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501. A capillary tube of radius $0.5 \, mm$ is dipped in water ($T = 0.072 \, N/m, \rho = 1000 \, kg/m^3, g = 9.8 \, m/s^2$). Assuming $\theta = 0^\circ$, calculate the rise of water in the tube.
ⓐ. 1.0 cm
ⓑ. 2.9 cm
ⓒ. 4.2 cm
ⓓ. 5.5 cm
Correct Answer: 2.9 cm
Explanation: $h = \frac{2T \cos \theta}{\rho g r}$.
Substitute: $h = \frac{2 \times 0.072 \times 1}{1000 \times 9.8 \times 0.0005} \approx 0.029 \, m = 2.9 \, cm$.
502. A capillary of radius $0.25 \, mm$ shows a rise of $6 \, cm$ in water at $20^\circ C$. Calculate surface tension.
ⓐ. 0.060 N/m
ⓑ. 0.072 N/m
ⓒ. 0.080 N/m
ⓓ. 0.090 N/m
Correct Answer: 0.072 N/m
Explanation: Rearranging formula: $T = \frac{h \rho g r}{2 \cos \theta}$.
$T = \frac{0.06 \times 1000 \times 9.8 \times 0.00025}{2} \approx 0.072 \, N/m$.
503. A soap bubble of radius $2 \, mm$ has excess pressure of $72 \, Pa$. Calculate surface tension.
ⓐ. 0.018 N/m
ⓑ. 0.036 N/m
ⓒ. 0.072 N/m
ⓓ. 0.144 N/m
Correct Answer: 0.018 N/m
Explanation: For soap bubble: $\Delta P = \frac{4T}{r}$.
So, $T = \frac{\Delta P \cdot r}{4} = \frac{72 \times 0.002}{4} = 0.018 \, N/m$.
504. The excess pressure inside a water droplet of radius $1 \, mm$ is $150 \, Pa$. Find surface tension.
ⓐ. 0.0375 N/m
ⓑ. 0.050 N/m
ⓒ. 0.075 N/m
ⓓ. 0.100 N/m
Correct Answer: 0.075 N/m
Explanation: For droplet: $\Delta P = \frac{2T}{r}$.
$T = \frac{\Delta P \cdot r}{2} = \frac{150 \times 0.001}{2} = 0.075 \, N/m$.
505. A soap bubble of diameter $4 \, cm$ has surface tension $0.04 \, N/m$. Find excess pressure inside.
ⓐ. 2 Pa
ⓑ. 4 Pa
ⓒ. 8 Pa
ⓓ. 16 Pa
Correct Answer: 8 Pa
Explanation: Radius = 0.02 m. For bubble, $\Delta P = \frac{4T}{r}$.
$\Delta P = \frac{4 \times 0.04}{0.02} = 8 \, Pa$.
506. A liquid rises to height $h = 5 \, cm$ in a capillary of radius $0.4 \, mm$. If $\rho = 1000 \, kg/m^3, g = 9.8 \, m/s^2, \theta = 0^\circ$, find surface tension.
ⓐ. 0.078 N/m
ⓑ. 0.082 N/m
ⓒ. 0.092 N/m
ⓓ. 0.098 N/m
Correct Answer: 0.082 N/m
Explanation: $T = \frac{h \rho g r}{2 \cos \theta} = \frac{0.05 \times 1000 \times 9.8 \times 0.0004}{2} \approx 0.082 \, N/m$.
507. A water droplet of radius $0.5 \, mm$ has surface tension $0.072 \, N/m$. Find excess pressure inside the droplet.
ⓐ. 144 Pa
ⓑ. 200 Pa
ⓒ. 288 Pa
ⓓ. 500 Pa
Correct Answer: 288 Pa
Explanation: For droplet: $\Delta P = \frac{2T}{r}$.
$\Delta P = \frac{2 \times 0.072}{0.0005} = 288 \, Pa$.
508. If the surface tension of a liquid is $0.05 \, N/m$, calculate the work required to increase its surface area by $40 \, cm^2$.
ⓐ. 1.5 mJ
ⓑ. 2.0 mJ
ⓒ. 2.5 mJ
ⓓ. 3.0 mJ
Correct Answer: 2.0 mJ
Explanation: Work = $T \times \Delta A$.
$W = 0.05 \times 40 \times 10^{-4} = 2.0 \times 10^{-3} \, J = 2.0 \, mJ$.
509. A spherical raindrop of radius $0.5 \, mm$ has surface tension $0.072 \, N/m$. Calculate excess pressure inside.
ⓐ. 200 Pa
ⓑ. 250 Pa
ⓒ. 288 Pa
ⓓ. 300 Pa
Correct Answer: 288 Pa
Explanation: Same as Q507, since formula is same for droplet: $\Delta P = \frac{2T}{r} = \frac{2 \times 0.072}{0.0005} = 288 \, Pa $.
510. Two soap bubbles of radii $2 \, cm$ and $4 \, cm$ are joined by a tube. Which bubble will shrink?
ⓐ. Both remain same
ⓑ. Larger bubble
ⓒ. Smaller bubble
ⓓ. Neither
Correct Answer: Smaller bubble
Explanation: Excess pressure $\Delta P = 4T/r$. Smaller bubble has higher internal pressure, so air flows into larger bubble, making smaller one shrink.
511. Surface energy of a liquid surface is defined as:
ⓐ. Energy required to increase the pressure of liquid
ⓑ. Work done to increase the surface area of liquid by unity
ⓒ. Energy due to viscosity of liquid
ⓓ. Energy per unit volume of liquid
Correct Answer: Work done to increase the surface area of liquid by unity
Explanation: Surface energy is the work required to increase the surface area of a liquid by $1 \, m^2$. It is equal to surface tension numerically.
512. The SI unit of surface energy is:
ⓐ. N/m
ⓑ. J/m²
ⓒ. N/m²
ⓓ. J/m
Correct Answer: J/m²
Explanation: Surface energy is energy per unit area. Since energy is in joules and area in $m^2$, the unit is J/m².
513. Which of the following statements is correct about surface energy and surface tension?
ⓐ. Both are unrelated
ⓑ. Surface energy per unit area = surface tension
ⓒ. Surface energy = surface tension × volume
ⓓ. Surface tension is always greater than surface energy
Correct Answer: Surface energy per unit area = surface tension
Explanation: Work done in increasing area by unit value is numerically equal to surface tension, so both quantities are equivalent.
514. Which physical phenomenon proves the existence of surface energy?
ⓐ. Buoyant force
ⓑ. Spherical shape of liquid droplets
ⓒ. Viscosity of fluids
ⓓ. Diffusion in liquids
Correct Answer: Spherical shape of liquid droplets
Explanation: Drops become spherical to minimize surface energy, since a sphere has minimum surface area for a given volume.
515. When two soap bubbles of equal size coalesce, the surface energy:
ⓐ. Increases
ⓑ. Decreases
ⓒ. Remains constant
ⓓ. Becomes zero
Correct Answer: Decreases
Explanation: The total surface area decreases when bubbles merge, hence surface energy decreases and excess energy is released.
516. Which of the following is an example of surface energy in daily life?
ⓐ. A floating needle on water
ⓑ. Capillary rise in a tube
ⓒ. Expansion of soap films
ⓓ. All of the above
Correct Answer: All of the above
Explanation: All these phenomena involve work done against surface forces, demonstrating surface energy.
517. The relation between surface tension (T) and surface energy (E) is:
ⓐ. $E = T \times r$
ⓑ. $E = T \times V$
ⓒ. $E = T \times A$
ⓓ. $E = \frac{T}{A}$
Correct Answer: $E = T \times A$
Explanation: Surface energy is proportional to total surface area of the liquid, with $T$ being surface tension and $A$ surface area.
518. Why does a soap film contract after formation?
ⓐ. To increase density
ⓑ. To reduce volume
ⓒ. To minimize surface energy
ⓓ. To balance buoyancy
Correct Answer: To minimize surface energy
Explanation: Soap films shrink because nature tends to minimize energy, achieved by reducing surface area.
519. The work required to double the surface area of a soap film of area $A$ and surface tension $T$ is:
ⓐ. $TA$
ⓑ. $2TA$
ⓒ. $4TA$
ⓓ. $\frac{TA}{2}$
Correct Answer: $2TA$
Explanation: For a soap film, there are two surfaces (inside and outside). Work required = $\Delta W = 2 T \Delta A = 2T A$.
520. Which factor determines the surface energy of a liquid?
ⓐ. Cohesive forces between molecules
ⓑ. Gravitational forces on molecules
ⓒ. Buoyant forces in liquid
ⓓ. Compressibility of liquid
Correct Answer: Cohesive forces between molecules
Explanation: Surface energy is caused by imbalance of cohesive forces at the liquid surface, which creates energy per unit area.
521. The relationship between surface energy and surface tension is:
ⓐ. Surface energy per unit length = surface tension
ⓑ. Surface energy per unit volume = surface tension
ⓒ. Surface energy per unit area = surface tension
ⓓ. Surface energy = surface tension × volume
Correct Answer: Surface energy per unit area = surface tension
Explanation: Surface tension is defined as force per unit length, and surface energy is work done per unit area. Numerically, they are equal.
522. If the surface area of a liquid film increases by $\Delta A$, the work done is:
ⓐ. $W = T \Delta A$
ⓑ. $W = 2T \Delta A$
ⓒ. $W = \tfrac{T}{\Delta A}$
ⓓ. $W = T^2 \Delta A$
Correct Answer: $W = 2T \Delta A$
Explanation: A soap film has two surfaces (inner and outer). Work done = $2T \Delta A$.
523. A liquid has surface tension $0.06 \, N/m$. If the surface area increases by $0.02 \, m^2$, calculate the work done.
ⓐ. $1.2 \times 10^{-3} J$
ⓑ. $2.4 \times 10^{-3} J$
ⓒ. $6.0 \times 10^{-3} J$
ⓓ. $1.2 \times 10^{-2} J$
Correct Answer: $2.4 \times 10^{-3} J$
Explanation: Work = $2 T \Delta A = 2 \times 0.06 \times 0.02 = 0.0024 \, J$.
524. The energy required to form a bubble of radius $r$ and surface tension $T$ is:
ⓐ. $4 \pi r^2 T$
ⓑ. $8 \pi r^2 T$
ⓒ. $2 \pi r^2 T$
ⓓ. $\pi r^2 T$
Correct Answer: $8 \pi r^2 T$
Explanation: A soap bubble has two surfaces. Energy = surface tension × total surface area = $T \times (2 \times 4 \pi r^2) = 8 \pi r^2 T$.
525. If surface tension of water is $0.072 \, N/m$, find surface energy per unit area.
ⓐ. 0.036 J/m²
ⓑ. 0.072 J/m²
ⓒ. 0.144 J/m²
ⓓ. 1.0 J/m²
Correct Answer: 0.072 J/m²
Explanation: Numerically, surface tension and surface energy per unit area are equal, so both have same magnitude.
526. Why does stretching a soap film require energy?
ⓐ. To increase density
ⓑ. To increase gravitational potential
ⓒ. To increase surface energy proportional to new area
ⓓ. To decrease adhesion
Correct Answer: To increase surface energy proportional to new area
Explanation: Work must be done against surface tension to create additional area, which is stored as surface energy.
527. A cubic film frame of side $10 \, cm$ is dipped in soap solution. Calculate the surface energy if surface tension is $0.04 \, N/m$.
ⓐ. 0.0740 J
ⓑ. 0.0042 J
ⓒ. 0.5343 J
ⓓ. 0.0048 J
Correct Answer: 0.0048 J
Explanation: Surface area = $6a^2 = 6(0.1^2) = 0.06 \, m^2$. For two surfaces, $2T A = 2 \times 0.04 \times 0.06 = 0.0048 \, J$.
528. The work required to blow a soap bubble of radius $1 \, cm$ with surface tension $0.05 \, N/m$ is:
ⓐ. $0.003 J$
ⓑ. $0.006 J$
ⓒ. $0.009 J$
ⓓ. $0.012 J$
Correct Answer: $0.006 J$
Explanation: Energy = $8 \pi r^2 T = 8 \pi (0.01^2)(0.05) \approx 0.006 J$.
529. Which statement is correct about the relation between surface tension and surface energy?
ⓐ. Both are independent properties
ⓑ. Both arise from cohesive forces between molecules
ⓒ. Surface energy decreases as surface tension increases
ⓓ. Surface tension is unrelated to molecular interactions
Correct Answer: Both arise from cohesive forces between molecules
Explanation: Cohesive forces at the liquid surface create tension and energy, making both concepts interdependent.
530. A square wire frame of side $20 \, cm$ is dipped into a soap solution and lifted out, forming a soap film. If surface tension is $0.04 \, N/m$, find the work required to break the film.
ⓐ. 0.032 J
ⓑ. 0.064 J
ⓒ. 0.080 J
ⓓ. 0.096 J
Correct Answer: 0.064 J
Explanation: Area = $a^2 = 0.2^2 = 0.04 \, m^2$. For two surfaces: work = $2TA = 2 \times 0.04 \times 0.04 = 0.064 J$.
531. Which property of liquids is utilized in producing waterproof coatings on fabrics?
ⓐ. Buoyancy
ⓑ. Surface tension and surface energy control
ⓒ. Viscosity
ⓓ. Diffusion
Correct Answer: Surface tension and surface energy control
Explanation: Waterproof coatings reduce wettability by lowering adhesion between water and fabric, controlled by modifying surface energy.
532. Why do paints spread more uniformly on walls when mixed with turpentine?
ⓐ. Turpentine increases viscosity
ⓑ. Turpentine lowers surface tension of paint
ⓒ. Turpentine increases surface energy
ⓓ. Turpentine increases adhesion to glass only
Correct Answer: Turpentine lowers surface tension of paint
Explanation: Lower surface tension improves wetting of rough wall surfaces, allowing paint to spread evenly.
533. Nanomaterials such as self-cleaning glass (Lotus effect) rely on:
ⓐ. Very high viscosity
ⓑ. Low Reynolds number
ⓒ. Modification of surface energy
ⓓ. Strong buoyant force
Correct Answer: Modification of surface energy
Explanation: Hydrophobic coatings alter surface energy so water forms droplets and rolls off, carrying dirt away.
534. Why do detergents and soaps clean oily clothes effectively?
ⓐ. They increase density of water
ⓑ. They reduce water’s surface tension and alter surface chemistry
ⓒ. They increase viscosity of water
ⓓ. They neutralize buoyant forces
Correct Answer: They reduce water’s surface tension and alter surface chemistry
Explanation: Detergent molecules lower surface tension, penetrate grease, and emulsify oil, enabling removal in washing.
535. In metallurgy, why is surface tension important?
ⓐ. It affects crystal lattice energy
ⓑ. It determines the shape and solidification of molten metals
ⓒ. It decreases melting point
ⓓ. It increases viscosity of metals
Correct Answer: It determines the shape and solidification of molten metals
Explanation: Surface tension influences droplet formation, solidification, and wetting properties critical in welding and casting processes.
536. In pharmaceuticals, surface tension is reduced in liquid medicines to:
ⓐ. Increase drug density
ⓑ. Increase solubility and absorption
ⓒ. Reduce viscosity
ⓓ. Increase surface energy only
Correct Answer: Increase solubility and absorption
Explanation: Lower surface tension enhances spreading and penetration of drug solutions, improving bioavailability.
537. Why are nanoparticles effective as catalysts in surface chemistry?
ⓐ. They have high mass
ⓑ. They have lower density
ⓒ. They provide large surface area with high surface energy
ⓓ. They eliminate viscosity
Correct Answer: They provide large surface area with high surface energy
Explanation: High surface energy at nanoscale enhances adsorption and reaction rates, making nanoparticles efficient catalysts.
538. Adhesives stick better to surfaces when:
ⓐ. The liquid’s surface energy is much greater than the solid’s
ⓑ. The liquid’s surface energy is close to or lower than the solid’s
ⓒ. Surface tension is maximum
ⓓ. Density is maximum
Correct Answer: The liquid’s surface energy is close to or lower than the solid’s
Explanation: For good adhesion, the adhesive must wet the surface effectively, which occurs when surface energy balance favors spreading.
539. Why is surface chemistry important in corrosion studies?
ⓐ. Corrosion only depends on density
ⓑ. Corrosion involves surface reactions with oxygen and moisture
ⓒ. Corrosion depends only on viscosity
ⓓ. Surface energy has no role in corrosion
Correct Answer: Corrosion involves surface reactions with oxygen and moisture
Explanation: Surface chemistry explains corrosion as an electrochemical process at the interface of metal, air, and water.
540. In material science, why do fine powders tend to form clumps?
ⓐ. Because of gravity
ⓑ. Because of cohesive forces due to surface energy
ⓒ. Because of buoyant forces
ⓓ. Because of viscosity
Correct Answer: Because of cohesive forces due to surface energy
Explanation: High surface area of fine powders increases cohesive forces, causing particles to stick together into lumps.
541. The angle of contact is defined as the angle between:
ⓐ. The tangent to the liquid surface and the vertical wall of the container
ⓑ. The tangent to the liquid surface at the point of contact and the solid surface inside the liquid
ⓒ. The horizontal liquid surface and the wall of the container
ⓓ. The vertical axis of the tube and the surface of the liquid
Correct Answer: The tangent to the liquid surface at the point of contact and the solid surface inside the liquid
Explanation: Angle of contact is measured inside the liquid between the tangent to the meniscus and the solid surface, showing wetting behavior.
542. If the angle of contact $\theta < 90^\circ$, the liquid:
ⓐ. Does not wet the solid surface
ⓑ. Partially wets the solid surface
ⓒ. Perfectly wets the solid surface
ⓓ. Forms a convex meniscus
Correct Answer: Perfectly wets the solid surface
Explanation: When $\theta < 90^\circ$, adhesive forces dominate, the liquid wets the surface and forms a concave meniscus.
543. If the angle of contact $\theta > 90^\circ$, the liquid:
ⓐ. Perfectly wets the surface
ⓑ. Does not wet the surface and forms a convex meniscus
ⓒ. Flows rapidly through capillaries
ⓓ. Shows zero adhesion
Correct Answer: Does not wet the surface and forms a convex meniscus
Explanation: For mercury-glass ($\theta \approx 135^\circ$), cohesive forces dominate, producing a convex meniscus.
544. The angle of contact between pure water and clean glass is approximately:
ⓐ. $0^\circ$
ⓑ. $30^\circ$
ⓒ. $60^\circ$
ⓓ. $90^\circ$
Correct Answer: $0^\circ$
Explanation: Pure water wets clean glass completely, leading to an angle of contact close to $0^\circ$.
545. The angle of contact between mercury and glass is about:
ⓐ. $30^\circ$
ⓑ. $60^\circ$
ⓒ. $90^\circ$
ⓓ. $135^\circ$
Correct Answer: $135^\circ$
Explanation: Mercury does not wet glass, and due to stronger cohesive forces, the angle of contact is obtuse, around $135^\circ$.
546. Which instrument is used to measure the angle of contact accurately?
ⓐ. Microscope
ⓑ. Goniometer
ⓒ. Manometer
ⓓ. Viscometer
Correct Answer: Goniometer
Explanation: A goniometer measures the contact angle formed by a liquid on a solid surface to study wetting properties.
547. Which of the following factors affects the angle of contact?
ⓐ. Nature of the liquid
ⓑ. Nature of the solid surface
ⓒ. Impurities present in the liquid
ⓓ. All of the above
Correct Answer: All of the above
Explanation: Contact angle depends on both liquid and solid surface properties, as well as the presence of impurities or detergents.
548. In capillary action, the rise of liquid is possible only if the angle of contact is:
ⓐ. Less than $90^\circ$
ⓑ. Equal to $90^\circ$
ⓒ. Greater than $90^\circ$
ⓓ. Independent of angle
Correct Answer: Less than $90^\circ$
Explanation: Capillary rise requires a concave meniscus, which occurs when the liquid wets the surface ($\theta < 90^\circ$).
549. For a liquid-solid interface, the relation between surface tensions and contact angle is given by:
ⓐ. $T_{LS} = T_{SV} + T_{LV} \cos \theta$
ⓑ. $T_{SV} = T_{LS} + T_{LV} \cos \theta$
ⓒ. $T_{LV} = T_{LS} + T_{SV} \cos \theta$
ⓓ. $T_{SV} = T_{LV} + T_{LS} \cos \theta$
Correct Answer: $T_{SV} = T_{LS} + T_{LV} \cos \theta$
Explanation: Young’s equation relates the solid-vapor ($T_{SV}$), liquid-solid ($T_{LS}$), and liquid-vapor ($T_{LV}$) surface tensions with the angle of contact.
550. When detergent is added to water, the angle of contact with glass:
ⓐ. Increases
ⓑ. Decreases
ⓒ. Remains the same
ⓓ. Becomes $180^\circ$
Correct Answer: Decreases
Explanation: Detergents reduce surface tension and increase adhesion between water and glass, decreasing the angle of contact and enhancing wetting.
551. A zero contact angle indicates that the liquid:
ⓐ. Does not wet the solid at all
ⓑ. Partially wets the solid
ⓒ. Completely wets the solid surface
ⓓ. Forms a convex meniscus
Correct Answer: Completely wets the solid surface
Explanation: When $\theta = 0^\circ$, adhesive forces dominate completely, and the liquid spreads fully on the solid, showing perfect wetting.
552. An acute contact angle ($0^\circ < \theta < 90^\circ$) means:
ⓐ. The liquid partially wets the surface with concave meniscus
ⓑ. The liquid does not wet the surface
ⓒ. The liquid forms a convex meniscus
ⓓ. The liquid spreads infinitely
Correct Answer: The liquid partially wets the surface with concave meniscus
Explanation: When $\theta < 90^\circ$, adhesive forces exceed cohesive forces, leading to partial but significant wetting and concave meniscus.
553. An obtuse contact angle ($90^\circ < \theta < 180^\circ$) signifies that:
ⓐ. The liquid perfectly wets the surface
ⓑ. The liquid does not wet the surface well
ⓒ. The liquid forms a flat meniscus
ⓓ. The liquid becomes superfluid
Correct Answer: The liquid does not wet the surface well
Explanation: Obtuse angles occur when cohesive forces dominate adhesive forces, leading to poor wetting and convex meniscus.
554. Which of the following is an example of zero contact angle?
ⓐ. Water on clean glass
ⓑ. Mercury on glass
ⓒ. Oil on waxed surface
ⓓ. Water on greasy surface
Correct Answer: Water on clean glass
Explanation: Pure water wets clean glass completely, producing a contact angle close to $0^\circ$.
555. Mercury in a glass capillary tube shows a contact angle of about:
ⓐ. $0^\circ$ (zero)
ⓑ. $60^\circ$ (acute)
ⓒ. $135^\circ$ (obtuse)
ⓓ. $180^\circ$ (flat)
Correct Answer: $135^\circ$ (obtuse)
Explanation: Mercury’s cohesive forces dominate over adhesion with glass, producing a convex meniscus and obtuse angle.
556. If a liquid has an acute angle of contact, then in a capillary tube it will:
ⓐ. Rise
ⓑ. Depress
ⓒ. Remain unchanged
ⓓ. Oscillate
Correct Answer: Rise
Explanation: With $\theta < 90^\circ$, adhesion dominates, leading to concave meniscus and capillary rise (e.g., water in glass).
557. If a liquid has an obtuse angle of contact, then in a capillary tube it will:
ⓐ. Rise
ⓑ. Depress
ⓒ. Remain unchanged
ⓓ. Form zero curvature
Correct Answer: Depress
Explanation: With $\theta > 90^\circ$, cohesion dominates, leading to convex meniscus and depression of liquid (e.g., mercury in glass).
558. Which of the following corresponds to complete non-wetting of a surface?
ⓐ. $\theta = 0^\circ$
ⓑ. $\theta = 45^\circ$
ⓒ. $\theta = 90^\circ$
ⓓ. $\theta = 180^\circ$
Correct Answer: $\theta = 180^\circ$
Explanation: At $\theta = 180^\circ$, liquid does not wet the surface at all, staying as a spherical droplet.
559. Water on a wax-coated leaf shows contact angle closer to:
ⓐ. $0^\circ$
ⓑ. $30^\circ$
ⓒ. $100^\circ$
ⓓ. $180^\circ$
Correct Answer: $100^\circ$
Explanation: Wax is hydrophobic, so water forms droplets with obtuse angles, typically around $100^\circ$.
560. Superhydrophobic surfaces, such as lotus leaves, have contact angles:
ⓐ. $< 30^\circ$
ⓑ. $30^\circ–60^\circ$
ⓒ. $90^\circ–120^\circ$
ⓓ. $> 150^\circ$
Correct Answer: $> 150^\circ$
Explanation: On superhydrophobic surfaces, water forms nearly spherical droplets with contact angles above $150^\circ$, causing self-cleaning “lotus effect.”
561. The ability of oil to spread over water is due to:
ⓐ. Oil’s low viscosity
ⓑ. Oil’s lower surface tension compared to water
ⓒ. Oil’s higher density
ⓓ. Buoyant force of water
Correct Answer: Oil’s lower surface tension compared to water
Explanation: Liquids with lower surface tension spread over liquids with higher surface tension. Oil spreads over water because $T_{oil} < T_{water}$.
562. Wetting of glass by water is an example of:
ⓐ. Cohesion dominating adhesion
ⓑ. Adhesion dominating cohesion
ⓒ. Zero contact angle with no wetting
ⓓ. Non-wetting liquid
Correct Answer: Adhesion dominating cohesion
Explanation: Water molecules are strongly attracted to glass molecules, giving concave meniscus and capillary rise (wetting).
563. Which of the following phenomena is due to poor wetting?
ⓐ. Water spreading on glass
ⓑ. Mercury rising in glass
ⓒ. Water rising in capillaries
ⓓ. Detergent spreading in water
Correct Answer: Mercury rising in glass
Explanation: Mercury does not wet glass ($\theta \approx 135^\circ$), resulting in poor wetting and capillary depression.
564. Detergents help in cleaning action because they:
ⓐ. Increase cohesion of water molecules
ⓑ. Increase adhesion and reduce surface tension
ⓒ. Increase density of water
ⓓ. Reduce viscosity
Correct Answer: Increase adhesion and reduce surface tension
Explanation: Detergents reduce surface tension of water and enhance adhesion to oily or greasy surfaces, enabling spreading and cleaning.
565. The “Lotus Effect,” where water droplets roll off leaves carrying dirt, is due to:
ⓐ. High density of water
ⓑ. Superhydrophobic surface with very high contact angle
ⓒ. Low viscosity of water
ⓓ. Capillary rise in leaf pores
Correct Answer: Superhydrophobic surface with very high contact angle
Explanation: Lotus leaves have waxy microstructures giving contact angles $> 150^\circ$, preventing wetting and aiding self-cleaning.
566. Why does kerosene spread easily on water?
ⓐ. It has higher viscosity
ⓑ. Its density is higher than water
ⓒ. It has lower surface tension than water
ⓓ. It has higher cohesion than adhesion
Correct Answer: It has lower surface tension than water
Explanation: Liquids with lower surface tension spread on higher tension surfaces, so kerosene spreads on water.
567. Capillary action in soil helps plants absorb water because:
ⓐ. Soil repels water
ⓑ. Soil pores act as capillaries, aiding wetting
ⓒ. Cohesion prevents absorption
ⓓ. Density of water decreases in soil
Correct Answer: Soil pores act as capillaries, aiding wetting
Explanation: Water wets soil particles and rises in capillary pores, providing water supply to plant roots.
568. In ink pens, capillary action works effectively when:
ⓐ. Ink has low density
ⓑ. Ink wets the nib material (acute angle of contact)
ⓒ. Ink is non-wetting (obtuse angle of contact)
ⓓ. Ink surface tension is maximum
Correct Answer: Ink wets the nib material (acute angle of contact)
Explanation: Capillary rise occurs only when $\theta < 90^\circ$. Ink wets nib surfaces, ensuring smooth flow.
569. Waterproof jackets are designed by making fabric surfaces:
ⓐ. Hydrophilic with acute angles
ⓑ. Hydrophobic with obtuse or near 180° angles
ⓒ. Porous with capillary rise
ⓓ. Strongly adhesive to water
Correct Answer: Hydrophobic with obtuse or near 180° angles
Explanation: Waterproofing requires water repellence, achieved by making surfaces hydrophobic with large contact angles.
570. Why does water spread on a clean glass surface but form droplets on an oily surface?
ⓐ. Adhesion is stronger with glass, weaker with oil
ⓑ. Cohesion dominates in both cases
ⓒ. Water density is greater on glass
ⓓ. Glass reduces viscosity of water
Correct Answer: Adhesion is stronger with glass, weaker with oil
Explanation: On clean glass, adhesion dominates and water spreads. On oily surfaces, cohesion dominates, so water beads into droplets.
571. The spherical shape of small liquid drops is due to:
ⓐ. Gravity
ⓑ. Buoyant force
ⓒ. Surface tension minimizing surface area
ⓓ. Viscosity
Correct Answer: Surface tension minimizing surface area
Explanation: A sphere has the least surface area for a given volume. Surface tension pulls molecules inward, creating spherical drops.
572. Why do larger drops flatten at the bottom instead of remaining spherical?
ⓐ. Because of viscosity
ⓑ. Because gravity dominates over surface tension
ⓒ. Because adhesion becomes zero
ⓓ. Because buoyant force increases
Correct Answer: Because gravity dominates over surface tension
Explanation: For large drops, gravitational force exceeds surface tension, distorting the spherical shape and flattening them.
573. Which force resists the expansion of a soap bubble?
ⓐ. Gravity
ⓑ. Cohesive force → Surface tension
ⓒ. Viscosity only
ⓓ. Buoyancy
Correct Answer: Cohesive force → Surface tension
Explanation: Surface tension acts inward, opposing expansion of soap bubbles and stabilizing their surface.
574. The excess pressure inside a soap bubble of radius $r$ is:
ⓐ. $\Delta P = \frac{2T}{r}$
ⓑ. $\Delta P = \frac{3T}{r}$
ⓒ. $\Delta P = \frac{4T}{r}$
ⓓ. $\Delta P = \frac{T}{r}$
Correct Answer: $\Delta P = \frac{4T}{r}$
Explanation: For soap bubbles (two surfaces), excess pressure is $\Delta P = \frac{4T}{r}$.
575. For a water droplet of radius $r$, excess pressure inside is:
ⓐ. $\Delta P = \frac{2T}{r}$
ⓑ. $\Delta P = \frac{T}{r}$
ⓒ. $\Delta P = \frac{4T}{r}$
ⓓ. $\Delta P = \frac{3T}{r}$
Correct Answer: $\Delta P = \frac{2T}{r}$
Explanation: A droplet has one surface; hence excess pressure is $\Delta P = \frac{2T}{r}$.
576. Why are soap bubbles more stable than pure liquid bubbles?
ⓐ. Soap increases density
ⓑ. Soap decreases surface tension and balances internal/external pressure better
ⓒ. Soap increases viscosity only
ⓓ. Soap reduces buoyancy
Correct Answer: Soap decreases surface tension and balances internal/external pressure better
Explanation: Soap films reduce surface tension, making bubbles easier to form and more stable than pure water bubbles.
577. Which factor is responsible for collapse of small bubbles faster than large ones?
ⓐ. Greater buoyancy
ⓑ. Greater viscosity
ⓒ. Higher internal pressure due to small radius
ⓓ. Higher adhesion
Correct Answer: Higher internal pressure due to small radius
Explanation: From $\Delta P = \frac{4T}{r}$, smaller $r$ gives higher pressure, so small bubbles shrink faster.
578. When two bubbles of unequal radii are connected, air flows:
ⓐ. From large to small bubble
ⓑ. From small to large bubble
ⓒ. Both ways equally
ⓓ. No flow occurs
Correct Answer: From small to large bubble
Explanation: Smaller bubbles have higher pressure. Air flows from higher pressure (small bubble) to lower pressure (large bubble).
579. Why do raindrops not grow indefinitely large?
ⓐ. Cohesion becomes zero at high size
ⓑ. Surface tension reduces with altitude
ⓒ. Gravitational force overcomes surface tension and breaks large drops
ⓓ. Viscosity limits their size
Correct Answer: Gravitational force overcomes surface tension and breaks large drops
Explanation: When size increases, weight dominates, leading to breakage into smaller drops.
580. The stability of foams (collection of bubbles) depends on:
ⓐ. Surface tension alone
ⓑ. Viscosity of liquid and surface tension reduction by surfactants
ⓒ. Buoyant forces of air
ⓓ. Density difference between air and liquid
Correct Answer: Viscosity of liquid and surface tension reduction by surfactants
Explanation: Foams are stabilized by surfactants that lower surface tension and by liquid viscosity which slows bubble collapse.
581. Why are soap bubbles spherical in shape?
ⓐ. Gravity pulls equally in all directions
ⓑ. Surface tension acts equally along the surface, minimizing area
ⓒ. Air pressure is uniform inside
ⓓ. Buoyant force balances pressure
Correct Answer: Surface tension acts equally along the surface, minimizing area
Explanation: Surface tension tends to minimize surface area, and for a given volume, the sphere has the minimum surface area.
582. A water droplet forms a spherical shape in air mainly due to:
ⓐ. Atmospheric pressure
ⓑ. Viscosity of water
ⓒ. Surface tension
ⓓ. Gravity
Correct Answer: Surface tension
Explanation: Cohesive forces at the liquid surface pull molecules inward, producing a spherical drop to minimize energy.
583. Why does a raindrop become flattened while falling through the air?
ⓐ. Because of low surface tension
ⓑ. Because of buoyancy
ⓒ. Because of air resistance opposing spherical shape
ⓓ. Because of adhesion to air
Correct Answer: Because of air resistance opposing spherical shape
Explanation: While surface tension makes drops spherical, air drag distorts them and flattens the bottom as size increases.
584. When a soap bubble is blown larger, its internal pressure:
ⓐ. Increases
ⓑ. Decreases
ⓒ. Remains constant
ⓓ. Becomes zero
Correct Answer: Decreases
Explanation: Excess pressure inside bubble is $\Delta P = \tfrac{4T}{r}$. As radius increases, pressure decreases.
585. Two bubbles of radii $r_1 < r_2$ are connected by a tube. Which statement is correct?
ⓐ. Air flows from large bubble to small bubble
ⓑ. Air flows from small bubble to large bubble
ⓒ. No flow occurs
ⓓ. Both bubbles collapse
Correct Answer: Air flows from small bubble to large bubble
Explanation: Smaller bubbles have higher internal pressure due to smaller radius, so air flows into the larger bubble.
586. If surface tension of water decreases due to detergent, the shape of droplets formed will be:
ⓐ. More spherical
ⓑ. Less spherical and more irregular
ⓒ. Completely cubic
ⓓ. Unchanged
Correct Answer: Less spherical and more irregular
Explanation: Lower surface tension weakens cohesive forces, preventing perfect spherical drops.
587. Which factor determines the curvature of a liquid drop?
ⓐ. Gravity only
ⓑ. Ratio of cohesive to adhesive forces
ⓒ. Buoyancy
ⓓ. Density of the liquid only
Correct Answer: Ratio of cohesive to adhesive forces
Explanation: Drop curvature depends on balance of cohesive (inward pull) and adhesive forces (interaction with surroundings).
588. Why does mercury form a convex meniscus in glass tubes?
ⓐ. Adhesion dominates
ⓑ. Cohesion dominates, pulling molecules inward
ⓒ. Buoyancy increases
ⓓ. Density decreases
Correct Answer: Cohesion dominates, pulling molecules inward
Explanation: Mercury has strong cohesive forces compared to adhesion with glass, producing a convex surface.
589. Why does water form a concave meniscus in a glass tube?
ⓐ. Cohesion dominates
ⓑ. Adhesion between water and glass dominates over cohesion
ⓒ. Buoyancy dominates
ⓓ. Gravity dominates
Correct Answer: Adhesion between water and glass dominates over cohesion
Explanation: Strong adhesion between water and glass pulls the liquid upward along walls, forming a concave meniscus.
590. In bubbles, why is the pressure inside greater than outside?
ⓐ. Because buoyant force pushes air inside
ⓑ. Because of the inward pull of surface tension on the thin film
ⓒ. Because of high viscosity of liquid
ⓓ. Because gravity compresses it
Correct Answer: Because of the inward pull of surface tension on the thin film
Explanation: Surface tension tends to contract the bubble film, creating excess internal pressure compared to outside air.
591. In medical ultrasound imaging, microbubbles are used as contrast agents because:
ⓐ. They increase viscosity of blood
ⓑ. They scatter and reflect ultrasound waves strongly
ⓒ. They increase blood pressure
ⓓ. They absorb ultrasound waves completely
Correct Answer: They scatter and reflect ultrasound waves strongly
Explanation: Microbubbles with gas cores have large acoustic impedance mismatch with tissues, enhancing ultrasound contrast.
592. Which property of bubbles is most important in ultrasound imaging?
ⓐ. High density
ⓑ. High thermal conductivity
ⓒ. Resonance with ultrasound frequencies
ⓓ. Viscosity
Correct Answer: Resonance with ultrasound frequencies
Explanation: Bubbles oscillate (expand and contract) near ultrasound frequency, enhancing signal contrast in imaging.
593. In bubble dynamics, the collapse of bubbles in a liquid (cavitation) can be harmful because:
ⓐ. It decreases density of liquid
ⓑ. It produces high local pressures and temperatures
ⓒ. It increases viscosity permanently
ⓓ. It reduces buoyancy
Correct Answer: It produces high local pressures and temperatures
Explanation: Cavitation bubble collapse generates shock waves that damage ship propellers, turbines, and pumps.
594. Which engineering application requires minimizing cavitation (bubble collapse)?
ⓐ. Inkjet printing
ⓑ. Hydraulic turbines and ship propellers
ⓒ. Spray painting
ⓓ. Foam production
Correct Answer: Hydraulic turbines and ship propellers
Explanation: Cavitation erosion reduces efficiency and damages metal surfaces in high-speed fluid machinery.
595. Why are bubbles used in drug delivery systems in medicine?
ⓐ. They reduce drug viscosity
ⓑ. They serve as carriers that can be burst with ultrasound to release drugs
ⓒ. They increase drug density
ⓓ. They dissolve instantly in blood
Correct Answer: They serve as carriers that can be burst with ultrasound to release drugs
Explanation: Microbubbles can encapsulate drugs and release them at targeted tissues using ultrasound bursts.
596. In bubble dynamics, what causes a bubble to oscillate in a fluid?
ⓐ. Buoyant forces
ⓑ. Viscous drag
ⓒ. Pressure variations in the surrounding fluid
ⓓ. Gravitational force
Correct Answer: Pressure variations in the surrounding fluid
Explanation: Variations in external pressure cause bubbles to expand and contract rhythmically.
597. Which engineering system uses controlled bubbles to enhance mixing and chemical reactions?
ⓐ. Car engines
ⓑ. Bubble column reactors
ⓒ. Hydraulic brakes
ⓓ. Jet turbines
Correct Answer: Bubble column reactors
Explanation: In chemical engineering, gas bubbles are passed through liquids to promote mixing and improve reaction rates.
598. In ultrasound imaging, stability of bubbles is improved by:
ⓐ. Using air bubbles only
ⓑ. Coating bubbles with biocompatible shells (lipids or polymers)
ⓒ. Increasing viscosity of blood
ⓓ. Reducing surface tension to zero
Correct Answer: Coating bubbles with biocompatible shells (lipids or polymers)
Explanation: Shell coatings prevent rapid dissolution, making bubbles stable long enough for diagnostic imaging.
599. Which phenomenon in bubble dynamics is useful in cleaning delicate instruments (like surgical tools)?
ⓐ. Foam spreading
ⓑ. Cavitation in ultrasonic cleaners
ⓒ. Capillary rise
ⓓ. Meniscus formation
Correct Answer: Cavitation in ultrasonic cleaners
Explanation: Ultrasound creates collapsing bubbles that release energy, scrubbing and cleaning tiny surfaces effectively.
600. Why do cavitation bubbles near a solid surface cause severe damage?
ⓐ. They reduce density of liquid
ⓑ. They implode asymmetrically, producing micro-jets against the surface
ⓒ. They absorb surface energy
ⓓ. They increase wetting of the surface
Correct Answer: They implode asymmetrically, producing micro-jets against the surface
Explanation: Bubble collapse near a surface creates high-speed liquid jets and shock waves, leading to pitting and material erosion.
The chapter Mechanical Properties of Fluids holds a crucial position in Class 11 Physics (NCERT/CBSE syllabus). It explains advanced topics like fluid motion, applications of Bernoulli’s principle, and surface tension, which are significant in both board exams and competitive exams including JEE, NEET, and state-level tests. The entire chapter is covered through 700 MCQs with solutions, split into 7 systematic parts. In this Part 6, you will practice another 100 questions with explanations, designed to test both concepts and numerical skills.
- 👉 Total MCQs in this chapter: 700.
- 👉 This page contains: Sixth set of 100 solved MCQs.
- 👉 Great for board exams, JEE, NEET, and other competitive tests.
- 👉 To browse other chapters or classes, use the navigation bar above.
- 👉 For the last set of questions, proceed to the Part 7 button above.