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NEET Physics: Surface energy and surface tension Practice Questions

15 free multiple-choice questions on Surface energy and 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 energy required to increase the surface area of a liquid is directly related to which property?

    • ADensity of the liquid
    • BSurface tension
    • CCompressibility of the liquid
    • DVolume of the liquid
    Show answer & explanation

    Correct answer: B — Surface tension

    Surface energy (or surface tension energy) is proportional to the total surface area exposed. Increasing the surface area requires more energy input.

  2. Q2. The phenomenon of surface tension causes liquids to minimize their surface area. This tendency is due to the molecules trying to achieve a state of:

    • AMinimum potential energy
    • BMaximum kinetic energy
    • CMinimum surface energy
    • DMaximum cohesive force
    Show answer & explanation

    Correct answer: C — Minimum surface energy

    Liquids minimize their surface area because the system naturally seeks the state of lowest potential energy, which corresponds to minimizing the surface energy.

  3. Q3. When a liquid droplet is formed, it assumes a spherical shape because:

    • Athe droplet minimizes its volume
    • Bthe liquid minimizes its total surface energy
    • Cgravity is balanced by surface tension forces
    • Dthe liquid seeks to maximize its contact with the container walls
    Show answer & explanation

    Correct answer: B — the liquid minimizes its total surface energy

    The spherical shape minimizes the total surface area for a given volume, thus minimizing the total surface energy (and consequently surface tension).

  4. Q4. The surface energy of a liquid is essentially the energy stored in the molecular bonds at the interface. Which term best describes the energy stored in the region at the surface?

    • APotential Energy
    • BSurface Potential
    • CKinetic Energy
    • DCohesive Energy
    Show answer & explanation

    Correct answer: B — Surface Potential

    Surface energy is the energy stored per unit area at the interface, representing the potential energy stored in the molecular interactions at that boundary.

  5. Q5. When a liquid is in equilibrium on a solid surface, the balance of forces along the contact line is governed by the relationship between surface tension and the forces exerted by the solid. If a liquid has a specific surface energy, what property dictates the shape it assumes when the contact angle is formed?

    • AThe volume of the liquid droplet.
    • BThe density of the liquid.
    • CThe magnitude of the cohesive forces within the liquid.
    • DThe balance between surface tension and the solid-liquid interfacial tensions.
    Show answer & explanation

    Correct answer: D — The balance between surface tension and the solid-liquid interfacial tensions.

    The equilibrium shape of a liquid droplet on a surface is determined by the balance of interfacial tensions (surface tensions) acting at the contact line, which is directly related to the liquid's surface energy.

  6. Q6. The force experienced by a unit length of the surface of a liquid is known as:

    • ASurface tension
    • BSurface energy
    • CCohesion
    • DPressure
    Show answer & explanation

    Correct answer: A — Surface tension

    Surface tension is defined as the force acting tangentially per unit length along the surface of the liquid.

  7. Q7. For a liquid to spread across a surface, the balance between surface tension and the intermolecular forces exerted by the substrate must be considered. This balance is often quantified by the contact angle.

    • ATrue
    • BDepends on viscosity
    • CFalse
    • DOnly for solids
    Show answer & explanation

    Correct answer: A — True

    The contact angle determines the equilibrium state of the liquid droplet on a solid surface, directly reflecting the interplay between surface tension and interfacial forces.

  8. Q8. Which of the following statements correctly describes the relationship between surface tension and intermolecular forces?

    • ASurface tension is directly proportional to the attractive forces between molecules.
    • BSurface tension is inversely proportional to the cohesive forces.
    • CSurface tension is independent of the intermolecular forces.
    • DSurface tension is the manifestation of the net cohesive forces acting at the surface.
    Show answer & explanation

    Correct answer: D — Surface tension is the manifestation of the net cohesive forces acting at the surface.

    Surface tension arises because molecules at the surface experience a net inward cohesive force, which opposes the expansion of the surface.

  9. Q9. Surface tension arises due to the cohesive forces acting on the molecules at the surface of a liquid. These forces are primarily caused by:

    • AGravitational forces acting downwards
    • BIntermolecular forces within the bulk liquid
    • CRepulsive forces between adjacent molecules
    • DAdhesive forces between the liquid and the container walls
    Show answer & explanation

    Correct answer: B — Intermolecular forces within the bulk liquid

    Surface tension is the result of the net inward cohesive forces exerted on the molecules at the surface of the liquid, which are due to intermolecular forces.

  10. Q10. The force acting on a unit length of the surface of a liquid is known as surface tension. This force is due to:

    • Athe gravitational pull acting on the molecules
    • Bthe attractive forces between adjacent liquid molecules
    • Cthe external pressure exerted by the container
    • Dthe cohesive forces within the bulk liquid
    Show answer & explanation

    Correct answer: B — the attractive forces between adjacent liquid molecules

    Surface tension arises because the liquid molecules at the surface are attracted inward by the molecules below them, resulting in a net inward force per unit length along the surface.

  11. Q11. If the cohesive forces within a liquid are very strong, the surface tension of the liquid will be:

    • Azero
    • Bincreased
    • Cdecreased
    • Dunchanged
    Show answer & explanation

    Correct answer: B — increased

    Stronger cohesive forces mean the molecules strongly attract each other, leading to a higher force acting along the surface, thus increasing the surface tension.

  12. Q12. Surface tension acts tangentially along the boundary between the liquid and the surrounding medium. This type of force is known as:

    • AAdhesive force
    • BSurface tension force
    • CCohesive force
    • DGravitational force
    Show answer & explanation

    Correct answer: B — Surface tension force

    Surface tension is the net tangential force acting along the interface of the liquid surface.

  13. Q13. If the temperature of a liquid is increased, how does the surface tension generally change?

    • AIt remains unchanged
    • BIt becomes zero
    • CIt decreases
    • DIt increases
    Show answer & explanation

    Correct answer: C — It decreases

    As temperature increases, the kinetic energy of the molecules increases, weakening the cohesive forces and thus decreasing the surface tension.

  14. Q14. Surface energy is associated with the energy required to create a unit area of surface. This energy is related to:

    • Athe work done in creating the surface
    • Bthe density of the liquid
    • Cthe volume of the substance
    • Dthe temperature of the liquid
    Show answer & explanation

    Correct answer: A — the work done in creating the surface

    Surface energy is the energy stored in the system due to the formation of the surface; it is the energy required to create that surface area.

  15. Q15. 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.

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