Class 7 Science Chapter 9 – Transfer of Heat In Nature – All Textual Solutions | ASSEB Assam (English Medium)

Class 7 Science Chapter 9 Transfer of Heat In Nature Solutions | ASSEB Assam | English Medium

Class 7 Science (Amar Bijan) Chapter 9 – Transfer of Heat In Nature Complete Textual Question Answers and Solutions (ASSEB Assam – English Medium)

The ninth chapter of the Class 7 Science (English Medium) syllabus, ‘Transfer of Heat In Nature,’ is a practical and highly engaging topic in physics. Based on the new ASSEB (Assam State School Education Board) guidelines and the latest National Education Policy (NEP) framework according to the current syllabus, we have prepared comprehensive textual question answers for this chapter. This special guide includes very short answers (VSA), short questions, long descriptive answers, multiple-choice questions (MCQs), and additional questions. Brought to you by Ospin Academy, these solutions are accurate, easy to understand, and highly exam-oriented.

In ‘Transfer of Heat In Nature’, students explore how heat energy moves from one place to another through conduction, convection, and radiation. The chapter beautifully explains natural phenomena such as the sea breeze and land breeze, as well as the practical applications of conductors and insulators in everyday life (like cooking utensils and winter clothing). Understanding these concepts is vital for exam preparation. Our textual solutions not only cover the textbook exercises but also provide extra important questions and MCQs to ensure students have a thorough grasp of the topic.

What you will learn and get from these textual solutions:

• Clear definitions and differences between conduction, convection, and radiation.
• 1-mark objective questions (VSA), MCQs, and detailed 2-3 mark short questions tailored for exams.
• Step-by-step explanations for 4-5 mark long questions, including the mechanisms of sea breeze and land breeze.
• A wide range of additional questions and MCQs specifically designed according to the new syllabus pattern.
• Comprehensive insights into identifying good conductors and insulators of heat, explained in simple English.

Special Features of Ospin Academy’s Notes:

• Prepared strictly according to the new ASSEB syllabus and current educational guidelines.
• 100% accurate and written in simple, easy-to-memorize English (Class 7 Science Notes).
• Includes quick revision summaries of heat transfer modes, highly beneficial for last-minute exam preparation.
• Exclusive compilation of extra important questions and MCQs to maximize your scores.

Aiming for academic excellence, Ospin Academy provides these comprehensive textual solutions to aid students in their studies. Start your preparation today and secure the highest marks in Class 7 Science.

 SCERT Assam, Class 7: Science

Lesson-9                                                                 Ospin Academy

Transfer of Heat In Nature

 

EXERCISE 

1. State whether True or False.
(a) In solids, heat is transferred mainly through the process of convection. [T/F]
Answer: False

 (b) Air gets heated by the process of convection. [T/F]
Answer: True 

(c) Radiation is a method of heat transfer that requires a medium. [T/F]
Answer: False 

(d) Water seeps through clay faster than through gravel. [T/F]
Answer: False 

(e) A sea breeze is the movement of cooler air from the sea towards the land during the day. [T/F]
Answer: True 

2. Darken the circle of the correct answer
(i) A hot metal pan is removed from a flame and placed on a pan counter. It eventually cools down to room temperature. How does it primarily lose its heat?
(a) Through convection.
(b) Through conduction.
(c) Through radiation.
(d) Through a combination of conduction and convection.
Answer: (c)

(ii) What is the primary reason why water seeps much more slowly through clay than through gravel?
(a) Clay is found deeper underground than gravel.
(b) Gravel particles are smaller and remain packed together more tightly.
(c) The spaces between clay particles are much smaller and loosely bound.
(d) The chemical composition of clay repels water.
Answer: (c)

(iii) Which of the following processes primarily transfer heat through a solid metal rod and water?
(a) Radiation and convection
(b) Conduction and convection
(c) Convection and radiation
(d) Radiation and conduction
Answer: (b)

(iv) A pressure cooker is made of steel or aluminium, while its handle is made of plastic or wood. Why are different materials used?
(a) Steel or aluminium is a poor conductor of heat, and plastic is a good conductor.
(b) Steel or aluminium is a good conductor of heat, and plastic is a poor conductor.
(c) Steel or aluminium transfers heat by convection, while plastic transfers heat by conduction.
(d) Steel or aluminium transfers heat by conduction, while plastic transfers heat by convection.
Answer: (b)

3. Read the following two statements carefully. One of them is
given as the ‘Assertion’ and the other as the ‘Reason’.
Assertion: Sea breeze blows from the sea toward the land during day
time.
Reason: Land gets heated up faster than water under sunlight, so
warm air over land rises and is replaced by cooler air from the sea.
Choose the correct answer from the available options
(a) Both Assertion and Reason are true, and Reason is the correct
explanation of Assertion.

(b) Both Assertion and Reason are true, but Reason is not the correct
explanation of Assertion.
(c) Assertion is true, but Reason is false.
(d) Assertion is false, but Reason is true.
Answer: (a)

4. Fill up the blanks
(a) The process of heat transfer from the hotter part of an object to a colder part without changing the position of its particles is called __________.
Answer: conduction 

(b) Materials that do not allow heat to pass through them easily are called __________ of heat.
Answer: poor conductor / insulator 

(c) In liquids and gases, heat is transferred mainly by the process of __________.
Answer: convection 

(d) All kind of objects exchange heat with their surroundings through the process of __________.
Answer: radiation

5. A stainless-steel spoon kept in a cup of hot water becomes hot w ithin a few minutes. Explain how heat is transferred along the spoon and predict which part becomes hot first and which part gets heated up last?
Answer: Heat is transferred along the solid stainless-steel spoon through the process of conduction. Since steel is a good conductor of heat, the heat energy travels from particle to particle without the particles themselves moving.
The part of the spoon that is submerged and in direct contact with the hot water becomes hot first. The heat then travels up the handle, so the part of the spoon furthest from the water (the tip of the handle) gets heated up last.

6. Draw a labelled diagram of evaporation, condensation, precipitation, and infiltration to show the continuous movement of water through the environment.
Answer: 

7. On sunny days in coastal areas, houses often have windows open facing towards the sea. Explain how this design helps keep the indoors comfortable, with reference to the mechanism of sea breeze.
Answer: During sunny days, the land heats up much faster than the sea water. Consequently, the air directly above the land becomes hot, expands, and rises up. To fill this resulting low-pressure area, the cooler, denser air from above the sea continuously rushes towards the land. This refreshing flow of cool air is called a sea breeze.
By keeping windows facing the sea open, the houses allow this constant, natural cool sea breeze to enter directly. This effectively replaces the warm indoor air, naturally cooling the house and keeping the indoors very comfortable during the hot day.
8. People sitting around a fireplace feel warm even if the air between them is cool. Explain the actual mode of heat transfer involved in this process.
Answer: The primary mode of heat transfer involved here is radiation. Unlike conduction or convection, thermal radiation does not require any physical medium (like solid, liquid, or gas) to travel. The heat energy from the fire travels directly outward in the form of electromagnetic waves. When these invisible heat waves strike the people sitting around, their bodies absorb the energy and they feel warm, completely bypassing the cold air between them.

9. List the major causes of groundwater depletion, highlighting the specific factors in rural, urban, and industrial areas.
Answer:
(a) Causes of groundwater depletion in rural areas
(i) Extensive cultivation of high water-demanding crops (like paddy).
(ii) Severe wastage of water due to inefficient, unscientific irrigation systems. 

(b) Causes of groundwater depletion in urban areas
(i) Massive over-extraction of groundwater via borewells by a rapidly growing population for daily needs.
(ii) Extensive concrete paving and asphalt roads completely block the natural infiltration of rainwater into the ground. 

(c) Causes of groundwater depletion in industrial areas
(i) Unregulated and excessive pumping of huge volumes of groundwater for use in manufacturing processes.
(ii) Severe pollution of existing groundwater tables by toxic industrial effluents and chemical discharge. 

10. Two identical cups are filled with equally hot tea—one porcelain and one stainless steel. Predict which cup of tea will remain hot for a longer time, and explain the reason.
Answer: The tea in the porcelain cup will remain hot for a considerably longer time.
This happens because porcelain is a poor conductor of heat (an insulator). It severely restricts the flow of thermal energy from the hot tea to the outside environment, trapping the heat inside the cup.
Conversely, stainless steel is a very good conductor of heat. It rapidly draws the heat away from the tea and transfers it to the outer surface of the cup, where it is quickly lost to the surrounding air via radiation and convection, causing the tea to cool down much faster.
11. The temperatures of three substances were recorded after being heated to the same temperature and then allowed to cool under the same conditions. The data are shown below: 

Sl. No	Time (minutes)	Temperature of Substance A (°C)	Temperature of Substance B (°C)	Temperature of Substance C(°C)
1.	0	80	80	80
2.	10	72	65	55
3.	20	66	58	40
4.	40	62	46	32

Answer the following :
(a) Which substance cools fastest?
Answer: Substance C 

(b) Which substance retains heat for the longest time?
Answer: Substance A 

(c) Based on the above data, which substance would you prefer to use for making a tea cup?
Answer: Substance A 

12. A hot water bag gradually cools down after being used for some time. Through which process does it lose heat? Explain.
Answer: A hot water bag loses heat through all three modes of heat transfer, but primarily through conduction and radiation.
First, the heat from the hot water is transferred to the inner surface of the rubber bag via conduction (since they are in direct contact). The heat then conducts through the thickness of the rubber material to its outer surface. When placed against a patient’s body, the heat is again transferred from the outer surface of the bag directly to the skin via conduction.
Additionally, the exposed outer surface of the hot bag continuously loses heat to the surrounding cooler room air through thermal radiation and convection.
13. Explain why do thin blankets used together provide more warmth in winter than a single thick blanket?
Answer: Using two thin blankets together is warmer because a distinct layer of air gets trapped between the two blankets. Air is a very poor conductor of heat (an excellent insulator). This trapped air layer acts as a highly effective insulating barrier that prevents the body heat from escaping into the cold surrounding environment. A single thick blanket does not have this extra insulating layer of trapped air, thus allowing more body heat to escape.

14. Why is it advised to paint the outer walls of buildings white in hot regions?
Answer: It is strongly advised to paint outer walls white in hot regions because the color white is an excellent reflector and a very poor absorber of thermal radiation. When intense sunlight hits a white wall, it reflects the vast majority of the radiant heat energy back into the atmosphere rather than absorbing it. This significantly prevents the walls from heating up, thereby keeping the inside of the building naturally much cooler and more comfortable during scorching summers.

MCQ( Multiple Choice Question)

1. What is the mode of heat transfer that does not require any medium?
(A) Conduction
(B)  Convection
(C) Radiation
(D) Infiltration
Answer: (C) Radiatio

2. Which of the following is a good conductor of heat?
(A)  Wood
(B) Plastic
(C) Aluminium
(D)  Rubber
Answer: (C) Aluminium

3. In substances like air and water, heat is primarily transferred by which process?
(A)  Conduction
(B)  Convection
(C) Radiation
(D)  Condensation
Answer: (B) Convection

4. How does heat travel along a hot metal rod?
(A)  Convection
(B)  Radiation
(C)  Conduction
(D)  Infiltration
Answer: (C)  Conduction

5.  Why does painting outer walls white help keep a house cooler?
(A) White absorbs more heat
(B) White reflects heat
(C) White increases airflow
(D) White generates heat
Answer: (B) White reflects heat

6. Why do two thin blankets together provide more warmth than one thick blanket?
(A) They are heavier
(B) Trapped air insulates
(C) Thin blankets produce heat
(D) Thick blankets expel air
Answer: (B) Trapped air insulates

7. A hot-water bottle cools down mainly by which combination?
(A) Only conduction
(B) Only radiation
(C) Conduction, radiation and convection
(D) Only convection
Answer: (C) Conduction, radiation and convection

8. Why does cool air flow from the sea toward land during daytime at the coast?
(A) Sea heats faster than land
(B) Land heats faster than sea
(C) Land is always cooler
(D) Sea produces heat
Answer: (B) Land heats faster than sea

9. Which process allows rainwater to seep into the ground easily?
(A) Radiation
(B) Infiltration
(C)  Convection
(D) Condensation
Answer: (B) Infiltration

10. Why does tea in a steel cup cool faster than in a porcelain cup?
(A) Steel is a good conductor
(B) Porcelain is a good conductor
(C) Steel does not radiate heat
(D) Porcelain loses heat quickly
Answer: (A) Steel is a good conductor

11. Which urban factor reduces groundwater recharge?
(A) More trees
(B) Concrete surfaces and pavements
(C) Heavy rainfall
(D) Waterless crops
Answer: (B) Concrete surfaces and pavements

12. Why do people feel warm near a fire even if the air is cool?
(A) Due to conduction
(B) Due to convection
(C) Due to radiation
(D) Due to infiltration
Answer: (C) Due to radiation

13. How does water mostly move slowly through soil?
(A) By radiation
(B)  By condensation
(C) By infiltration and percolation
(D) By convection
Answer: (C) By infiltration and percolation

14. Why is the handle of a pressure cooker usually made of plastic or wood?
(A) Because it is a good conductor
(B) Because it is a poor conductor
(C)  Because it melts easily
(D) ইBecause it generates heat
Answer: (B)  Because it is a poor conductor

15.  What is the process by which water vapor forms clouds?
(A) Evaporation
(B)  Condensation
(C) Infiltration
(D)  Convection
Answer: (B) Condensation

16. Which soil property most affects the speed of water seepage?
(A) Color
(B) Particle size and pore spaces
(C) Depth of roots
(D) Smell
Answer: (B) Particle size and pore spaces

17. Why is wearing dark-coloured clothes useful in cold weather?
(A) They let heat escape
(B) They absorb heat more
(C) They increase airflow
(D) They store water
Answer: (B) They absorb heat more

18. What likely happens when groundwater is over-extracted for agriculture?
(A) Groundwater increases
(B) Water table lowers
(C) More rainfall occurs
(D) Soil becomes more fertile
Answer: (B) Water table lowers

19. How does a fan cool the body?
(A) By adding heat
(B) By increasing sweat evaporation
(C) By absorbing air heat
(D) By stopping radiation
Answer: (B) By increasing sweat evaporation

20. Heat always flows from:
(A) Cold to hot
(B) Hot to cold
(C) Between same temperature bodies
(D) Only by emitting heat
Answer: (B) Hot to cold

B. 15 Long Questions and Answers

1.  Briefly explain the difference between conduction, convection and radiation.
Answer: Conduction transfers heat through solids by particle-to-particle contact without particle movement. Convection transfers heat in liquids and gases via bulk movement of fluid. Radiation transfers heat through electromagnetic waves and needs no medium.

2. Describe how heat travels along a steel spoon placed in hot water and which part heats first/last.
Answer: Heat moves by conduction along the metal; the submerged end heats first and the far end of the handle last.

3. List stages of the water cycle and give one example of each.
Answer: Evaporation (water evaporates — pond evaporation), Condensation (cloud formation), Precipitation (rainfall), Infiltration/percolation (rainwater soaking into soil).

4.  Explain how sea breeze forms in coastal areas in daytime and give an example.
Answer: Land warms faster than sea, causing rising warm air over land and a pressure difference that draws cooler sea air inland; e.g., opening windows toward the sea lets the sea breeze cool homes.

5. Name three main causes of groundwater depletion with examples for rural and urban areas.
Answer: Over-extraction (e.g., intensive irrigation in villages; borewell pumping in cities), blocked infiltration (urban concrete cover), and pollution from industrial effluents.

6. Why does tea stay hot longer in a porcelain cup? Explain briefly.
Answer: Porcelain is an insulating material (poor conductor), so it slows heat loss and keeps tea hot longer.

7.  How do two thin blankets together conserve heat better? Describe.
Answer: The trapped air layer between blankets acts as insulation (poor conductor), reducing heat loss from the body.

8. State the scientific reason coastal homes keep windows facing the sea open on hot days.
Answer: Opening sea-facing windows allows natural sea breeze (cooler air moving inland) to replace warm indoor air, cooling the house.

9.  Give three characteristics of thermal radiation.
Answer: No medium required; travels in straight lines and in all directions; surface colour/finish affects absorption and reflection.

10. What are harmful effects of excessive digging of borewells?
Answer: Lowered water table, risk of salinization, increased pumping costs, and reduced water availability for agriculture.
11: From a heat-conservation viewpoint, why should drafts under doors or windows be blocked in cold weather?
Answer: Blocking drafts prevents cold air entry that increases heat loss, thereby conserving indoor warmth and reducing heating needs.
12: How is land breeze formed at night? Give a short explanation.
Answer: At night, land cools faster than sea, so cooler dense air flows from land to sea, producing land breeze.

13. Give an example and brief description illustrating condensation and precipitation.
Answer: Condensation—water vapour cools into tiny droplets forming clouds; Precipitation—cloud droplets coalesce, grow heavy and fall as rain.

14. List three simple household or community methods to conserve groundwater.
Answer: Rainwater harvesting, maintaining permeable ground surfaces to