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NEET Physics: application of surface tension Practice Questions

15 free multiple-choice questions on application of surface tension (Properties of Solids and Liquids) for NEET Physics, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. The phenomenon of surface tension primarily arises due to the imbalance of forces acting on the molecules at the surface of a liquid. What causes this imbalance?

    • AThe net inward pull of cohesive forces
    • BThe inward pull of gravity
    • CAttractive forces from the bulk liquid
    • DThe balance between cohesion and adhesion
    Show answer & explanation

    Correct answer: A — The net inward pull of cohesive forces

    Surface tension arises because the molecules in the bulk of the liquid are pulled equally in all directions by neighboring molecules (cohesive forces). At the surface, molecules only experience inward cohesive forces, leading to a net inward pull (surface tension).

  2. Q2. Which of the following scenarios is primarily governed by the application of surface tension?

    • ACapillary action and droplet formation
    • BThe boiling point of a liquid
    • CThe viscosity of a liquid
    • DThe density of a gas
    Show answer & explanation

    Correct answer: A — Capillary action and droplet formation

    Capillary action (rise/depression) and the formation of droplets are direct macroscopic manifestations of the effects of surface tension.

  3. Q3. Capillary action, where a liquid rises or falls in a narrow tube, is a direct manifestation of the interplay between which two forces?

    • AAdhesion and Cohesion
    • BSurface tension and Density
    • CCohesion and Pressure
    • DViscosity and Surface tension
    Show answer & explanation

    Correct answer: A — Adhesion and Cohesion

    Capillary action occurs because the adhesive forces between the liquid and the tube walls (adhesion) are balanced against the cohesive forces within the liquid (cohesion) and the surface tension forces.

  4. Q4. When the surface tension of a liquid is reduced, what happens to the droplet formed by the liquid?

    • AThe surface tension decreases, leading to a flatter shape
    • BThe droplet shape becomes more spherical
    • CThe droplet surface becomes more irregular
    • DThe droplet volume increases
    Show answer & explanation

    Correct answer: A — The surface tension decreases, leading to a flatter shape

    Reduced surface tension means the cohesive forces are weaker, allowing the surface to deform more easily, resulting in a flatter shape (less curvature) under the same external forces.

  5. Q5. If two liquids A and B are in contact, and the surface tension of A is significantly higher than B, what is the tendency for liquid A to interact with liquid B?

    • AThe interaction is solely governed by density
    • BLiquid A will be strongly attracted to Liquid B
    • CLiquid A will repel Liquid B
    • DLiquid A will try to minimize contact with Liquid B
    Show answer & explanation

    Correct answer: B — Liquid A will be strongly attracted to Liquid B

    Higher surface tension indicates stronger cohesive forces. The liquid with higher surface tension will exhibit a stronger tendency to minimize its surface area, leading to stronger attractive interactions with the surrounding medium.

  6. Q6. If the surface tension of a liquid is reduced, the intermolecular forces within the liquid are generally:

    • ABecome zero
    • BDecreased
    • CIncreased
    • DRemained unchanged
    Show answer & explanation

    Correct answer: B — Decreased

    Surface tension is a measure of the energy required to increase the surface area, which is related to the cohesive forces. A reduction in surface tension implies a reduction in these cohesive forces.

  7. Q7. Surface tension is the property of a liquid surface due to:

    • AIntermolecular forces between liquid and air
    • BCohesion of molecules only
    • CAdhesion of molecules only
    • DCohesive forces between molecules only
    Show answer & explanation

    Correct answer: B — Cohesion of molecules only

    Surface tension arises due to the net inward cohesive forces acting on the molecules at the surface of the liquid, where they experience less cohesive attraction from the bulk liquid.

  8. Q8. Surface tension is defined as the force acting on a unit length of the surface. What is the SI unit of surface tension?

    • AN/m
    • BNewton (N)
    • CPascal (Pa)
    • DJoule (J)
    Show answer & explanation

    Correct answer: C — Pascal (Pa)

    Surface tension is a force, and the SI unit of force is the Newton (N). Since the definition involves force per unit length, the unit is Newton per meter (N/m), which is equivalent to the Pascal (Pa) in this context (or N/m).

  9. Q9. Which physical property is primarily responsible for the existence of surface tension in a liquid?

    • APressure gradient inside the liquid
    • BGravitational force acting on the volume
    • CIntermolecular forces at the surface
    • DKinetic energy of the molecules
    Show answer & explanation

    Correct answer: C — Intermolecular forces at the surface

    Surface tension arises due to the net inward cohesive forces acting on the molecules at the surface, where molecules are less constrained, leading to a net inward pull.

  10. Q10. The phenomenon of wetting is governed by the balance between cohesive forces within the liquid and adhesive forces between the liquid and the solid surface. If the adhesive force is much greater than the cohesive force, the liquid will tend to:

    • ASpread out completely (wetting)
    • BRemain in a droplet shape
    • CSpherically rise
    • DMaintain a high contact angle
    Show answer & explanation

    Correct answer: A — Spread out completely (wetting)

    When adhesion is stronger than cohesion, the liquid spreads over the surface, resulting in complete wetting.

  11. Q11. Capillary rise occurs when the liquid wets the solid surface due to the interplay of which forces?

    • AAdhesion and cohesion only
    • BCohesion and surface tension
    • CAdhesion and surface tension
    • DSurface tension and gravity
    Show answer & explanation

    Correct answer: C — Adhesion and surface tension

    Capillary rise is governed by the balance between the adhesive forces (liquid-solid attraction) and the cohesive forces (liquid-liquid attraction), mediated by the surface tension.

  12. Q12. When a liquid is placed in contact with a solid surface, the balance between cohesive forces within the liquid and adhesive forces between the liquid and the solid determines the angle of contact. This angle is known as:

    • AAngle of contact
    • BMeniscus angle
    • CContact angle
    • DAngle of repose
    Show answer & explanation

    Correct answer: C — Contact angle

    The angle formed between the liquid surface and the solid surface when they meet is called the contact angle, which is directly related to the balance of surface tension and intermolecular forces.

  13. Q13. If the temperature of a liquid increases, what generally happens to its surface tension?

    • AIt decreases because intermolecular attractive forces weaken
    • BIt increases due to increased molecular kinetic energy
    • CIt increases because the cohesive forces become stronger
    • DIt remains unchanged as surface tension is independent of temperature
    Show answer & explanation

    Correct answer: A — It decreases because intermolecular attractive forces weaken

    As temperature increases, the kinetic energy of the molecules increases, causing the cohesive forces holding them together to become weaker, thus decreasing the surface tension.

  14. Q14. Surface tension is a property that arises due to the cohesive forces acting at the surface of a liquid. What force does surface tension primarily represent?

    • AAdhesive forces only
    • BGravitational forces
    • CBoth cohesive and adhesive forces
    • DCohesive forces only
    Show answer & explanation

    Correct answer: C — Both cohesive and adhesive forces

    Surface tension is the net force acting parallel to the surface due to the cohesive forces of the liquid molecules attempting to minimize the surface area.

  15. Q15. Which of the following liquids generally has a higher surface tension than water at the same temperature?

    • AMethanol
    • BAcetone
    • CWater
    • DEthanol
    Show answer & explanation

    Correct answer: B — Acetone

    Acetone (a non-polar organic solvent) generally exhibits a higher surface tension than water (a polar solvent) due to different intermolecular forces.

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