Title 10. Surface Tension Med.pdf ✅

1. A wooden stick 2m long is floating on the surface of water. The surface tension of water 0.07 N/m. By putting soap solution on one side of the sticks the surface tension is reduced to 0.06 N/m. The net force on the stick will be (a) 0.07 N (b) 0.06 N (c) 0.01 N (d) 0.02 N 2. A thin metal disc of radius r floats on water surface and bends the surface downwards along the perimeter making an angle  with vertical edge of disc. If the disc displaces a weight of water W and surface tension of water is T, then the weight of metal disc is (a) 2rT + W (b) 2rTcos – W (c) 2rTcos + W (d) W – 2rTcos 3. A 10 cm long wire is placed horizontally on the surface of water and is gently pulled up with a force of N 2 2 10 −  to keep the wire in equilibrium. The surface tension in Nm–1 of water is (a) 0.1 N/m (b) 0.2 N/m (c) 0.001 N/m (d) 0.002 N/m 4. There is a horizontal film of soap solution. On it a thread is placed in the form of a loop. The film is pierced inside the loop and the thread becomes a circular loop of radius R. If the surface tension of the loop be T, then what will be the tension in the thread (a) R / T 2  (b) R T 2  (c) 2RT (d) 2RT 5. A liquid is filled into a tube with semi-elliptical cross-section as shown in the figure. The ratio of the surface tension forces on the curved part and the plane part of the tube in vertical position will be (a) b a b 4 ( + ) (b) b 2a (c) b a 4  (d) b a b 4 ( − ) 6. A liquid film is formed over a frame ABCD as shown in figure. Wire CD can slide without friction. The mass to be hung from CD to keep it in equilibrium is (a) g Tl (b) g 2Tl (c) Tl g 2 (d) T  l 7. Radius of a soap bubble is increased from R to 2R work done in this process in terms of surface tension is (a) R S 2 24 (b) R S 2 48 (c) R S 2 12 (d) R S 2 36 8. Pressure inside two soap bubbles are 1.01 and 1.02 atmospheres. Ratio between their volumes is (a) 102 : 101 (b) 3 3 (102) : (101) (c) 8 : 1 (d) 2 : 1 9. The excess pressure inside an air bubble of radius r just below the surface of water is P1. The excess pressure inside a drop of the same radius just outside the surface is P2. If T is surface tension then (a) P1 = 2P2 (b) P1 = P2 (c) P2 = 2P1 (d) P2 = 0, P1  0 10. Water rises to a height of 10cm in a capillary tube and mercury falls to a depth of 3.5cm in the same capillary tube. If the density of mercury is 13.6 gm/cc and its angle of contact is 135o and density of water is 1 gm/cc and its angle of contact is o 0 , then the ratio of surface tensions of the two liquids is (cos135 = 0.7) o (a) 1 : 14 (b) 5 : 34 (c) 1 : 5 (d) 5 : 27 11. Water rises in a vertical capillary tube upto a height of 2.0 cm. If the tube is inclined at an angle of o 60 with the vertical, then upto what length the water will rise in the tube (a) 2.0 cm (b) 4.0 cm (c) 3 4 cm (d) 2 2 cm 12. Two capillary tubes of same diameter are kept vertically one each in two liquids whose relative densities are 0.8 and 0.6 and surface tensions are 60 and 50 dyne/cm respectively. Ratio of heights of liquids in the two tubes 2 1 h h is (a) 9 10 (b) 10 3 (c) 3 10 (d) 10 9 13. A capillary tube of radius R is immersed in water and water rises in it to a height H. Mass of water in the capillary tube is M. If the radius of the tube is doubled, mass of water that will rise in the capillary tube will now be (a) M (b) 2M (c) M/2 (d) 4M 14. Water rises to a height h in a capillary at the surface of earth. On the surface of the moon the height of water column in the same capillary will be (a) 6h (b) h 6 1 (c) h (d) Zero 15. Water risesupto a height h in a capillary on the surface of earth in stationary condition. Value of h increases if this tube is taken (a) On sun (b) On poles (c) In a lift going upward with acceleration (d) In a lift going downward with acceleration l D C A B Liquid film b a
16. If the surface tension of water is 0.06 N/m, then the capillary rise in a tube of diameter 1mm is ( 0 ) o  = (a) 1.22 cm (b) 2.44 cm (c) 3.12 cm (d) 3.86 cm 17. Two capillaries made of same material but of different radii are dipped in a liquid. The rise of liquid in one capillary is 2.2cm and that in the other is 6.6cm. The ratio of their radii is (a) 9 : 1 (b) 1 : 9 (c) 3 : 1 (d) 1 : 3 18. The lower end of a capillary tube is at a depth of 12cm and the water rises 3cm in it. The mouth pressure required to blow an air bubble at the lower end will be X cm of water column where X is (a) 3 (b) 9 (c) 12 (d) 15 19. The lower end of a capillary tube of radius r is placed vertically in water. Then with the rise of water in the capillary, heat evolved is (a) dg J r h 2 2 2  + (b) J r h dg 2 2 2  + (c) J r h dg 2 2 2  − (d) J r h dg 2 2  − 20. Water rises in a capillary tube to a certain height such that the upward force due to surface tension is balanced by N 4 75 10 −  force due to the weight of the liquid. If the surface tension of water is 6 10 N /m −2  , the inner circumference of the capillary must be (a) m 2 1.25 10 −  (b) m 2 0.50 10 −  (c) m 2 6.5 10 −  (d) m 2 12.5 10 −  21. The radii of two soap bubbles are r1 and r2. In isothermal conditions, two meet together in vacuum. Then the radius of the resultant bubble is given by (a) ( ) / 2 1 2 R = r + r (b) ( ) 1 1 2 2 R = r r r + r (c) 2 2 2 1 2 R = r + r (d) 1 2 R = r + r 22. Two soap bubbles of radii r1 and r2 equal to 4cm and 5cm are touching each other over a common surface 1 2 S S (shown in figure). Its radius will be (a) 4 cm (b) 20 cm (c) 5 cm (d) 4.5 cm 23. On dipping one end of a capillary in liquid and inclining the capillary at an angles o 30 and o 60 with the vertical, the lengths of liquid columns in it are found to be 1 l and 2 l respectively. The ratio of 1 l and 2 l is (a) 1 : 3 (b) 1 : 2 (c) 2 : 1 (d) 3 : 1 24. A drop of water of volume V is pressed between the two glass plates so as to spread to an area A. If T is the surface tension, the normal force required to separate the glass plates is (a) V TA2 (b) V TA2 2 (c) V TA2 4 (d) V TA 2 2 25. If a liquid does not wet glass, its angle of contact is: (a) Zero (b) Acute (c) Obtuse (d) Right angle 26. When a loaded boat enters into the sea from a river, it rises because: (a) There is more water in the sea than in river (b) Sea water is denser than river (c )There is difference of temperature (d) Sea is deeper than river 27. Two rain drops reach the earth with the terminal velocities in the ratio 4 : 9. The ratio of radii is : (a) 4 : 9 (b) 2 : 3 (c) 3 : 2 (d) 9 : 4 28. If two soap bubbles of different radii are connected by a tube, (a) Air flows from the bigger bubble to the smaller bubble till the sizes become equal (b) Air flows from bigger bubble to the smaller bubble till the sizes air interchanged (c) Air flows from the smaller bubble to the bigger (d) There is no flow of air 29. The surface tension of a liquid is 5 N/m. If a film is held on a ring of area 0.02 m2 , its total surface energy is about - (a) 5 × 10–2 J (b) 2.5 × 10–2 J (c) 2 × 10–1 J (d) 3 × 10–1 J 30. A very narrow capillary tube records a rise of 20 cm when dipped in water. When the area of cross section is reduced to one fourth of the former value, water will rise to a height of- (a) 10 cm (b) 20 cm (c) 40 cm (d) 80 cm 31. Water rises to a height of 16.3 cm in a capillary of height 18 cm. If the tube is cut at a height of 12 cm , then- (a) Water will come as a fountain from the capillary (b) Water will stay at a height of 12 cm in capillary (c) The height of the water in the tube will be 10.3 cm (d) Water will flow down the sides of the capillary tube 32. When detergent is added to water, surface tension of solution (a) Remain same as that of detergent (b) Is reduced (c) Increased (d) May decrease or increase depending upon type of detergent 33. With rise in temperature- (a) Surface tension increases (b) Surface tension decreases 4 cm 5 cm S1 S2
(c) Surface tension may become zero if temperature reaches the critical value (d) (b) and (c) both 34. Which water is having detergent dissolved in it P Q (a) P (b) Q (c) Both (d) Data insufficient 35. In a capillary tube, water rises to a height of 4 cm. If the cross- sectional area of the tube were one-fourth, water would have risen to a height of- (a) 2 cm (b) 4 cm (c) 8 cm (d) 16 cm 36. A mercury pallet is trapped between two horizontal glass plate having small space between them. The shape of mercury pallet is best described by- (a) (b) (c) (d) 37. The pressure inside two soap bubbles are 1.02 atm. and 1.03 atm. respectively. The ratio of their volumes is - (a) 102 : 103 (b) 103 : 102 (c) (103)3 : (102)3 (d) 27 : 8 38. A capillary tube (P) is dipped in water. Another identical tube (Q) is dipped in a soap water solution. Which of the following shows the relative nature of the liquids columns in the two tubes? (a) P Q (b) P Q (c) P Q (d) P Q 39. A metallic wire of density  floats horizontal in water. The maximum radius of the wire sothat the wire may not sink will be : (surface tension of water = T and angle of contact  = 00 ) - (a) g 2T  (b) g 4T  (c) g T  (d) g T   40. In the bottom of a vessel with mercury of density  there is a round hole of radius r. At what maximum height of the mercury layer will the liquid still not flow out through this hole? (Surface tension = T) - (a) r g T  (b) 2r g T  (c) r g 2T  (d) r g 4T  41. In a U-tube the radii of two columns are respectively r1 and r2. When a liquid of density  ( = 0o) is filled in it, a level difference of h is observed on two arms, then the surface tension of the liquid is - (a) ( – ) 2 1 1 2 2 r r ghr r (b) hg (r2– r1) (c) 2 h g r r 2 1  ( – ) (d) ( – ) 2 1 2 r r hg 42. A coaxial cylinder made of glass is immersed in liquid of surface tension ‘S’. Radius of inner and outer surface of cylinder are R1 and R2 respectively. Height till which liquid will rise is (Density of liquid is )- (a) R g 2S 2 (b) R g 2S 1 (c) (R R ) g S 2 − 1  (d) (R R ) g 2S 2 − 1  43. A conical pipe shown in figure have a water drop. The drop will tend to move towards- (a) Tapered end (b) Wider end (c) In any direction (d) No tendency to move 44. Graph between the mass of liquid inside the capillary and radius of capillary is – (a) r m (b) r m (c) r m (d) r m 45. If one increases the volume of a soap bubble the surface tension of the bubble- (a) Increase (b) Decrease (c) Remains the same (d) Becomes zero
46. A water drop is divided into eight equal droplets the pressure difference between the inner and outer side of the big drop will be - (a) Same as for smaller droplet (b) 1/2 of that for smaller droplet (c) 1/4 of that for smaller droplet (d) Twice that for smaller droplet 47. The work done to get 'n' smaller equal size spherical drops from a bigger size spherical drop of water is proportional to - (a) 2/3 n 1 –1 (b) 1/3 n 1 –1 (c) n1/3 –1 (d) n4/3 – 1 48. In a capillary tube experiment, a vertical 30 cm long capillary tube is dipped in water. The water rises up to a height of 10 cm due to capillary action. If water temperature increases then new height of water column in capillary becomes– (a) 30 cm (b) Greater than 10 cm (c) Equal to 10 cm (d) Less than 10 cm 49. A mosquito with 8 legs stands on water surface and each leg makes depression of radius 'a'. If the surface tension and angle of contact are 'T' and zero respectively then the weight of mosquito is- (a) 8T.a (b) 16  Ta (c) 8 Ta (d) 16 Ta 50. A very narrow capillary tube records a rise of 20 cm when dipped in water. When the area of cross-section is reduced to one-fourth of former value, water will rise to a height of - (a) 10 cm (b) 20 cm (c) 40 cm (d) 80 cm 51. Find the excess pressure on one side of a soap film of surface tension T over that on the other side r1 and r2 are radii of two surfaces – r1 r2 P3 P2 P1 (a) 2 T       1 2 r 1 – r 1 (b) 2T         + 1 2 r 1 r 1 (c) T       1 2 r 1 – r 1 (d) T       + 1 2 r 1 r 1 52. A 10 cm long wire is brought 20 cm up in a liquid of surface tension 40 dyne cm–1 . Find the work done against surface tension- (a) 0.8 m J (b) 1.6 m J (c) 1.2 m J (d) 3.2 m J 53. Neglecting gravity, the potential energy of a molecule of liquid on the surface of liquid as compared to a molecule inside liquid is : (a) greater (b) less (c) equal (d) depending on the liquid sometimes more, sometimes less 54. A thread is tied slightly loose to a wire frame as shown in the figure. And the frame is dipped into a soap solution and taken out. The frame is completely covered with the film. When the portion A is punctured with a pin, then the thread : (a) becomes convex towards A (b) becomes concave towards A (c) remains in the initial position (d) either (a) or (b) depending on size of A w.r.t. B 55. In a surface tension experiment with a capillary tube, water rises upto 0.1 m. If the same experiment is repeated in an artificial satellite, which is revolving around the earth ; water will rise in the capillary tube upto a height of : (a) 0.1 m (b) 0.2 m (c) 0.98 m (d) full length of tube 56. The surface tension of a liquid is 5 N/m. If a film is held on a ring of area 0.02 m2 , its surface energy is about : (a) 5 × 10–2 J (b) 2.5 × 10–2 J (c) 2 × 10–1 J (d) 3 × 10–1 J