Heat Transfer in Nature – MCQs with Answers and Explanations
Class 7
Science
Chapter 7
Heat Transfer in Nature — 40 MCQs with Answers & Explanations
Topic-wise MCQs covering conduction, convection, radiation and natural applications. Prepared strictly as per NCERT syllabus for CBSE Class 7.
Conduction — Questions 1–10
1. Which of the following is a good conductor of heat?
Answer: C. Copper. Metals like copper have free electrons that transfer thermal energy quickly, making them excellent conductors.
2. Conduction requires which condition?
Answer: B. Direct contact. Conduction occurs via particle-to-particle interactions when objects or parts of a body touch each other.
3. A metal rod heated at one end warms the other end by:
Answer: C. Conduction. Heat travels through the rod as particles pass energy along; metals conduct heat well due to free electrons.
4. Which will reduce heat conduction through a wall?
Answer: B. Add insulating material. Insulators have low thermal conductivity and slow heat transfer by conduction.
5. Which factor does NOT affect conduction?
Answer: B. Colour of material. Colour affects radiation but does not directly change thermal conductivity governing conduction.
6. Why do metal spoons have a hotter handle faster than wooden spoons?
Answer: B. Metal conducts heat faster. Metals transfer heat along their length quickly due to free electrons; wood is a poor conductor.
7. Which design change reduces conduction from a hot pan to its handle?
Answer: B. Use wooden or plastic grip. Insulating grips reduce heat conduction to hands, keeping the handle cooler.
8. Heat conduction is slowest in which state of matter?
Answer: C. Gases. In gases particles are far apart, so collisions are less frequent and conduction is less efficient compared to solids.
9. Which everyday object reduces conduction of heat between two surfaces?
Answer: B. Wooden cutting board. Wood is an insulator and reduces heat transfer by conduction between the hot object and tabletop.
10. Conduction cannot occur through:
Answer: D. Vacuum. Conduction needs particles to transfer energy; vacuum has none, so conduction cannot occur.
Convection — Questions 11–22
11. Convection is the main mode of heat transfer in:
Answer: B. Liquids and gases. Convection requires bulk fluid motion, so it occurs in liquids and gases where parts of the fluid can move.
12. Sea breeze occurs because:
Answer: B. Land heats faster than sea. Differential heating causes warm air over land to rise and cooler air from sea flows in, creating sea breeze (a convective circulation).
13. Which increases convection in a liquid?
Answer: B. Increasing temperature difference. Larger temperature differences create stronger buoyancy forces and faster convective flows.
14. Boiling water circulates due to:
Answer: C. Convection. Heated water becomes less dense and rises, while cooler water sinks, creating convective circulation.
15. Forced convection is produced by:
Answer: A. Fans or pumps. External devices move fluid, enhancing convective heat transfer (forced convection).
16. Which example shows natural convection?
Answer: B. Water boiling without stirring. Boiling produces convective currents naturally due to temperature-driven density differences.
17. Which statement about convection is true?
Answer: B. It transfers heat by moving masses of fluid. Convection relies on bulk movement of fluid driven by temperature and density differences.
18. Which weather phenomenon is caused by convection?
Answer: B. Cloud formation. Warm moist air rises by convection, cools and condenses to form clouds, a key convective process in weather.
19. In which case is convection least significant?
Answer: B. Heat transfer through a metal rod. That's conduction; convection requires fluid motion so it's not significant in solid rods.
20. Which of these increases natural convection?
Answer: C. Increasing temperature differences. Greater temperature gradients strengthen buoyant forces and drive stronger convective currents.
Radiation — Questions 23–32
21. Which mode of heat transfer does not require a medium?
Answer: C. Radiation. Radiation travels by electromagnetic waves and can move through vacuum, unlike conduction or convection.
22. Why do dark surfaces become hotter in sunlight?
Answer: B. They absorb more radiation. Dark colours absorb more incoming solar radiation and convert it to heat, increasing temperature.
23. Which surface reflects most solar radiation?
Answer: B. Shiny metallic. Shiny metallic surfaces reflect a large fraction of incident light and radiation, reducing absorption.
24. The warmth we feel from sunlight on a cool day is due to:
Answer: C. Radiation. Sunlight reaches us as electromagnetic radiation and is absorbed by skin/clothes, producing warmth.
25. Which property determines how well a surface emits thermal radiation?
Answer: A. Emissivity. Emissivity measures how effectively a surface emits thermal radiation; high emissivity means better emission.
26. Shiny foil inside a thermos reduces heat loss mainly by reducing:
Answer: C. Radiation. Reflective inner surfaces bounce back emitted thermal radiation, reducing net radiative heat loss.
27. Which choice best explains why white roofs keep buildings cooler?
Answer: B. White reflects more solar radiation. Higher reflectivity (albedo) means less absorption of sunlight and lower heat gain.
28. Radiation from the Sun reaches Earth mainly as:
Answer: B. Electromagnetic waves. Solar energy travels through space as electromagnetic radiation including visible light and infrared.
29. Which action will most reduce radiative heat gain through a window?
Answer: B. Using reflective film or blinds. Reflective films and blinds reduce the amount of solar radiation entering, thus lowering radiative heat gain.
30. Which statement is true about radiation?
Answer: C. It can transfer heat through vacuum. Radiation travels as electromagnetic waves and doesn't need particles to propagate.
Applications & Natural Phenomena — Questions 31–40
31. Which process in the water cycle directly uses solar radiation?
Answer: B. Evaporation. Solar radiation supplies energy for liquid water to change into vapour, starting the water cycle.
32. Groundwater temperature is mainly influenced by:
Answer: B. Long-term conductive heat penetration. Heat slowly conducts from the surface into the ground, affecting groundwater over longer timescales.
33. Which factor helps coastal areas have milder climates?
Answer: B. Sea's high heat capacity and mixing. Oceans store and redistribute heat through convection and mixing, moderating coastal temperatures.
34. Why do deserts cool rapidly at night?
Answer: B. Low moisture and little vegetation lead to rapid radiative cooling. With little water or vegetation to store heat, deserts lose heat quickly after sunset by radiation.
35. Which practice reduces urban heat island effect?
Answer: B. Adding green roofs and reflective surfaces. Vegetation and reflective materials reduce heat absorption and increase cooling through shade and evapotranspiration.
36. Evaporation cools surfaces because it:
Answer: B. Absorbs latent heat. Energy is used to change liquid to vapour, taking heat from the surface and causing cooling.
37. Which measure helps reduce heat transfer into a building in hot climates?
Answer: B. Light-reflective roofing and insulation. Reflective surfaces reduce radiative gain and insulation slows conductive heat flow into buildings.
38. Why do lakes freeze from the top down?
Answer: B. Water is densest at 4°C and colder water stays on top. Colder water floats and freezes at the surface; ice insulates deeper water, protecting aquatic life.
39. Which factor least affects groundwater temperature?
Answer: C. Daily wind speed. Wind affects surface conditions more; groundwater changes slowly and depends on soil properties, depth and vegetation.
40. Best one-line summary of the chapter?
Answer: C. Heat moves by conduction, convection and radiation shaping natural processes. This captures the three modes and their role in phenomena like the water cycle and groundwater behaviour.