). If the work done is 3×10-4 J, the value of the surface tension of the liquid is
HARD
Assume that a drop of a liquid evaporates by a decrease in its surface energy so that its temperature remains unchanged. The minimum radius of the drop for this to be possible is. (The surface tension is T, the density of the liquid is ρ and L is its latent heat of vaporisation.)