60. Which situation most directly follows Newton’s law of cooling?
[UPSC NDA-II GAT, September 2024]
(A) Melting of ice at constant temperature
(B) Cooling of hot coffee in a room
(C) Boiling water at constant pressure
(D) Expansion of a heated metal rod
Answer: (B) Cooling of hot coffee in a room
Explanation: Newton’s law of cooling relates the rate of heat loss approximately to the temperature difference between an object and its surroundings, under suitable conditions. A hot cup of coffee therefore cools quickly initially, then more slowly as it approaches room temperature.
59. Which example represents convection of heat?
[UPSC CDS-II General Knowledge, September 2024]
(A) Microwave heating of food
(B) Water circulating while boiling in a pot
(C) Feeling solar warmth outdoors
(D) Heating the far end of a brass rod
Answer: (B) Water circulating while boiling in a pot
Explanation: In boiling water, warmer regions become less dense and rise, while cooler water descends. This bulk fluid movement transfers energy by convection. Heat spreading along a stationary metal rod is conduction; warmth from sunlight is received by radiation.
58. Which statement about water is incorrect?
[UPSC NDA-I GAT, April 2024]
(A) Water has relatively high specific heat
(B) The latent heat of fusion of water is very low
(C) Liquid water is denser than ice
(D) Pure water is a poor electrical conductor
Answer: (B) The latent heat of fusion of water is very low
Explanation: Water has unusually high specific heat and significant latent heat of fusion. These properties moderate changes of temperature and allow ice to absorb considerable energy while melting. Ice is less dense than water, so it generally floats on the surface.
57. At what temperature do Celsius and Fahrenheit scales show the same numerical reading?
[SSC MTS, October 2024]
(A) 40°
(B) 32°
(C) −40°
(D) −32°
Answer: (C) −40°
Explanation: The conversion is F = 9C/5 + 32. Setting Fahrenheit and Celsius readings equal yields C = −40. Thus −40°C and −40°F represent the same temperature; the scales have different zero points and degree sizes.
56. What is the name given to −273.15°C?
[SSC MTS, October 2024]
(A) Absolute zero
(B) Standard temperature
(C) Zero-point energy
(D) Freezing point of water
Answer: (A) Absolute zero
Explanation: Absolute zero is 0 kelvin, equivalent to −273.15°C. It represents the lower limit of thermodynamic temperature. Quantum mechanical systems retain zero-point motion, so absolute zero should not be interpreted as every atom becoming completely motionless.
55. What is the direct transition from a solid to a gas called?
[SSC MTS, November 2024]
(A) Sublimation
(B) Fusion
(C) Evaporation
(D) Condensation
Answer: (A) Sublimation
Explanation: Sublimation bypasses the liquid phase as solid particles escape into the gaseous state. Camphor, dry ice and iodine provide familiar examples under suitable conditions. The reverse process, vapour depositing directly as solid, is called deposition.
54. Identify the incorrect statement concerning evaporation and boiling.
[SSC MTS, October 2024]
(A) Boiling is a bulk phenomenon
(B) Both boiling and evaporation take place only throughout the liquid
(C) Evaporation is a surface phenomenon
(D) Evaporation can cause cooling
Answer: (B) Both boiling and evaporation take place only throughout the liquid
Explanation: Boiling forms vapour bubbles throughout a liquid; evaporation occurs only from its exposed surface. Evaporation can proceed below the boiling point and removes energetic molecules, producing cooling. Therefore describing both mechanisms as exclusively bulk processes is incorrect.
53. Why is water stored in an earthen pot often cooler? Identify the incorrect explanation.
[SSC CGL Tier-I, September 2024]
(A) Water evaporates from its outer surface
(B) The pot contains fine pores
(C) Atmospheric water vapour enters the pot and provides the cooling
(D) Some water seeps through pores and evaporates
Answer: (C) Atmospheric water vapour enters the pot and provides the cooling
Explanation: Tiny pores allow a small amount of water to seep to the pot’s outside. As that moisture evaporates, it absorbs latent heat from the remaining water and vessel. The cooling does not depend on outside vapour entering the pot.
52. What is horizontal heat transfer associated with the movement of air called?
[SSC Selection Post, June 2024]
(A) Conduction
(B) Advection
(C) Variation
(D) Convection only
Answer: (B) Advection
Explanation: Advection transports heat horizontally with moving air or water. Convection commonly describes vertical circulation driven by density differences, while conduction transfers energy through microscopic collisions. In the atmosphere, warm and cold air advection strongly influence local temperature changes.
51. Which process is the reverse of solidification?
[SSC CPO, June 2024]
(A) Fusion or melting
(B) Vaporisation
(C) Sublimation
(D) Condensation
Answer: (A) Fusion or melting
Explanation: Solidification changes liquid into solid and generally releases latent heat. Melting, also termed fusion, reverses this transition and requires an energy input at the melting temperature. Condensation and vaporisation concern the liquid-gas boundary rather than the solid-liquid boundary.
