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NEET Physics: angle of contact Practice Questions

15 free multiple-choice questions on angle of contact (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. If the angle of contact between water and a glass surface is 0°, what does this imply about the interaction between water and glass?

    • AThe water is non-wetting the glass.
    • BThe glass is repelling the water entirely.
    • CThe water is partially wetting the glass.
    • DThe water completely wets the glass.
    Show answer & explanation

    Correct answer: D — The water completely wets the glass.

    A contact angle of 0° signifies perfect wetting, meaning the adhesive forces between the water and glass are perfectly balanced with the cohesive forces within the water, resulting in the liquid spreading completely.

  2. Q2. Surface tension plays a crucial role in determining the angle of contact between a liquid and a solid. Liquids with high surface tension tend to form which type of interaction with the solid surface?

    • AWeak van der Waals forces.
    • BWeak cohesive forces.
    • CStrong cohesive forces.
    • DStrong adhesive forces.
    Show answer & explanation

    Correct answer: D — Strong adhesive forces.

    High surface tension leads to strong adhesive forces between the liquid molecules and the solid surface, which influences the resulting contact angle.

  3. Q3. Which of the following solids generally exhibits a higher contact angle with water compared to a highly hydrophilic substance?

    • APolytetrafluoroethylene (Teflon).
    • BA highly porous sponge saturated with water.
    • CGlass.
    • DWater itself.
    Show answer & explanation

    Correct answer: A — Polytetrafluoroethylene (Teflon).

    Non-polar, low-surface-energy materials like Teflon tend to repel water, resulting in larger contact angles, whereas glass (and hydrophilic materials) interact strongly with water, leading to smaller angles.

  4. Q4. When a liquid forms a concave meniscus on a solid surface, the contact angle is usually greater than 90°. This behavior is characteristic of:

    • Aspontaneous spreading
    • Bstrong adhesion
    • Cpoor wetting
    • Dhigh surface tension
    Show answer & explanation

    Correct answer: C — poor wetting

    A concave meniscus (where the liquid curves away from the solid) occurs when the liquid tends to minimize its surface area, often indicating poor wetting or high surface tension effects.

  5. Q5. Which of the following statements accurately relates the equilibrium of a liquid on a solid based on the angle of contact?

    • Acos θ= (γ₍LG) - γ₍SG))/(γ₍SL))
    • Bcos θ= (γ₍SG))/(γ₍SL))
    • Ccos θ= (γ₍SG) - γ₍SL))/(γ₍LG))
    • Dcos θ= (γ₍SL) - γ₍SG))/(γ₍LG))
    Show answer & explanation

    Correct answer: D — cos θ= (γ₍SL) - γ₍SG))/(γ₍LG))

    The relationship governing the equilibrium of interfacial tensions (Young's equation) is cos θ= (γ₍SG) - γ₍SL))/(γ₍LG)), where γ represents the surface tensions of the solid-gas, solid-liquid, and liquid-gas interfaces, respectively.

  6. Q6. When a liquid completely wets a solid surface, the angle of contact (θ) is typically:

    • ALess than 90°
    • BEqual to 90°
    • CUndefined
    • DGreater than 90°
    Show answer & explanation

    Correct answer: A — Less than 90°

    Complete wetting occurs when the adhesive forces are stronger than the cohesive forces, causing the liquid to spread over the surface. This results in a contact angle less than 90 degrees.

  7. Q7. The contact angle is typically measured within the liquid phase where the liquid meets the solid surface. Which physical quantity does the contact angle primarily describe?

    • AThe curvature of the liquid surface
    • BThe balance of interfacial tensions
    • CThe density variation
    • DThe bulk modulus
    Show answer & explanation

    Correct answer: B — The balance of interfacial tensions

    The angle of contact is a geometric measure that describes the equilibrium state determined by the balance of the three interfacial tensions (γ₍SL), γ₍SG), γ₍LG)).

  8. Q8. The angle of contact is a measure of the interaction between the liquid and the solid surface. What does a contact angle of 0° signify?

    • AThe liquid is completely repelled by the solid.
    • BThe liquid exhibits maximum surface tension.
    • CThe liquid is partially wetting the solid.
    • DThe liquid completely wets the solid surface.
    Show answer & explanation

    Correct answer: D — The liquid completely wets the solid surface.

    A contact angle of 0° means the liquid spreads out completely over the solid surface, indicating perfect wetting.

  9. Q9. In a scenario where a liquid is held in a groove formed by two solid plates, the contact angle geometry is influenced by the balance between which two types of intermolecular forces?

    • Aonly adhesive forces
    • Bonly cohesive forces
    • Ccohesive and adhesive forces
    • Dvan der Waals forces only
    Show answer & explanation

    Correct answer: C — cohesive and adhesive forces

    The shape and equilibrium state of a liquid confined between solid boundaries depend on the competition between the cohesive forces (liquid-liquid attraction) and the adhesive forces (liquid-solid attraction).

  10. Q10. If the solid surface energy is very high and the liquid-solid interaction is strong, the resulting angle of contact (θ) will generally be:

    • Aexactly 90°
    • Bvery small (θ≈ 0°)
    • Cundefined
    • Dlarge (θ> 90°)
    Show answer & explanation

    Correct answer: B — very small (θ≈ 0°)

    High solid surface energy means strong adhesion between the liquid and the solid, leading to a tendency for the liquid to spread out and minimize contact area, resulting in a very small contact angle.

  11. Q11. For a liquid to exhibit good wetting on a solid surface, the balance between adhesive forces and cohesive forces must be favorable. This condition is related to which term?

    • ASurface tension of the liquid
    • BIntermolecular forces
    • CSurface energy of the solid
    • DAngle of contact being small
    Show answer & explanation

    Correct answer: D — Angle of contact being small

    Good wetting (small contact angle) occurs when the adhesive forces (liquid-solid attraction) are greater than the cohesive forces (liquid-liquid attraction), which is reflected in a small contact angle.

  12. Q12. If a liquid exhibits a small contact angle (less than 90°) on a solid, this usually implies that the liquid and the solid have which type of intermolecular interaction?

    • ARepulsive interaction.
    • BHigh cohesive interaction.
    • CStrongly immiscible interaction.
    • DStrong adhesive interaction.
    Show answer & explanation

    Correct answer: D — Strong adhesive interaction.

    A small contact angle indicates good wetting, which is caused by strong adhesive forces between the liquid and the solid surface.

  13. Q13. A liquid placed on a solid surface forms a contact angle of 90°. This condition implies that the intermolecular forces between the liquid and the solid are:

    • ACohesive forces are greater than adhesive forces
    • BAdhesive forces are equal to cohesive forces
    • CAdhesive forces are greater than cohesive forces
    • DCohesive forces are less than adhesive forces
    Show answer & explanation

    Correct answer: B — Adhesive forces are equal to cohesive forces

    When the contact angle is 90°, the adhesive forces between the liquid and the solid are exactly balanced by the cohesive forces within the liquid. This state is known as perfect wetting or ideal spreading, where the liquid spreads evenly over the surface.

  14. Q14. Consider a substance that completely wets a surface, resulting in an angle of contact of 0°. This situation primarily demonstrates which property of the liquid-solid system?

    • AHigh surface energy of the solid.
    • BLow surface tension of the liquid.
    • CHigh cohesive forces of the liquid.
    • DStrong adhesive forces between the liquid and the solid.
    Show answer & explanation

    Correct answer: D — Strong adhesive forces between the liquid and the solid.

    A 0° contact angle implies complete wetting, which is a direct consequence of strong adhesive forces between the liquid and the solid surface.

  15. Q15. The angle of contact is defined as the angle formed between the liquid surface and the solid surface in equilibrium. What physical property governs this angle?

    • ASurface energy of the solid
    • BCohesion within the liquid
    • CSurface tension of the liquid
    • DAdhesion between liquid and solid
    Show answer & explanation

    Correct answer: D — Adhesion between liquid and solid

    The angle of contact is determined by the balance of intermolecular forces, which involves both the cohesive forces within the liquid and the adhesive forces between the liquid and the solid. Adhesion is the primary factor influencing the wetting behavior related to the contact angle.

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