Heat Transfer in Nature – Short Answer Type Questions
Class 7
Science
Chapter 7
Heat Transfer in Nature — 50 Short Answer Questions (NCERT-aligned)
These short answer questions and answers follow the NCERT syllabus and are ideal for CBSE Class 7 board exam revision.
Overview: This set contains 50 topic-wise short-answer questions covering conduction, convection, radiation, and their roles in natural processes like the water cycle and groundwater movement. Answers are concise but explanatory — perfect for classroom revision and board preparation.
1. What is heat and how is it different from temperature?
Heat is a form of energy transferred between bodies due to temperature difference. Temperature measures the average kinetic energy of particles and indicates how hot or cold a body is.
2. Explain conduction with an example.
Conduction is heat transfer through direct contact; particles transfer energy by collisions. Example: A metal rod heated at one end becomes hot at the other end as heat conducts along the rod.
3. Explain convection with an example.
Convection is heat transfer by the bulk movement of fluid caused by density differences. Example: Warm air rising from heated land causes sea breeze as cooler air moves in to replace it.
4. Explain radiation and its significance in nature.
Radiation is heat transfer by electromagnetic waves; it can travel through vacuum. The Sun’s radiation heats Earth’s surface, driving weather patterns and the water cycle.
5. Why are metals good conductors of heat?
Metals have free electrons that transfer kinetic energy rapidly between atoms, making them efficient conductors of heat.
6. What makes a material an insulator?
Insulators have low thermal conductivity and often trap air pockets, slowing down heat transfer. Examples include wood, wool, and plastic.
7. How does radiation differ from conduction and convection?
Radiation does not require a medium and transfers energy via electromagnetic waves; conduction requires contact and convection requires fluid motion.
8. Give an example where all three modes of heat transfer act together.
Sunlight (radiation) heats the ground; heat conducts into soil layers and warms the air above, producing convection currents that carry warm air upward.
9. What is thermal equilibrium?
Thermal equilibrium occurs when two bodies in contact reach the same temperature and no net heat flows between them.
10. How does surface colour affect heating by radiation?
Dark and matte surfaces absorb more radiation and heat more quickly than light or shiny surfaces, which reflect more radiation.
11. Describe an experiment to show conduction.
Place a metal rod with wax pieces fixed along its length and heat one end; the wax melts progressively, showing heat conduction along the rod.
12. Describe a simple demonstration of convection.
Heat water in a beaker and add coloured dye; observe dye rising in warm areas and sinking in cool areas, visualising convection currents.
13. Why can radiation travel through empty space?
Radiation is electromagnetic waves that do not require particles to travel—hence they can propagate through a vacuum like space.
14. How does conduction affect groundwater temperature?
Heat from the surface conducts into deeper soil and rocks, slowly influencing the temperature of groundwater through thermal conduction.
15. Explain the role of solar radiation in the water cycle.
Solar radiation provides energy for evaporation of water from oceans and land, starting the water cycle which leads to condensation and precipitation.
16. What is forced convection? Give an example.
Forced convection occurs when an external force like a fan or pump moves fluid to transfer heat; e.g., a fan cooling a room by moving air.
17. How do thermos flasks reduce heat loss?
Thermos flasks use vacuum between walls to reduce conduction and convection; reflective inner surfaces reduce radiation loss, keeping contents hot or cold longer.
18. Why do coastal areas have milder climates?
Large water bodies moderate temperature because water has high heat capacity and oceanic convection distributes heat, reducing temperature extremes on coasts.
19. How do buildings use insulation to stay warm?
Insulation materials reduce conduction through walls and roofs and trap air to limit heat loss; double-glazed windows reduce radiation and conduction losses.
20. Explain how sea breeze forms during the day.
Land heats up faster than sea; warm air over land rises (convection) and cooler air from the sea moves in to replace it, creating a sea breeze.
21. Explain land breeze at night.
At night land cools faster than sea; air over sea is warmer and rises, causing cooler air from land to flow toward the sea as land breeze.
22. Why do shiny surfaces feel cooler in sunlight?
Shiny surfaces reflect more incident radiation and absorb less, so they remain cooler compared to dark, matte surfaces.
23. What is latent heat and its role in evaporation?
Latent heat is energy absorbed during a change of state without temperature change. During evaporation, latent heat is absorbed, cooling the surface.
24. How does wind affect heat distribution?
Winds transport warm and cold air masses, aiding convective heat transfer and influencing regional temperature and weather patterns.
25. Why are deserts cooler at night?
Deserts have little moisture and vegetation, so radiation loss at night is high and there is little to retain heat, causing rapid cooling.
26. How can painting roofs white reduce heat gain?
White paint reflects a large portion of solar radiation, reducing heat absorbed by the roof and cooling the building beneath.
27. What is the significance of specific heat capacity?
Specific heat capacity indicates how much heat energy is needed to change a material's temperature. Substances with high specific heat (like water) heat up slowly and retain heat longer.
28. Why do metals feel hotter than wood when heated?
Metals conduct heat quickly, transferring energy to your hand faster than wood, making metal feel hotter when heated.
29. How does convection contribute to cloud formation?
Warm moist air rises by convection, cools at higher altitudes, and the water vapour condenses into cloud droplets leading to cloud formation.
30. Explain how ocean currents redistribute heat globally.
Ocean currents driven by wind, temperature and salinity differences move warm water to cooler regions and vice versa, redistributing heat and affecting climate.
31. What determines the rate of heat conduction?
Rate of conduction depends on material's thermal conductivity, temperature difference, cross-sectional area, and thickness of the material.
32. How do animals use insulation?
Animals use fur, feathers or fat layers as insulation to trap air and reduce heat loss, helping maintain body temperature.
33. Why is evaporation from skin cooling?
Evaporation requires latent heat which is taken from the skin, removing heat and producing a cooling effect.
34. How does soil moisture affect heat transfer in soil?
Wet soil conducts heat differently from dry soil; moisture increases thermal conductivity but also affects heat capacity and evaporation cooling.
35. Describe an example of forced convection in daily life.
A heater with a fan distributing warm air in a room uses forced convection to spread heat evenly.
36. What is radiation balance of Earth (brief)?
Earth receives solar radiation and emits thermal radiation back to space; the balance between incoming and outgoing radiation affects global temperatures.
37. Why do some materials feel better to touch in winter?
Materials with low thermal conductivity (like wood or fabric) feel warmer to the touch in winter because they do not draw heat rapidly from your skin.
38. How do greenhouses trap heat?
Glass allows solar radiation in and traps long-wave radiation emitted by warm surfaces, reducing convective heat loss and keeping the interior warmer.
39. Explain how sunlight heats the ground differently than air.
Sunlight (radiation) is absorbed strongly by ground surfaces which heat up; air heats mainly by convection from the warmed ground rather than direct absorption.
40. How does altitude affect temperature and heat transfer?
Higher altitudes have lower air pressure and density, generally causing lower temperatures; thinner air changes convective heat transfer efficiency.
41. Why is water used for cooling engines?
Water has high specific heat and can absorb large amounts of heat, making it effective for removing heat from engines via convection and conduction.
42. How does humidity influence heat perception?
High humidity reduces evaporation of sweat, making it harder to lose heat and increasing perceived temperature (heat index).
43. What simple household step reduces heat gain through windows?
Using curtains or reflective blinds reduces solar radiation entering through windows and lowers heat gain.
44. Why does a black t-shirt feel hotter in sunlight?
Black absorbs more solar radiation, converting it into heat, so a black t-shirt warms the body more quickly than a light-coloured one.
45. How do glaciers influence regional climate?
Glaciers have high reflectivity (albedo) and reflect solar radiation, keeping regions cooler and influencing local heat balance.
46. What is the role of particulate matter in atmospheric heating?
Aerosols and dust can absorb or reflect radiation, affecting how much solar energy reaches the surface and thus influencing heating.
47. How do engineers reduce heat transfer in buildings?
Engineers use insulation, reflective surfaces, ventilated spaces, and efficient window designs to minimise unwanted heat transfer.
48. Explain why heat transfer is important to study.
Understanding heat transfer explains natural processes (weather, water cycle), helps design efficient buildings and devices, and solves problems of heating/cooling.
49. Give a brief method to measure which surface gets hotter in sun.
Place identical plates with different surface colours in sunlight and measure temperature after a fixed time; darker plates usually record higher temperatures.
50. In one short sentence, summarise the chapter's key idea.
Heat moves by conduction, convection and radiation, and these mechanisms explain many natural phenomena like the water cycle and temperature changes in Earth systems.
Note: Answers are concise yet explanatory for focused revision. All content is strictly aligned with the NCERT syllabus for CBSE Class 7.