1. The spherical form of a raindrop is due to –
(a) Density of liquid
(b) Surface tension
(c) Atmospheric pressure
(d) Gravitational force
[Chhattisgarh P.C.S. (Pre) 2003, 39th B.P.S.C. (Pre) 1994, Uttarakhand P.C.S. (Mains) 2002]
Ans. (b) Surface tension
- The surface tension of a raindrop forces it into a sphere because this shape has the smallest amount of surface area for the same amount of water.
- This is why raindrops are round.
|
2. A drop of water is spherical in shape. This is due to :
(a) Surface tension
(b) Low temperature
(c) Air resistance
(d) Viscosity of water
[Uttarakhand Lower Sub. (Pre) 2010]
Ans. (a) Surface tension
- A drop of water is round because of surface tension.
- This is because the molecules of the liquid stick together and pull the surface area inwards, making it as small as possible.
|
3. The raindrops are spherical because –
(a) They fall from a high height
(b) The air has resistance
(c) The water has surface tension
(d) None of the above
[U.P.P.C.S. (Pre) 2005]
Ans. (c) The water has surface tension
- Raindrops are round due to surface tension.
- This is because the molecules of water stick together because of the weak connections, known as hydrogen bonds, between them.
|
4. The tendency of a liquid drop to contract and occupy a minimum area is due to :
(a) Surface tension
(b) Viscosity
(c) Density
(d) Vapour pressure
[I.A.S. (Pre) 1997]
Ans. (a) Surface tension
- The surface of liquid droplets is usually as small as possible because of surface tension.
|
5. Oil spreads on the water surface because –
(a) Oil is denser than water
(b) Oil is less dense than water
(c) The surface tension of oil is more than water
(d) The surface tension of oil is less than water
[U.P.P.S.C. (GIC) 2010, U.P.P.C.S. (Pre) 1994]
Ans. (d) Surface tension of oil is less than water
- Oil spreads on water because its surface tension is lower than that of water.
- When oil is poured over water, the strong surface tension of water pulls the oil in all directions, making it spread on top of the water.
|
6. Kerosene oil floats on water because –
(a) Its density is greater than the density of water.
(b) Its density is less than the density of water.
(c) Its density is equal to that of the density of water.
(d) None of the above
[Uttarakhand Lower Sub. (Pre) 2010]
Ans. (b) Its density is less than the density of water.
- Kerosene oil is able to stay on top of water because it is not as heavy as the water.
|
7. Pressure inside a soap bubble is –
(a) More than atmospheric pressure
(b) Less than atmospheric pressure
(c) Equal to atmospheric pressure
(d) Half of atmospheric pressure
[U.P.P.C.S. (Pre) 2014, U.P.P.C.S. (Pre) 1995]
Ans. (a) More than atmospheric pressure
- Soap bubbles tend to be bigger because when soap is mixed with water, it lowers the tension on the surface of the bubble.
- The pressure inside the bubble is stronger than the pressure outside.
|
8. If two bubbles of soap of different diameters come in contact with a tube, then what will happen?
(a) The size of both bubbles will remain the same
(b) The smaller bubble will become smaller and bigger will become bigger
(c) The smaller bubble will become larger and larger will become smaller to get the same size
(d) Both bubbles will burst as soon as they come in contact
[R.A.S./R.T.S.(Pre) 2007]
Ans. (b) The smaller bubble will become smaller and bigger will become bigger
- When two soap bubbles are connected, the air will flow from the smaller bubble to the bigger one because the smaller bubble has higher pressure.
- This means the bigger bubble will get bigger as the smaller one gets smaller.
|
9. A hydrogen-inflated polyethylene balloon is released from the surface of the earth. As the balloon rises to an altitude up in the atmosphere, it will –
(a) Decrease in size
(b) Flatten into a disc-like shape
(c) Increase in size
(d) Maintain the same size and shape
[I.A.S. (Pre) 2003]
Ans. (c) Increase in size
- If you let go of a helium-filled polyethylene balloon from the ground, the air pressure will be lower the higher it goes up.
- The balloon will keep getting bigger until the pressure inside it is the same as the outside pressure.
|
10. What happens when some charge is placed on a soap bubble?
(a) Its radius increases
(b) Its radius decreases
(c) The bubble collapses
(d) None of the above
[U.P.P.C.S. (Pre) 2019]
Ans. (a) Its radius increases
- When a bubble is given either a positive or negative charge, it will get bigger because the charge will spread out over its surface.
- As the same charges push away from each other, the bubble will expand until the surface tension brings it back to balance.
|
11. Four wires of the same material and dimensions as mentioned below are stretched by a load of the same magnitude separately. Which one of them will be elongated maximum?
(a) Wire of 1 m length and 2 mm diameter
(b) Wire of 2 m length and 2 mm diameter
(c) Wire of 3m length and 1.5 mm diameter
(d) Wire of 1m length and 1 mm diameter
[I.A.S. (Pre) 2007]
Ans. (c) Wire of 3m length and 1.5 mm diameter
- R The four wires are all made out of the same material, so they all have the same amount of Young modulus (elasticity).
- Y = f / A/∆l/L = f L/A∆l = f L/π r²∆ L
∆ Lα r L/r²
- The longer the wire, the more it will stretch, and the thicker the wire, the less it will stretch.
- Therefore, option (c) will have the most stretching.
|
12. Consider the following statement. If there were no phenomenon of capillarity, then
1. It would be difficult to use a kerosene lamp
2. One would not be able to use a straw to consume a soft drink.
3. The blotting paper would fail to function.
4. The big trees that we see around us would not have grown on the earth.
Which of the following statements given above are correct?
(a) 1, 2, and 3 only
(b) 1, 3, and 4 only
(c) 2 and 4 only
(d) 1, 2, 3 and 4 only
[I.A.S. (Pre) 2012]
Ans. (b) 1, 3, and 4 only
- Capillary action is the ability of liquids to move through small spaces without the help of gravity or other outside forces.
- For example, kerosene rises up in a lamp’s wick without any extra help.
- To drink a soft drink, you need to use your mouth to apply some force, which means capillary action won’t work.
- Blotting paper also works with capillary action because it has a lot of tiny holes that act like tiny tubes.
- Capillary action is used by nature too, like how the small roots of trees act like tubes to get water and nutrients.
|
13. For which one of the following capillarity is not the only reason?
(a) Blotting of ink
(b) Rising of underground water
(c) Spread of water drop on a cotton cloth
(d) Rising of water from the roots of a plant to its foliage
[I.A.S. (Pre) 1999]
Ans. (d) Rising of water from the roots of a plant to its foliage
- We see capillarity in many things we do every day, such as using blotting paper to absorb ink, water that rises up through the ground, water spreading on a cloth, and the way kerosene rises up a lamp’s wick.
- But capillarity isn’t the only thing that makes water rise in a plant from the roots to the leaves – transpiration and cohesion also play a part in this.
|
14. Kerosene rising in the wick of the stove is due to
(a) Osmosis
(b) diffusion
(c) Surface tension
(d) biogen contraction
[R.A.S./R.T.S. (Pre) 1997]
Ans. (c) Surface tension
- The kerosene oil in the stove goes up the wick because of the surface tension of the oil.
- The lamp wick has many small holes that act as tiny tubes, so the kerosene keeps flowing up through these tubes.
|
15. In a capillary tube a fluid rises more as compared to water, this is due to the:
(a) Fluid is more viscous than that of water
(b) The temperature of fluid is more than that of water
(c) Surface tension of fluid is less than that of water
(d) Surface tension of fluid is more than that of water
[R.A.S./R.T.S.(Pre) 2007]
Ans. (d) Surface tension of fluid is more than that of water
- Liquid in a narrow tube will go up higher if it has more surface tension.
- The liquid with the highest surface tension will be the highest.
|
16. When an air bubble at the bottom of the lake rises to the top, it will–
(a) Increased in size
(b) Decreased in size
(c) Maintain its size
(d) Flatten into a disc-like shape
[I.A.S. (pre) 1996]
Ans. (a) Increased in size
- When an air bubble at the bottom of the lake rises up, it will get bigger.
- The pressure of the air inside the bubble will become less because the water it is going through is getting shallower.
|
17. While traveling by plane, the ink of the pen starts to come out–
(a) Due to a decrease in air pressure
(b) Due to increase in air pressure
(c) Due to increase in volume of ink
(d) Due to excessive load.
[U.P.P.C.S. (Pre) 1992]
Ans. (a) Due to a decrease in air pressure
- Fountain pens tend to leak when they are used at high altitudes because the air pressure is lower there.
- This causes the ink inside the pen to have a higher pressure than the atmosphere outside, causing the ink to flow out.
|
18. In automobiles hydraulic brakes work on –
(a) Archimedes Principle
(b) Newton’s law of motion
(c) Bernoulli’s Principle
(d) Pascal’s Law
[Jharkhand P.C.S. (Pre) 2003]
Ans. (d) Pascal’s Law
- Hydraulic brakes, hydraulic presses, and hydraulic elevators all use the same principle as Pascal’s law, which states that any pressure put into a non-squeezable liquid will be spread equally in all directions.
- This means the pressure doesn’t change.
|
19. A sudden fall in barometer reading indicates that the weather will be :
(a) Stormy weather
(b) Rainy weather
(c) Cool dry weather
(d) Hot and humid weather
[I.A.S. (Pre) 2001, U.P.P.C.S. (Pre) 1996]
Ans. (a) Stormy weather
- If the barometer drops quickly, it means a storm is coming.
|
20. Consider the figure of a fountain with four holes, given below :
Which one of the holes in the fountain will throw the water farthest?
(a) 4
(b) 3
(c) 2
(d) 1
[I.A.S. (Pre) 1994]
Ans. (d) 1
- Based on Torricelli’s law, the velocity of efflux is determined by the equation √2gh, where h represents the depth of the hole.
- In the given scenario, hole 1 possesses the greatest depth, resulting in the highest velocity of efflux. Consequently, hole 1 will propel the water the farthest distance.
|
21. A liquid is flowing in a streamlined manner through a cylindrical pipe. Along with a section containing the axis of the pipe, the following profile will be :
[U.P.P.C.S. (Pre) 2003]
Ans. (d)
- The liquid closest to the pipe flows the slowest, and as you move further away from the pipe, the motion speeds up.
|
22. With the rise of temperature, the viscosity of liquid :
(a) Increases
(b) Decreases
(c) Remains unchanged
(d) May increase or decrease depending on the nature of the liquid
[Uttarakhand P.C.S. (Pre) 2016]
Ans. (b) Decreases
- Viscosity is a parameter that quantifies the resistance of a fluid to deformation caused by shear stress or tensile stress.
- In simpler terms, viscosity can be described as the “thickness” or “internal friction” of a fluid.
- The viscosity of water at various temperatures, up to its normal boiling point, is provided in the table below.
- Temperature [°C] Viscosity [mPa.s]
10 1.308
20 1.002
30 0.7978
40 0.6531
50 0.5471
60 0.4668
70 0.4044
80 0.3550
90 0.3150
100 0.2822
- From the data, it is evident that as the temperature increases, the viscosity of the liquid decreases.
|
23. The highest viscosity among the following is:
(a) water
(b) air
(c) blood
(d) honey
(e) None of the above / More than one of the above
[66th B.P.S.C. (Pre) 2020]
Ans. (d) honey
- Viscosity is a measure of how hard it is for a fluid to flow.
- Fluids that are very viscous have more friction so they flow more slowly than those with low viscosity.
- Out of the choices given, honey has the strongest resistance to flow.
|
24. Which one of the following is most viscous?
(a) Alcohol
(b) Water
(c) Honey
(d) Gasoline
[Uttarakhand Lower Sub. (Pre) 2010]
Ans. (c) Honey
- Viscosity is a way to measure how hard it is to change a liquid’s shape or make it stretch.
- Honey is the thickest of all the liquids.
|
25. Assertion (A): With the increase in temperature, the viscosity of glycerin increases.
Reason (R): The rise of temperature increases the kinetic energy of molecules.
Code :
(a) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
[I.A.S. (Pre) 2002]
Ans. (d) (A) is false, but (R) is true.
- As temperature increases, the thickness of a liquid decreases.
- This is because the higher temperature gives the molecules more energy, which makes them move around more.
|
26. The surface of a lake is frozen in severe winter, but the water at its bottom is still liquid. Why?
The following are some options-
(a) Ice is a bad conductor of heat
(b) Since the surface of the lake is at the same temperature as the air, no heat is lost
(c) The density of water is maximum at 4°C
(d) None of the above
[I.A.S. (Pre) 2011]
Ans. (c) The density of water is maximum at 4°C
- Generally, when liquids are heated, they expand, but water is different.
- When heated, the volume of water goes down until it reaches 4°C. After that, when the temperature rises, the water starts to expand.
- At 100°C, it turns into steam. At 4°C, water has the least volume and highest density.
- This strange behavior of water is called anomalous expansion and helps keep the top layers of water in lakes and rivers from freezing when it’s cold outside.
- When the surface temperature drops to 4°C, the water sinks down and the lower layers rise up.
- When the temperature goes below 4°C, the density of the water decreases so it doesn’t sink anymore.
- The surface finally freezes at 0°C while the lower part stays at 4°C, forming a thin layer of ice on top.
|
27. In cold weather, aquatic animals survive even when water at the top layer of the lake freezes into ice because –
(a) They can breathe in ice.
(b) They have enough accumulated oxygen inside them
(c) Their body structure is such that they can survive without oxygen.
(d) Water has the highest density at 4°C so underneath the top layer of ice there is a layer of water.
[U.P.P.C.S. (Pre) 2005]
Ans. (d) Water has the highest density at 4°C so underneath the top layer of ice there is a layer of water.
- This phenomenon is attributed to the occurrence of winter stratification in water bodies.
- During the winter season, the upper layer of water in these bodies becomes extremely cold and eventually freezes.
- However, the lower layers of water remain in a liquid state and maintain a temperature of around 4°C, which is conducive to supporting life.
- Consequently, fishes and other aquatic organisms are protected from the frozen surface layer of water.
- From this observation, it becomes evident that as the temperature rises, the viscosity of the liquid decreases.
|
28. Fish can survive in a frozen lake because –
(a) Fish are warm-blooded animals
(b) Fish hibernate in ice
(c) Water near the bottom does not freeze
(d) Ice is a good conductor of heat
[Jharkhand P.C.S. (Pre) 2010, U.P.P.S.C. (GIC) 2010]
Ans. (c) Water near the bottom does not freeze
- Fish can live in icy lakes because only the surface of the lake gets frozen.
- The water below the ice stays liquid and does not turn into ice.
|
29. Increasing the amount of a substance does not change its–
(a) Volume
(b) Weight
(c) Mass
(d) Density
[U.P.P.C.S. (pre) 1992]
Ans. (d) Density
- The density of an object depends on its mass and volume.
- Density can be found by using the equation :
Density = Mass/Volume
|
30. The density of water will reach its maximum value at the temperature of –
(a) 0ºC
(b) 4º C
(c) 50º C
(d) 100º C
[R.A.S./R.T.S. (Pre) 1992]
Ans. (b) 4º C
- When heating a substance, its mass remains constant, but its volume typically increases.
- As a result, the density of the substance decreases.
- However, water demonstrates an unusual behavior known as anomalous expansion.
- Within a specific temperature range, water exhibits contraction upon heating and expansion upon cooling.
- In the case of water, when it is heated from 0°C, it undergoes contraction between 0°C and 4°C, causing a decrease in volume and an increase in density.
- The volume of water reaches its minimum at 4°C, resulting in the maximum density of water at this temperature.
|
31. At which temperature density of water is maximum?
(a) 4º C
(b) 0º C
(c) –4º C
(d) – 8ºC
[U.P.P.C.S. (Mains) 2008, 43rd B. P.S.C. (Pre) 1999, 42nd B.P.S.C. (Pre) 1998]
Ans. (a) 4º C
- At 4 degrees Celsius (39.2 degrees Fahrenheit), water is the heaviest and most condensed it can be.
|
32. The maximum density of water is at
(a) 373 Kelvin
(b) 277 Kelvin
(c) 273 Kelvin
(d) 269 Kelvin
[U.P.P.C.S. (Mains) 2015]
Ans. (b) 277 Kelvin
- R As the temperature of the water goes up, its density increases and its volume decreases.
- At 4º Celsius, the amount of water is very low and it is most dense.
- 4º Celsius is the same as 4º Kelvin.
- K = C + 273
= 4+ 273 = 277
So, the density of water is maximum at 277K.
|
33. Assertion (A): An iron ball floats on mercury but gets immersed in water.
Reason (R): The specific gravity of iron is more than that of mercury.
Code :
(a) Both (A) and (R) are true and (R) is the correct explanation of (A)
(b) Both (A) and (R) are true but (R) is not a correct explanation of (A)
(c) (A) is true but (R) is false
(d) (A) is false but (R) is true
[I.A.S. (Pre) 2002]
Ans. (c) (A) is true but (R) is false
- A metal ball will float on mercury but sink in water because mercury is heavier than iron.
- Iron is heavier than water, so it sinks when put in water.
- So, statement (A) is accurate but the reason (R) is not.
|
34. Why does an iron nail float on mercury while it sinks in water?
(a) Due to less chemical interaction of iron with mercury than it is with water
(b) Iron is heavier than water and lighter than mercury.
(c) Iron has greater density than water and less than mercury.
(d) Mercury is heavier than water.
[U.P.P.C.S. (Pre) 1994]
Ans. (c) Iron has greater density than water and less than mercury.
- An iron nail floats on mercury because the density of mercury is greater than the density of iron.
- But the density of water is less than that of iron so it sinks in water.
- Because the density of mercury is more than the density of water.
- An object floats in a liquid if its density is lower than that of the liquid.
|
35. A needle sinks in water whereas a ship made of iron floats on it because :
(a) The edge of the needle is pointed
(b) The ship is fat
(c) The ship was driven by a powerful engine
(d) The relative density of the needle is greater than that of water displaced by it
[U.P. Lower Sub. (Spl) (Pre) 2004]
Ans. (d) The relative density of the needle is greater than that of water displaced by it
- Relative density is a comparison of the density of one substance to the density of water.
- Pure water has a relative density of 1.
- If the relative density of a substance is less than 1, it will float in water.
- If it is more than 1, it will sink.
- A ship is made so that its weight is equal to the weight of the water it displaces, making it float.
- An iron needle has a much higher density than water, so it will sink quickly.
|
36. An iron needle floats on the surface of water due to –
(a) Upthrust of water
(b) Surface tension
(c) Viscosity
(d) Gravitational force
[U.P.P.C.S. (Mains) 2012]
Ans. (b) Surface tension
- A needle made of iron can stay above the surface of water because of the surface tension of the water, which is strong enough to balance the weight of the needle.
|
37. While lifting a bucket of water from a well, we feel that the bucket :
(a) Becomes heavier above the surface of water
(b) Becomes lighter above the surface of the water
(c) Loses stability on coming out of the water
(d) Has gained mass on coming out of water
[U.P.P.C.S. (Pre) 2009]
Ans. (a) Becomes heavier above the surface of water
- Archimedes’ principle of flotation states that objects appear to be heavier in the air than when they are in water.
- This is because water pushes up on the object, reducing its weight by the amount of water displaced.
|
38. 200 gm of water is filled in a weightless balloon. Its weight in water will be
(a) Zero
(b) 100 gm
(c) 200 gm
(d) 400 gm
[U.P.R.O./A.R.O (Mains) 2014]
Ans. (a) Zero
- Weight of balloon in water = Weight – Upthrust = 200 – 200 = 0 The balloon is weightless.
|
39. The clouds float in the atmosphere because of their low :
(a) Temperature
(b) Velocity
(c) Pressure
(d) Density
[I.A.S. (Pre) 1995]
Ans. (d) Density
- When water vapor in the air can’t be seen anymore, it turns into tiny drops of water that form clouds.
- These water droplets are so small that gravity has no effect on them.
- Because of this, clouds stay in the air as they are not very heavy.
|
40. While floating in a sea what part of an iceberg is above the surface of the sea?
(a) 1/9
(b) 1/10
(c) 1/6
(d) 1/4
[U.P.P.C.S. (Pre) 2005]
Ans. (a) 1/9
- When pure water freezes at 4 degrees Celsius, the ice is 90% less dense than water.
- This means that 90% of the ice must be below the surface and 10% above.
- Even though sea water is more dense, the ice that forms is still pure and not salty.
- So when an iceberg floats in the sea, only about 1/8 to 1/9 of it is above the surface.
|
41. An ice cube is floating in a glass of water. What happens to the water level when the ice melts? It –
(a) Rises
(b) Falls
(c) Remains the same
(d) First rises and then falls
[M.P.P.C.S. (Pre) 2008]
Ans. (c) Remains the same
- Archimedes’ principle states that any object that is floating in water pushes out the same amount of water as its own weight.
- This means that when an ice cube melts, the water level stays the same.
|
42. A body floats at 4°C water. If the temperature reaches 100°C then-
(a) The body will sink
(b) No change
(c) More parts of the body will submerge
(d) The body will float freely
[M.P.P.C.S. (Pre) 1999]
Ans. (a) The body will sink
- When you heat water, it becomes less dense.
- When the water is 100°C it is the least dense and any object in it will sink.
- When the water is 4°C it is the most dense and any object in it will float.
|
43. Why it is easier to swim in the sea than in a river?
(a) The seawater is salty
(b) The seawater is deep
(c) The seawater is heavier
(d) The sea water is lighter
[U.P. Lower Sub. (Pre) 2002]
Ans. (a) The sea water is salty
- Swimming in the ocean is easier than in a river because the salt in the ocean makes the water denser and provides more buoyancy, making it harder to sink and easier to swim.
|
44. A body weight is highest in which among the following?
(a) Air
(b) Water
(c) Hydrogen
(d) Nitrogen
[U.P. P.C.S. (Mains) 2017]
Ans. (c) Hydrogen
- Hydrogen has a lower upthrust or buoyant force than other materials because it is the lightest gas, so option (c) is the correct answer.
|
45. When a ship enters the sea from a river, what happens?
(a) It rises a little
(b) It remains at the same level
(c) It sinks a little
(d) It is immersed in the bottom of the sea.
[U.P. Lower Sub. (Pre) 2004, U.P. P.C.S. (Pre) 1992]
Ans. (a) It rises a little
- When a boat moves from a river into the ocean, it rises because the saltier ocean water is more dense than the water in the river.
|
46. Assertion (A): When a ship enters a sea from a river, it rises a little.Reason (R): The density of seawater is greater than that of river water.
In the context of the above statements, which of the following is true :
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
[U.P. P.C.S. (Pre) 2003, U.P.U.D.A./L.D.A. (Pre) 2002]
Ans. (a) Both A and R are true and R is the correct explanation of A.
- Seawater is denser than river water, which means that a ship will experience more buoyancy when it is in the sea compared to when it is in a river.
- This causes the ship to rise when it moves from a river to the sea because the volume of the ship in the water decreases to balance out its weight.
|
