The radius of a soap bubble is increased from R to 2 R. Work done in this process (T = surface tension) is: 

A certain number of spherical drops of a liquid of radius r coalesce to form a single drop of radius R and volume V. If T is the surface tension of the liquid, then:\(\text { Energy }=4 V T\left(\frac{1}{r}-\frac{1}{R}\right) \text { is released } \)

At which of the following temperatures, the value of surface tension of water is minimum ?

(1) $4°\mathrm{C}$                                       

(2) $25°\mathrm{C}$

(3) $50°\mathrm{C}$                                     

(4) $75°\mathrm{C}$

If a glass rod is dipped in mercury and withdrawn out, the mercury does not wet the rod because 

(1) Angle of contact is acute

(2) Cohesion force is more

(3) Adhesion force is more

(4) The density of mercury is more

Mercury does not wet glass, wood or iron because

(1) Cohesive force is less than the adhesive force

(2) Cohesive force is greater than the adhesive force

(3) The angle of contact is less than 90^o

(4) Cohesive force is equal to the adhesive force

Surface tension of a liquid is found to be influenced by

(1) It increases with the increase of temperature

(2) Nature of the liquid in contact

(3) Presence of soap that increases it

(4) Its variation with the concentration of the liquid

When a drop of water is dropped on oil surface, then

(1) It will mix up with oil

(2) It spreads in the form of a film

(3) It will deform

(4) It remains spherical

Small liquid drops assume spherical shape because

(1) Atmospheric pressure exerts a force on a liquid drop

(2) Volume of a spherical drop is minimum

(3) Gravitational force acts upon the drop

(4) Liquid tends to have the minimum surface area due to surface tension

It is easy to wash clothes in hot water because its

(1) Surface tension is more

(2) Surface tension is less

(3) Consumes less soap

(4) None of these

The force required to separate two glass plates of area ${10}^{-2}{\mathrm{m}}^2$ with a film of water 0.05 mm thick between them, is (Surface tension of water is $70\times {10}^{-3 }$N/m)

(a) 28 N                         (b) 14 N
(c) 50 N                         (d) 38 N