Q1. SI unit of heat is ________.
Ans: Joule (J)
Q2. SI unit of temperature is ________.
Ans: Kelvin (K)
Q3. The device used to measure temperature is ________.
Ans: Thermometer
Q4. 0 °C = ________ K
Ans: 273 K
Q5. 100 °C = ________ K
Ans: 373 K
Q6. Heat flows from ________ body to ________ body.
Ans: Hotter, colder
Q7. Conduction occurs mainly in ________.
Ans: Solids
Q8. Convection occurs in ________.
Ans: Liquids and gases
Q9. Radiation does not require ________.
Ans: Medium
Q10. Good conductor of heat: (a) wood (b) copper (c) plastic
Ans: Copper
Q11. Poor conductor of heat is called ________.
Ans: Insulator
Q12. Land and sea breeze are due to ________.
Ans: Convection
Q13. Dark-colored clothes absorb ________ heat.
Ans: More
Q14. White-colored clothes absorb ________ heat.
Ans: Less
Q15. Boiling point of water = ________ °C.
Ans: 100 °C
Q16. Normal human body temperature = ________ °C.
Ans: 37 °C
Q17. Latent heat of fusion of ice = ________ J/kg.
Ans: 3.34 × 10⁵ J/kg
Q18. Latent heat of vaporization of water = ________ J/kg.
Ans: 2.26 × 10⁶ J/kg
Q19. Heat = ____ × ____× ____
Ans: Mass × Specific heat × Temperature change
Q20. SI unit of specific heat capacity = ________.
Ans: J/kg·K
Q21. Heat transfer by radiation occurs at _____ speed.
Ans: Speed of light
Q22. True/False: Metals expand on heating.
Ans: True
Q23. Expansion of liquids is used in ________.
Ans: Thermometers
Q24. The sensation of hotness or coldness is called ________.
Ans: Temperature
Q25. Heat absorbed without rise in temperature is called ________.
Ans: Latent heat
Q26. Device used in cold countries to heat rooms = ________.
Ans: Heater (convection currents)
Q27. SI unit of thermal conductivity = ________.
Ans: W/m·K
Q28. A body that absorbs all radiation is called ________.
Ans: Black body
Q29. A polished surface is a ________ absorber of heat.
Ans: Poor
Q30. Vacuum flask reduces heat loss by ________.
Ans: Conduction, convection, radiation
Short & Long Answer Questions
Q31. Define heat.
Ans: Heat is a form of energy that flows from a hotter body to a colder body.
Q32. Differentiate between heat and temperature.
Ans: Heat is energy (J), temperature is measure of hotness (°C, K).
Q33. State three methods of heat transfer.
Ans: Conduction, convection, radiation.
Q34. Explain conduction with example.
Ans: Heat transfer in solids, e.g., heating one end of metal rod.
Q35. Explain convection with example.
Ans: Heat transfer in liquids/gases, e.g., boiling water, sea breeze.
Q36. Explain radiation with example.
Ans: Heat transfer without medium, e.g., sunlight reaching Earth.
Q37. Why are cooking utensils made of metal but handles of wood/plastic?
Ans: Metal = good conductor, handle = insulator.
Q38. Why are woollen clothes worn in winter?
Ans: Wool traps air, reduces heat loss.
Q39. Why is water a poor conductor of heat?
Ans: Heat transfers slowly in liquids by convection.
Q40. Why do land breezes blow at night?
Ans: Land cools faster than sea, air movement reverses.
Q41. Why do sea breezes blow during day?
Ans: Land heats faster, air rises, cool air from sea fills gap.
Q42. Why are houses in hot regions painted white?
Ans: White reflects sunlight, reduces absorption.
Q43. Why does a black car heat up faster than a white car?
Ans: Black absorbs more radiation.
Q44. What is specific heat capacity?
Ans: Heat required to raise 1 kg substance by 1 K.
Q45. Why are metals used in cooking?
Ans: High conductivity transfers heat quickly.
Q46. Why are handles of kettles made of wood/plastic?
Ans: Poor conductors, safe to touch.
Q47. Define latent heat of fusion.
Ans: Heat required to change 1 kg solid to liquid without temperature change.
Q48. Define latent heat of vaporization.
Ans: Heat required to change 1 kg liquid to gas without temperature change.
Q49. Why does ice float on water?
Ans: Density of ice is less than water.
Q50. Why is water a good coolant?
Ans: High specific heat capacity.
Q51. Why do we feel cool after sweating?
Ans: Evaporation absorbs body heat.
Q52. Why do deserts have high temperature difference day & night?
Ans: Sand has low specific heat capacity.
Q53. Why is iron gate provided with gaps?
Ans: To allow expansion in summer.
Q54. Why are bridges provided with expansion joints?
Ans: To prevent damage due to thermal expansion.
Q55. Why are telegraph wires left loose?
Ans: To prevent snapping in winter due to contraction.
Q56. Why does a metal lid of glass jar open easily when heated?
Ans: Metal expands more, loosens grip.
Q57. Why does water boil faster in hills?
Ans: Low atmospheric pressure → lower boiling point.
Q58. Why are cooking vessels blackened from below?
Ans: To absorb more heat.
Q59. Why are refrigerators painted white inside?
Ans: To reflect heat, keep cool.
Q60. Define thermal expansion.
Ans: Increase in size of substance on heating.
Q61. Why is expansion in liquids used in thermometers?
Ans: Liquids expand uniformly with temperature.
Q62. Explain how thermos flask prevents heat loss.
Ans: Double walls (vacuum), silver coating, cork, reduces conduction, convection, radiation.
Q63. Why do we use pressure cookers?
Ans: High pressure raises boiling point, cooks faster.
Q64. Why do we shiver in cold?
Ans: Body tries to generate heat by muscular activity.
Q65. Why are engines cooled with water?
Ans: High specific heat absorbs heat.
Q66. Why is mercury used in thermometers?
Ans: Good conductor, expands uniformly, visible.
Q67. Why is alcohol used in very cold region thermometers?
Ans: Lower freezing point than mercury.
Q68. State two examples of heat transfer by convection in nature.
Ans: Winds, ocean currents.
Q69. Why is radiation important for Earth?
Ans: Transfers solar energy.
Q70. Why do we prefer cotton clothes in summer?
Ans: Absorb sweat, allow evaporation, keep cool.
Numerical Questions
Formulae to use:
Heat (Q) = m × c × ΔT
Latent heat (Q) = m × L
Q71. Find heat required to raise temp of 1 kg water from 20 °C to 100 °C. (c=4200 J/kgK)
Ans: Q=1×4200×(100-20)=3,36,000 J
Q72. 2 kg copper heated from 30 °C to 80 °C. c=390 J/kgK. Find heat.
Ans: Q=2×390×50=39,000 J
Q73. 500 g iron heated from 25 °C to 75 °C, c=450 J/kgK.
Ans: Q=0.5×450×50=11,250 J
Q74. 250 g water cooled from 80 °C to 20 °C. Find heat lost.
Ans: Q=0.25×4200×60=63,000 J
Q75. How much heat to convert 2 kg ice at 0 °C into water? (Lf=3.34×10⁵)
Ans: Q=2×3.34×10⁵=6.68×10⁵ J
Q76. Find heat to convert 1 kg water at 100 °C into steam. (Lv=2.26×10⁶)
Ans: Q=1×2.26×10⁶=2.26×10⁶ J
Q77. A 200 g aluminium block heated 30 °C → 90 °C, c=900 J/kgK.
Ans: Q=0.2×900×60=10,800 J
Q78. 1 kg lead, c=130 J/kgK, temp rise 40 °C. Heat?
Ans: Q=1×130×40=5,200 J
Q79. 0.5 kg mercury, c=140 J/kgK, ΔT=100 °C.
Ans: Q=0.5×140×100=7,000 J
Q80. Heat to raise 2 kg water by 10 °C.
Ans: Q=2×4200×10=84,000 J
Q81. 100 g copper, c=390, temp rise 70 °C. Heat?
Ans: 0.1×390×70=2,730 J
Q82. 3 kg aluminium, ΔT=50 °C, c=900. Heat?
Ans: 3×900×50=135,000 J
Q83. Convert 1 kg ice at 0 °C into steam at 100 °C. (c=4200, Lf=3.34×10⁵, Lv=2.26×10⁶)
Ans: Q=3.34×10⁵ + 4.2×10⁵ + 2.26×10⁶=3.02×10⁶ J
Q84. 2 kg water cooled 80 °C → 20 °C. Heat loss?
Ans: 2×4200×60=504,000 J
Q85. 0.5 kg iron, c=450, ΔT=100 °C.
Ans: 0.5×450×100=22,500 J
Q86. 1 kg water converted to ice at 0 °C. Heat lost?
Ans: 1×3.34×10⁵=3.34×10⁵ J
Q87. Raise 5 kg water from 25 °C to 75 °C.
Ans: 5×4200×50=10,50,000 J
Q88. 200 g aluminium, ΔT=40 °C. Heat?
Ans: 0.2×900×40=7,200 J
Q89. How much heat needed to melt 5 kg ice?
Ans: 5×3.34×10⁵=16.7×10⁵ J
Q90. Steam (1 kg) condensed at 100 °C. Heat released?
Ans: 1×2.26×10⁶=2.26×10⁶ J
Q91. 2 kg iron, ΔT=25 °C, c=450.
Ans: 2×450×25=22,500 J
Q92. 100 g water heated 20 °C → 100 °C.
Ans: 0.1×4200×80=33,600 J
Q93. 250 g ice melted. Heat absorbed?
Ans: 0.25×3.34×10⁵=83,500 J
Q94. 1 kg aluminium (c=900) cooled from 100 → 20 °C.
Ans: 1×900×80=72,000 J
Q95. 500 g water, ΔT=50 °C. Heat?
Ans: 0.5×4200×50=105,000 J
Q96. 10 g ice melted. Heat?
Ans: 0.01×3.34×10⁵=3,340 J
Q97. 100 g steam condensed. Heat released?
Ans: 0.1×2.26×10⁶=2.26×10⁵ J
Q98. Raise 0.2 kg copper from 25 to 125 °C, c=390.
Ans: 0.2×390×100=7,800 J
Q99. Water 2 kg heated 40 °C → 100 °C. Heat?
Ans: 2×4200×60=504,000 J
Q100. Find heat to melt 2 kg ice at 0 °C into water at 50 °C.
Ans: (2×3.34×10⁵) + (2×4200×50) = 6.68×10⁵ + 4.2×10⁵ = 10.88×10⁵ J