Surface Tension & Capillarity — Practice Questions

Free NEET Physics multiple-choice questions on Surface Tension & Capillarity. Attempt each question and reveal the answer with a full explanation.

Which of the following properties of water is used in the determination of its surface tension by the capillary rise method? Cohesion and Adhesion Viscosity Density only Compressibility Which of the following properties of a liquid is responsible for the spherical shape of rain drops? Surface tension Viscosity Density Atmospheric pressure Water is used as a coolant in automobile radiators because of its: High specific heat capacity Low density High thermal conductivity Low boiling point The angle of contact for a liquid which does not wet the glass surface (like mercury) is: Obtuse ( >90 ) Acute ( <90 ) Zero Right angle The excess pressure inside an air bubble of radius R inside a liquid of surface tension T is: 2T/R 4T/R T/R 8T/R The addition of soap or detergent to water: Decreases the surface tension Increases the surface tension Does not change the surface tension Makes the angle of contact obtuse As the temperature of a liquid increases, its surface tension generally: Decreases Increases Remains constant First increases then decreases A spherical drop of water has a radius of 2 mm . If the surface tension of water is 70 10 -3 N/m , the excess pressure inside the drop is: 70 Pa 35 Pa 140 Pa 280 Pa The excess pressure inside a cylindrical liquid jet of radius R and surface tension T is: T/R 2T/R 4T/R T/2R The energy required to blow a soap bubble of radius R is W 1 and that for a bubble of radius 2R is W 2 . The ratio W 2/W 1 is: 4 8 2 2 If the ratio of the diameter of two capillaries is 1:2 , the ratio of the heights to which water will rise in them is: 2:1 1:2 4:1 1:4 When the temperature of a liquid is increased, its surface tension usually: Decreases Increases Remains constant First increases then decreases The temperature of inversion of a thermocouple is 620 C and the neutral temperature is 300 C . What is the temperature of cold junction : 40 C 20 C 320 C -20 C Which of the following circular rods, (given radius r and length ) each made of the same material and whose ends are maintained at the same temperature will conduct most heat r=2r 0; =2 0 r=2r 0; = 0 r=r 0; =2 0 r=r 0; = 0 A black body is at 727° C. It emits energy at a rate which is proportional to (1000) 4 (1000) 2 (727) 4 (727) 2 The two ends of a rod of length L and a uniform cross-sectional area A are kept at two temperatures T 1 and T 2 (T 1>T 2) . The rate of heat transfer, dQ dt , through the rod in a steady state is given by : dQ dt = kA(T 1-T 2) L dQ dt = kL(T 1-T 2) A dQ dt = k(T 1-T 2) LA dQ dt =kLA(T 1-T 2) Steam at 100 C is passed into 20 g of water at 10 C . When water acquires a temperature of 80 C , the mass of water present will be : [Take specific heat of water = 1 cal g -1 C -1 and latent heat of steam = 540 cal g -1 ] 24 g 31.5 g 42.5 g 22.5 g Coefficient of linear expansion of brass and steel rods are 1 and 2 . Lengths of brass and steel rods are 1 and 2 respectively. If ( 2 - 1) is maintained same at all temperatures, which one of the following relations holds good ? 1 2 = 2 1 1 2 2 = 2 1 2 1 2 = 2 2 1 1 1 = 2 2 The unit of thermal conductivity is : W m -1 K -1 J m K -1 J m -1 K -1 W m K -1 A copper rod of 88 cm and an aluminium rod of unknown length have their increase in length independent of increase in temperature. The length of aluminium rod is : ( Cu =1.7 10 -5 K -1 and Al =2.2 10 -5 K -1 ) 68 cm 6.8 cm 113.9 cm 88 cm The quantities of heat required to raise the temperature of two solid copper spheres of radii r 1 and r 2 ( r 1 = 1.5 r 2 ) through 1 K are in the ratio : 9 4 3 2 5 3 27 8 A capillary tube of radius r is immersed in water and water rises in it to a height h . The mass of the water in the capillary is 5 g . Another capillary tube of radius 2r is immersed in water. The mass of water that will rise in this tube is: 10 g 5 g 20 g 2.5 g A capillary tube of radius r is immersed in a liquid of density and surface tension T . If the angle of contact is , the vertical component of the surface tension force supporting the liquid column is: 2 r T r 2 T 2 r T T 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: 0.125 N/m 0.250 N/m 0.5 N/m 8 N/m Three liquids of densities 1, 2, 3 (with 1 > 2 > 3 ), having the same value of surface tension T , rise to the same height h in three identical capillaries. The angles of contact 1, 2, 3 obey: 2 > 1 > 2 > 3 0 1 > 2 > 3 > 2 1 < 2 < 3 0 1 < 2 < 3 < 2 Water rises to a height h in a capillary tube. If the length of capillary tube above the surface of water is made less than h , then: Water rises up to the top of capillary tube and stays there without overflowing Water rises up to the tip and then starts overflowing like a fountain Water rises up to a point and stays there Water does not rise at all Two soap bubbles of radii a and b ( b > a ) combine to form a single bubble of radius c under isothermal conditions in vacuum. The relation between the radii is: c 2 = a 2 + b 2 c = a + b c 3 = a 3 + b 3 c 2 = b 2 - a 2 A capillary tube is dipped in water and the water rises to a height h . If the entire apparatus is allowed to fall freely under gravity, the height of the water column in the capillary will be: The full length of the tube h Zero 2h The work done in blowing a soap bubble from a radius of 3 cm to 5 cm is (Surface tension of soap solution T = 3 10 -2 N/m ): 1.21 10 -3 J 6.03 10 -4 J 3.01 10 -4 J 2.42 10 -3 J A ring of radius r is made of a thin wire of mass m . It is floating on the surface of water of surface tension T . The minimum force required to lift the ring from the water surface is: mg + 4 r T mg + 2 r T mg + 8 r T 2 r T The excess pressure inside a soap bubble is twice the excess pressure inside a second soap bubble. The volume of the first bubble is n times the volume of the second bubble. The value of n is: 0.125 0.25 2 8 In a capillary tube of radius r , water rises to a height h . The tube is then inclined at an angle of 60 with the vertical. The length of the water column in the tube will be: 2h h h/2 1.5h A needle of length l and density floats on the surface of a liquid of surface tension T . The maximum weight of the needle that can be supported by surface tension is: 2Tl Tl Tl/2 4Tl At what temperature will the surface tension of water be zero? Critical temperature 100 C 0 C 273 C Two soap bubbles of radii r 1 and r 2 are connected by a tube. Air will flow from: The smaller bubble to the larger bubble The larger bubble to the smaller bubble Neither, as both have same pressure Depends on the length of the tube Which of the following physical quantities has the same dimensions as Surface Tension? Spring constant Stress Strain Surface energy Water rises in a capillary tube to a height h . If the tube is taken to the moon, where the acceleration due to gravity is 1/6 th that of the earth, the height of the water column will be: 6h h/6 h 36h The pressure inside a soap bubble of radius R 1 is P 1 and that inside another soap bubble of radius R 2 is P 2 . If the pressure outside is P 0 , then the pressure difference P 1 - P 2 is: 4T ( 1 R 1 - 1 R 2 ) 2T ( 1 R 1 - 1 R 2 ) 4T ( 1 R 2 - 1 R 1 ) T ( 1 R 1 - 1 R 2 ) The work done in increasing the radius of a soap bubble from R to 2R is W . The work done in increasing the radius from 2R to 3R is: 5 3 W W 2W 4 3 W The excess pressure inside a spherical drop of water is 20 N/m 2 . If eight such drops coalesce into a single larger drop, the excess pressure inside the larger drop will be: 10 N/m 2 40 N/m 2 5 N/m 2 20 N/m 2 A thin liquid film is formed between a U-shaped wire and a light slider of length 30 cm (see figure). The slider is supported by a weight of 1.5 10 -2 N . The surface tension of the liquid is: 0.025 N/m 0.05 N/m 0.1 N/m 0.0125 N/m When a capillary tube of insufficient length is dipped in water, the water: Rises to the top and stays there without overflowing Overflows like a fountain Does not rise at all Rises and then falls back The work done in blowing a soap bubble from radius R to 3R is W . What is the work done in blowing it from 3R to 5R ? 2W 3W 4W 1.5W A square frame of side L is dipped in a liquid of surface tension T . The force required to pull the frame out of the liquid is: 8LT + mg 4LT + mg 2LT + mg LT + mg The wettability of a surface by a liquid depends primarily on: Angle of contact between the surface and the liquid Viscosity Surface tension Density A capillary tube of radius r is immersed in water and water rises to a height h . If the tube is pushed further into the water such that only length h/2 is above the water surface, then: The water will reach the top and its meniscus will become less curved Water will overflow like a fountain Water will not rise at all Water will rise to height h/2 and then stop A thousand small water drops of equal radii coalesce to form one big drop. The ratio of the total surface energy of a thousand drops to that of a single big drop is: 10 : 1 100 : 1 1 : 10 1 : 100 Water rises to a height h in a vertical capillary tube. If the tube is tilted at an angle with the vertical, the length of the water column along the tube will be: h/ h h/ h An air bubble of radius r is formed inside another air bubble of radius R ( R > r ) in a soap solution of surface tension T . The excess pressure inside the smaller bubble relative to outside the larger bubble is: 4T(1/r + 1/R) 4T/r 4T/R 2T(1/r + 1/R) An air bubble of radius r in water is at a depth h below the water surface. The total pressure inside the bubble is: ( P 0 = atmospheric pressure, = density of water, T = surface tension ) P 0 + gh + 2T/r P 0 + gh + 4T/r P 0 + gh gh + 2T/r What is the pressure inside a drop of mercury of radius 3.0 mm at room temperature? Surface tension of mercury at 20 C is 4.65 10 -1 N/m . The atmospheric pressure is 1.01 10 5 Pa . 1.013 10 5 Pa 3.10 10 2 Pa 1.01 10 5 Pa 1.02 10 5 Pa A liquid rises in a capillary tube to a height H when the tube is vertical. If the tube is tilted at an angle 60 with the vertical, the length of the liquid column in the tube will be: 2H H/2 3 H/2 H A spherical drop of liquid of radius R is divided into 8 equal droplets. If T is the surface tension of the liquid, the work done in this process is: 4 R 2 T 8 R 2 T 2 R 2 T R 2 T An air bubble of radius r is at a depth h below the surface of a liquid of density and surface tension T . If P 0 is the atmospheric pressure, the pressure inside the bubble is: P 0 + gh + 2T/r P 0 + gh + 4T/r P 0 + 2T/r P 0 + gh A small drop of water of surface tension T and radius r is broken into n smaller droplets of equal size. The change in surface energy is: 4 r 2 T (n 1/3 - 1) 4 r 2 T (n 2/3 - 1) 4 r 2 T (n - 1) 4 r 2 T (n 1/2 - 1) The excess pressure inside a soap bubble of radius R is P 1 and that inside a water drop of the same radius is P 2 . The relation between P 1 and P 2 is: P 1 = 2P 2 P 1 = P 2 P 2 = 2P 1 P 1 = 4P 2 A black body at 1227 C emits radiations with maximum intensity at a wavelength of 5000 . The temperature of the body is increased by 1000 C , the maximum intensity will be observe at:- 4000 5000 6000 3000 A black body at 227 C radiates heat at the rate of 7 cals/cm 2 s. At a temperature of 727 C , the rate of heat radiated in the same units will be : 80 60 50 112 A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using Stefan's Law Wien's displacement Law Kirchoff's Law Newton's Law of cooling Certain quantity of water cools from 70 C to 60 C in the first 5 minutes and to 54 C in the next 5 minutes. The temperature of the surroundings is:- 45 C 20 C 42 C 10 C In a certain planetary system, it is observed that one of the celestial bodies having a surface temperature of 200K, emits radiation of maximum intensity near the wavelength 12 m. The surface temperature of a nearby star which emits light of maximum intensity at a wavelength = 4800 , is : 7500 K 5000 K 2500 K 10000 K A wall consists of alternating blocks of length ‘d’ and coefficient of thermal conductivity K 1 and K 2 respectively as shown in figure. The cross sectional area of the blocks are the same. The equivalent coefficient of thermal conductivity of the wall between left and right is : K 1+K 2 2 2K 1K 2 K 1+K 2 K 1+K 2 3 3K 1K 2 K 1+K 2 The power radiated by a black body is P and it radiates maximum energy at wavelength, 0 . If the temperature of the black body is now changed so that it radiates maximum energy at wavelength 3 4 0 , the power radiated by it becomes nP. The value of n is 256 81 4 3 3 4 81 256 A cup of coffee cools from 90 C to 80 C in t minutes, when the room temperature is 20 C . The time taken by a similar cup of coffee to cool from 80 C to 60 C at a room temperature same at 20 C is 13 5 t 10 13 t 5 13 t 13 10 t Three identical heat conducting rods are connected in series as shown in the figure. The rods on the sides have thermal conductivity 2K while that in the middle has thermal conductivity K . The left end of the combination is maintained at temperature 3T and the right end at T . The rods are thermally insulated from outside. In steady state, temperature at the left junction is T 1 and that at the right junction is T 2 . The ratio T 1/T 2 is 5 4 3 2 4 3 5 3 A soap bubble, having radius of 1 mm , is blown from a detergent solution having a surface tension of 2.5 10 -2 N/m . The pressure inside the bubble equals at a point Z 0 below the free surface of water in a container. Taking g = 10 m/s 2 , density of water = 10 3 kg/m 3 , the value of Z 0 is: 1 cm 0.5 cm 10 cm 2 cm The shape of the meniscus of water in a glass capillary is concave whereas that of mercury is convex. This is because: Adhesive force between water and glass > Cohesive force between water molecules Cohesive force between water molecules > Adhesive force between water and glass Surface tension of water is high Density of mercury is high 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: Energy = 3VT( 1 r - 1 R ) is released Energy is neither released nor absorbed Energy = 4VT( 1 r - 1 R ) is released Energy = 3VT( 1 r + 1 R ) is absorbed An air bubble of radius 1 cm rises from the bottom of a lake to its surface. If the depth of the lake is 11 m and the atmospheric pressure is 10 5 Pa , what is the radius of the bubble when it reaches the surface? (Take g = 10 m/s 2 , density of water = 10 3 kg/m 3 and assume isothermal process) ∛ 2.1 cm 2.1 cm ∛ 1.1 cm 1.1 cm N identical water drops, each of radius r and surface tension T , coalesce to form a single big drop of radius R . If the energy released is converted into kinetic energy, the velocity of the big drop is (where is density): 6T ( 1 r - 1 R ) 3T ( 1 r - 1 R ) 12T ( 1 r - 1 R ) T ( 1 r - 1 R ) A flat glass plate is placed over another glass plate with a thin film of water of thickness d between them. If A is the area of the film and T is the surface tension of water, the force required to separate the plates is: 2AT d AT d AT 2d 4AT d Water rises to a height of 10 cm in a capillary tube and mercury falls to a depth of 3.5 cm in the same capillary tube. If the density of mercury is 13.6 g/cm 3 and its angle of contact is 135 and that of water is 0 , then the ratio of surface tensions of mercury and water is: 7.2 6.5 5.4 8.1 A spherical drop of liquid with radius R is broken into n droplets of equal radius r . The work done in the process is ( T is surface tension): 4 R 2 T(n 1/3 - 1) 4 R 2 T(n 2/3 - 1) 4 R 2 T(n - 1) 4 R 2 T(n 1/2 - 1) Two soap bubbles have radii in the ratio 2:3 . The ratio of excess pressure inside them is: 3:2 2:3 4:9 9:4 A liquid does not wet the solid surface if the angle of contact is: Greater than 90 ∘ Zero Less than 90 ∘ Equal to 45 ∘