Surface Tension MCQ Quiz - Objective Question with Answer for Surface Tension - Download Free PDF

The correct answer is be of spherical shape.

CONCEPT:

EXPLANATION:

• When a water drop falls on the surface of the oil, two forces come into play i.e., the cohesion forces within the water molecules and the other is adhesion forces between oil and water.
• As we know that oil is hydrophobic in nature, therefore, the adhesive forces between oil and water are much weaker compared to the cohesive forces between water and water. 
• Therefore, the water drop on the surface of oil has a tendency to maintain its spherical shape in order to minimize the surface energy.

The correct answer is Cohesive Force between Molecules.

CONCEPT:

• Surface Tension: The tendency of fluid at the surface to reduce its surface area is called surface Tension. 
• Cohesive Force: The force acting between the same molecules of fluid attracting each other is called cohesive force.
  • An example of this is the force between water molecules.
• Adhesive Force: The force acting between different molecules is called adhesive force. 
  • An example of adhesive force is fevicol which is used to stick two things with the help of adhesive force. 

EXPLANATION: 

• The cohesive force acts between molecules of water.
• It tends to contract the surface of a liquid to the smallest possible surface area.
• This causes surface tension in liquid.
• So, the cause of surface tension is the cohesive force between molecules. 

Additional Information

Surface tension can cause small needles to flow on the surface of the water, even if the density of the needle is more than water. 

The correct answer is option 3.

Key Points

• Assertion (A): Relative humidity decreases with increasing air temperature.
  • Correct. Relative humidity is the ratio of the actual amount of water vapor in the air to the maximum amount of water vapor the air can hold at a given temperature.
  • As temperature increases, the air's capacity to hold moisture increases, but if the actual moisture content remains the same, relative humidity decreases.
• Reason (R): Absolute humidity increases with increasing evaporation.
  • Correct. Absolute humidity refers to the total mass of water vapor per unit volume of air.
  • As evaporation increases, more water vapor enters the air, leading to an increase in absolute humidity.
• Conclusion:
  • Both A and R are correct, but R is not the correct explanation of A.
    • A talks about relative humidity (which depends on temperature), while R explains absolute humidity (which depends on evaporation).
• Correct Answer: Both A and R are true, but R is not the correct explanation of A.

The Correct answer is Option 2.

Important Points 

CONCEPT:

• Surface tension: Surface tension is a force per unit length acting in the plane of interface between the liquid and the bounding surface.
  • Its unit is ‘N/m’ and the dimensions are [MT-2].
  • Surface tension is a property that arises due to the intermolecular forces of attraction among the molecules of the liquid.
  • Greater are the intermolecular forces of attraction; higher is the surface tension of that liquid.

EXPLANATION :

• The surface tension decreases as the temperature increases.
• The surface tension of hot water is very less compared to cold water and thus that makes washing clothes easier in hot water
• Hence, option 2 is the answer

The correct answer is The iron rod would float on water surface.

Key Points

•  
• Two primary forces are at play: the downward force of gravity (weight) and the upward force of upthrust (buoyant force).
• The weight of the iron rod is due to its mass and the acceleration due to gravity (W = mg).
• Upthrust is the upward force exerted by a fluid on an immersed or partially immersed object.
• Upthrust is equal to the weight of the fluid displaced by the object (Archimedes' principle).
• The Scenario:
• The question states that the upthrust of the water on the iron rod is greater than the downward force (weight).
• This means the upward force is stronger than the downward force.
• Resultant Force:
• When upthrust is greater than weight, the resultant force on the iron rod is upward.
• This upward force will cause the iron rod to accelerate upward.
• Floating:
• If the iron rod is initially at rest on the water's surface, the excess upthrust will lift it.
• The rod will continue to rise until it reaches a point where the upthrust equals its weight.
• At this point, the rod will float on the water's surface.
• The object will reach an equilibrium point where the weight of the water it displaces is equal to the weight of the object.
• The density of the iron, and the volume of water displaced are the main factors in determining the upthrust.
• If the iron rod was a hollow shape, it would displace more water, thus increasing the upthrust.
• The shape of an object greatly affects its ability to float.
• A solid iron rod has a high density, and therefore it normally sinks.
• For an object to float, the upthrust must be equal to or greater than the objects weight.
• The buoyant force is directly proportional to the density of the fluid.
• The buoyant force is also directly proportional to the volume of the displaced fluid.
• If the water was replaced with a denser fluid, the upthrust would increase.
• The weight of the object is a constant, unless the mass of the object changes.
• The upthrust force is a variable, dependent on the fluid and the volume displaced.
• The concept of upthrust is essential in naval architecture and the design of ships.

The correct answer is obtuse.

CONCEPT:

• Contact angle: The contact angle is a measure of the ability of a liquid to wet the surface of a solid. 

• Adhesive forces: Attractive forces between molecules of different types are called adhesive forces.
• Cohesive forces: Attractive forces between molecules of the same types are called cohesive forces.
• For contact angle 90° the cohesive forces and adhesive forces are in the equilibrium state.

The angle of contact depends on

1. Cleanliness of the surface 
2. Nature of liquid and solid in contact
3. The temperature of the liquid 
4. Medium above the surface of the liquid  

EXPLANATION:

• If a liquid doesn’t wet the glass, the interaction of liquid molecules is greater than the interaction between the liquid and solid molecule, these lead to an obtuse angle of contact. Therefore option 3 is correct.

Important Points

• The angle between 0° and 90° = surface wettable, hydrophilic, cohesive forces are weaker then adhesive forces and the drop will spread on the surface.
• The angle between 90° and 180° = surface not wettable, hydrophobic cohesive forces are stronger than adhesive forces and drop will remain the drop itself.
• The angle is close to 180° = ultra-hydrophobic surface, completely liquid-repellent, lotus effect.
• The contact angle is 90° between water and silver, and cohesive forces and adhesive forces are equal.

The correct answer is Cohesive Force between Molecules.

CONCEPT:

• Surface Tension: The tendency of fluid at the surface to reduce its surface area is called surface Tension. 
• Cohesive Force: The force acting between the same molecules of fluid attracting each other is called cohesive force.
  • An example of this is the force between water molecules.
• Adhesive Force: The force acting between different molecules is called adhesive force. 
  • An example of adhesive force is fevicol which is used to stick two things with the help of adhesive force. 

EXPLANATION: 

• The cohesive force acts between molecules of water.
• It tends to contract the surface of a liquid to the smallest possible surface area.
• This causes surface tension in liquid.
• So, the cause of surface tension is the cohesive force between molecules. 

Additional Information

Surface tension can cause small needles to flow on the surface of the water, even if the density of the needle is more than water. 

The correct answer is be of spherical shape.

CONCEPT:

EXPLANATION:

• When a water drop falls on the surface of the oil, two forces come into play i.e., the cohesion forces within the water molecules and the other is adhesion forces between oil and water.
• As we know that oil is hydrophobic in nature, therefore, the adhesive forces between oil and water are much weaker compared to the cohesive forces between water and water. 
• Therefore, the water drop on the surface of oil has a tendency to maintain its spherical shape in order to minimize the surface energy.

The correct answer is At room temperature, surface tension of water is less than ethyl alcohol. 

Key Points

• Surface tension is indeed typically measured in dynes/cm, which indicates the force required to break a film of length 1 cm. Hence, option 1 is correct.
• The shape of a water droplet is spherical due to surface tension. Hence, option 2 is also correct.
• The spherical shape is the result of surface tension minimizing the surface area of the drop, as the sphere is the shape that has the least surface area for a given volume.
• Contrary to statement 3, at room temperature, the surface tension of water is actually higher than that of ethyl alcohol. For example, water at 20°C has a surface tension of 72.8 dynes/cm, while that for ethyl alcohol is 22.3 dynes/cm.
• The cohesive forces between liquid molecules are indeed responsible for the phenomenon known as surface tension. These forces cause the liquid to behave as though it is covered with a stretched elastic sheet, a property known as surface tension. Hence, option 4 is also correct.

Effect of temperature on surface tension and viscosity:

• As the temperature increases, viscosity decreases.
• Surface tension decreases with an increase in temperature.
• In general, surface tension decreases when the temperature increases because cohesive forces decrease with increased molecular thermal activity.
• The influence of the surrounding environment is due to the adhesive action liquid molecules have at the interface.
• Increasing temperature results in a decrease in viscosity because a larger temperature means particles have greater thermal energy and are more easily overcome the attractive forces binding them together.

CONCEPT:

Surface tension: 

• Surface tension is the property by virtue of which liquid tires to minimize their free surface area.
• In a spherical shape, the surface area is minimum and for this reason, the raindrops are spherical.
• Surface tension is measured as the force acting per unit length of an imaginary line drawn on the liquid surface

\(Surface\;tension = \frac{{Force}}{{length}}\)

EXPLANATION:

• Gravitational force is the force exerted by the earth on an object, gravitational force will only act to pull the insect to the ground hence it won't help the insect to walk on the surface. 
• Insects like water striders are able to walk on the surface due to the high surface tension of the water.
• Water striders use surface tension to their advantage through the highly adapted hydrophobic leg and distributed weight. Hence, option 2 is the answer
• Viscosity is the resistive force acting between the layers of the liquid, Viscosity is the resistive acting between the layers of liquid it won't help the insect to walk on the surface. Hence option 3 is wrong 
• Capillarity is the rise in liquid level against gravity, Capillarity doesn't help the insect to walk on the surface of the water. Hence option 4 is wrong 

Additional Information

• Temperature: If temperature increases then the surface tension of a liquid decreases.
• Soluble Impurities: In the case of less soluble impurities, the surface tension decreases. But, for highly soluble impurities in the liquid the surface tension increases.

The Correct answer is Option 2.

Important Points 

CONCEPT:

• Surface tension: Surface tension is a force per unit length acting in the plane of interface between the liquid and the bounding surface.
  • Its unit is ‘N/m’ and the dimensions are [MT-2].
  • Surface tension is a property that arises due to the intermolecular forces of attraction among the molecules of the liquid.
  • Greater are the intermolecular forces of attraction; higher is the surface tension of that liquid.

EXPLANATION :

• The surface tension decreases as the temperature increases.
• The surface tension of hot water is very less compared to cold water and thus that makes washing clothes easier in hot water
• Hence, option 2 is the answer

The correct answer is Capillarity.

• Kerosene oil rises up in a wick of lantern because of Capillarity.

Important Points

• Capillarity-
  • The tendency of a liquid in a capillary tube or absorbent material to rise or fall as a result of surface tension.
  • One consequence of the pressure difference across a curved liquid-air interface is the well-known effect that water rises up in a narrow tube in spite of gravity.
• The cohesive force between the kerosene and the wick is more compared to the adhesive force of kerosene, so the kerosene rises through the wick due to capillarity.
  • For capillary action, the diameter of the tube should be very small.
  • The liquid rises in the capillary tube due to surface tension.

The correct answer is Capillary Action.

• The phenomenon caused by the falling of liquid in a thin tube is called Capillary Action.

Key Points

• Capillary action: If one end of a capillary tube is put into a liquid that wets glass, it is found that the liquid rises into the capillary tube to a certain height.
• This rise is due to the inward pull of surface tension acting on the surface which pushes the liquid into the capillary tube.
  • When the intermolecular interaction of the solvent itself is significantly inferior to the surface of the material it interacts with, capillary action occurs.
  • It happens only when the binding forces in the liquid are greater than the cohesive forces, which inevitably develop into surface tension.

• The height of the liquid rises or fall (h) is given by
• \({\rm{h}} = \frac{{2{\rm{\;T}}\cos {\rm{\theta }}}}{{{\rm{d\;\rho \;g}}}}\)
• Where T = surface tension, θ = angle of contact, d = diameter of capillary tube, ρ = density of liquid, g = acceleration due gravity

The correct answer is Surface tension.

Key Points

• Surface tension could be defined as the property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the water molecules.
• The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension.
• Surface tension is typically measured in dynes/cm, the force in dynes required to break a film of length 1 cm.
• The surface tension of water is 72 dynes/cm at 25°C. It would take a force of 72 dynes to break a surface film of water 1 cm long.
• Example of Surface tension:
  • ​Walking on water: Small insects such as the water strider can walk on water because their weight is not enough to penetrate the surface.
  • Floating a needle: A carefully placed small needle can be made to float on the surface of the water even though it is several times as dense as water. If the surface is agitated to break up the surface tension, then the needle will quickly sink.
  • Surface tension disinfectants: Disinfectants are usually solutions of low surface tension. This allows them to spread out on the cell walls of bacteria and disrupt them.
  • Why bubbles are round: The surface tension of water provides the necessary wall tension for the formation of bubbles with water. The tendency to minimize that wall tension pulls the bubbles into spherical shapes.
• ​The Gravity of the Spherical Earth:
  • ​Gravity is the force by which a planet or other body draws objects toward its center.
  • The force of gravity keeps all of the planets in orbit around the sun.
  • Anything that has mass also has gravity. Objects with more mass have more gravity. 
  • Gravity also gets weaker with distance.
  • So, the closer objects are to each other, the stronger their gravitational pull is.
  • Earth's gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body.
• The viscosity of the Raindrops/liquid:
  • Viscosity refers to the resistance of a fluid (liquid or gas) to a change in shape, or movement of neighboring portions relative to one another.
  • Viscosity denotes opposition to flow. 
  • The reciprocal of the viscosity is called the fluidity, a measure of the ease of flow. 
  • Molasses has a greater viscosity than water.
  •  The unit of viscosity is newton-second per square meter, which is usually expressed as pascal-second in SI units.
• Atmospheric friction of air molecules:
  • ​ Air resistance describes the forces that are in opposition to the relative motion of an object as it passes through the air.
  • Air friction or air drag is an example of fluid friction.