NCERT Solutions for Class 7 Science Curiosity Chapter 7

NCERT Solutions for Class 7 Science Curiosity Chapter 7  Heat Transfer in Nature are designed as per the latest CBSE syllabus to help students understand the various methods of heat transfer such as conduction, convection, and radiation. These solutions provide clear and step-by-step answers to all textbook questions, including intext and exercise questions. By following these solutions, students can strengthen their conceptual understanding and improve their performance in exams. 

NCERT Solutions for Class 7 Science Curiosity Chapter 7 Introduction 

In our daily life, we often feel heat around us  from the Sun, a hot cup of tea, or a burning candle. But have you ever wondered how this heat moves from one place to another? Chapter 7  Heat Transfer in Nature helps us understand the different ways heat travels – through solids, liquids, gases, and even empty space. This chapter explores the natural processes that allow heat to flow, keeping the Earth’s temperature balanced and affecting weather patterns, sea breezes, and even cooking!

Chapter Overview

This chapter focuses on three main types of heat transfer:

• Conduction – Heat transfer in solids.
  
  

• Convection – Heat transfer in liquids and gases.
  
  

• Radiation – Heat transfer without any medium.
  
  

Students will also learn:

• Why smoke rises upwards.
  
  

• How sea breeze and land breeze occur.
  
  

• Why water seeps underground.
  
  

• How the water cycle plays a role in maintaining Earth’s temperature.
  
  

Activities and experiments in this chapter make learning interactive and help students observe how heat behaves in different materials. This chapter is an essential part of the Class 7 Science syllabus and lays the foundation for understanding thermal processes in higher classes.

Class 7 Science Chapter 7 Heat Transfer in Nature Question Answer

Below are the solutions to all the questions from NCERT Class 7 Science Chapter 7  Heat Transfer in Nature.

Activity 7.1: Let us experiment Caution 

This activity should be carried out under the supervision of a teacher or an adult. Table 7.1: Falling of pins Reasons for what you observed Prediction Observation Pin falling fi rst  Take a strip of a metal, such as aluminium or iron, about 15 cm long. 

 Attach four pins to the strip with the help of wax such that they are arranged at nearly equal distances (about 2 cm apart), as shown in Fig. 7.1.  

Secure the strip to a stand and label the pins as I, II, III, and IV, as shown in Fig. 7.1. (If a stand is not available, place the strip between two bricks for support.)  

Heat the end of the strip that is away from the stand with a candle or a spirit lamp. Metal strip Burning candle Stand Pin Fig. 7.1: Heat transfer in a metal strip.

What will happen to the pins? Will they remain attached to the strip or will they fall?  Predict the order in which the pins will fall from the strip.  Record your observations in Table 7.1. 

Answer: 

Table 7.1: Falling of Pins

Conclusion: Heat is transferred from the hotter end of the metal strip to the cooler end by the process of conduction. This is why the pins fell in order from the nearest to farthest from the candle.

Activity 7.2: Let us investigate

 Take two identical paper cups.  Hang them using threads of equal length in an inverted position on the two ends of a wooden stick, as shown in Fig. 7.3a. Fig. 7.3(a):

 Initial set-up Thread Wooden stick Paper cup Heat Transfer in Nature 93  

Now, adjust the positions of the cups, so that the stick is horizontal.  

Place a burning candle below one of the cups (Fig. 7.3b).  Observe what happens to the cup.  Record your observations in Table 7.3 and think of probable reasons.

Answer:

Aim: To observe how hot air rises and affects the balance of the cups.

Steps:

1. Take two identical paper cups and hang them upside down from both ends of a wooden stick using equal-length threads.
   
   

2. Adjust them so the stick remains horizontal and balanced.
   
   

3. Place a burning candle below one of the cups.
   
   

4. Watch what happens to the cup above the candle.
   
   

Table 7.3: Recording Observations and Probable Reasons

Conclusion:

Smoke or hot air rises because it becomes lighter than the surrounding cool air. This upward movement of warm air is due to the process of convection.

Activity 7.3: Let us fi nd out Caution— This activity should be carried out under the supervision of a teacher or an adult. 

 Take a 500 mL beaker, half-fi lled with water as shown in Fig. 7.5a.  

With the help of a straw, place a grain of potassium permanganate at the centre of the beaker’s base (Fig. 7.5a).  

Place a candle right below the centre of the base of the beaker. 

 Observe the movement of the coloured streak in the water.  

As you supply heat, a streak of colour starts moving up and then coming down from the sides (Fig. 7.5b).

Answer: 

Aim:

To observe how heat is transferred in liquids and to understand if liquids rise when heated, similar to air.

Materials Needed:

• 500 mL beaker (half-filled with water)
  
  

• Potassium permanganate (or any food coloring)
  
  

• Straw
  
  

• Candle or burner
  
  

Procedure:

1. Take a 500 mL beaker and fill it halfway with water.
   
   

2. Using a straw, gently place a small grain of potassium permanganate at the center of the beaker’s base.
   
   

3. Place a burning candle directly below the center of the beaker.
   
   

4. Watch how the colored streak from the potassium permanganate moves in the water.
   
   

Observation:

As heat is supplied, the colored streak starts rising in the center and then moves downward along the sides of the beaker, forming a circular motion.

Reason:

When the water at the bottom center is heated, it becomes lighter and rises up. The cooler, denser water from the top sinks down along the sides to take its place. This movement sets up a convection current in the water.

Conclusion:

Heat is transferred in liquids by convection. Heated water rises, and cooler water sinks, causing a continuous circulation of water. This shows that liquids rise when heated, just like air.

Activity 7.4: Let us investigate Caution

This activity should be carried out on a clear, sunny day under the supervision of a teacher or an adult.  Take two identical bowls as shown in Fig. 7.6.  Fill one bowl halfway with soil and the other bowl halfway with water.  Fix a laboratory thermometer in each bowl as shown in Fig. 7.6. Make sure that the bulbs of the thermometer are immersed in soil and water, and do not touch the bottoms or the sides of the bowls.  Place the set-up in sunlight.

Answer:

Observations:

• No, the temperature did not rise by the same amount in both.
  
  

• The soil got heated faster than the water.
  
  

• After 20 minutes, for example:
  
  

• Rise in soil temperature: approx. 12°C
  
  

• Rise in water temperature: approx. 5°C

Answer: 

Table 7.5: Seepage of water

Conclusion:

The seepage rate depends on the particle size and pore space of the material.

• Gravel allows fast seepage,
  
  

• Sand allows moderate seepage,
  
  

• Clay allows very slow seepage.

InText Questions

Question 1: How does heat get transferred in cooking utensils made of metals?
Answer:
Heat is transferred in metal utensils by conduction. In this process, heat moves from the hot part of the metal to the cooler parts by passing energy from one particle to the next. The particles don’t move themselves, but they pass on the heat.

Question 2: Identify whether the given materials are good or poor conductors of heat.

Question 3: Why is the smoke going up?
Answer:
Smoke rises because it is hot. Hot air becomes lighter and moves upward. This movement is due to convection, where warm air rises above the cooler air around it, carrying the smoke upward.

Question 4: How does heat transfer take place in liquids? Do liquids also rise up when heated, like air?
Answer:
Yes, heat in liquids is transferred by convection. When the bottom part of a liquid gets heated, it becomes lighter and rises. The cooler liquid from the top comes down to replace it. This movement continues until the whole liquid is heated, just like air.

Question 5: How does the heat from the fire reach us?
Answer:
The heat from a fire reaches us through radiation. In radiation, heat travels in the form of waves and doesn’t need any medium like air or water to move. That’s why we can feel the heat even if we are not touching the fire.

Question 6: How does water seep through the surface of the Earth?
Answer:
Water goes into the ground through a process called infiltration. It passes through the spaces between soil particles like sand, gravel, or clay and gets stored deep underground in places called aquifers.

Let Us Enhance Our Learning

Question 1.
Choose the correct option in each case.
(i) Your father bought a saucepan made of two different materials, A and B, as shown in Fig. 7.14. The materials A and B have the following properties

(a) Both A and B are good conductors of heat
(b) Both A and B are poor conductors of heat
(c) A is a good conductor and B is a poor conductor of heat
(d) A is a poor conductor and B is a good conductor of heat

(ii) Pins are stuck to a metal strip with wax and a burning candle is kept below the rod, as shown in Fig. 7.15. Which of the
following will happen?
(a) All the pins will fall almost at the same time
(b) Pins I and II will fall earlier than pins III and IV
(c) Pins I and II will fall later than pins III and IV
(d) Pins II and III will fall almost at the same time

(iii) A smoke detector is a device that detects smoke and sounds an alarm. Suppose you are fitting a smoke detector in your room. The most suitable place for this device will be:
(a) Near the floor
(b) In the middle of a wall
(c) On the ceiling
(d) Anywhere in the room
Answer:
(i) (c) A is a good conductor and B is a poor conductor of heat
(ii) (d) Pins II and III will fall almost at the same time
(iii) (c) On the ceiling

Question 2. A shopkeeper serves you cold lassi in a tumbler. By chance, the tumbler had a small leak. You were given another tumbler by the shopkeeper to put the leaky tumbler in it. Will this arrangement help to keep the lassi cold for a longer time? Explain.
Answer:

Yes, this arrangement will help keep the lassi cold for a longer time. The air trapped between the two tumblers acts like an insulator because air does not allow heat to pass easily. This slows down the heat from entering the inner tumbler, so the lassi stays cooler for longer.

Question 3: State with reasons whether the following statements are True or False.

(i) Heat transfer takes place in solids through convection.
Answer: False
In solids, heat is transferred by conduction, not convection. The particles in solids are fixed and do not move from place to place.

(ii) Heat transfer through convection takes place by the actual movement of particles.
Answer: True
Yes, convection happens when particles move from the hotter area to the cooler area, carrying heat with them. This is common in liquids and gases.

(iii) Areas with clay materials allow more seepage of water than those with sandy materials.
Answer: False
Clay has very small particles and tiny spaces, so water seeps very slowly. Sandy and gravelly soils allow water to pass faster due to their larger spaces between particles.

(iv) The movement of cooler air from land to sea is called land breeze.
Answer: True
At night, the land cools faster than the sea. The cool air from the land moves towards the sea, and this movement is known as a land breeze.

Question 4: Some ice cubes placed in a dish melt into water after some time. Where do the ice cubes get heat for this transformation?

Answer:
The ice cubes absorb heat from their surroundings—like the air, the dish, and the surface they are kept on. This heat melts the ice, changing it from a solid to liquid (water).

Question 5: A burning incense stick is fixed, pointing downwards. In which direction would the smoke from the incense stick move? Show the movement of smoke with a diagram.

Answer:
The smoke will move upward. This is because the smoke is warm and mixed with hot air. Hot air becomes lighter and rises, so the smoke also moves upwards due to convection.

Question 6: Two test tubes with water are heated by a candle flame as shown in Fig. 7.16. Which thermometer (Fig. 7.16 a or Fig. 7.16 b) will record a higher temperature? Explain.

Answer:
The thermometer in Fig. 7.16 (a) will show a higher temperature.
In this setup, the bottom of the test tube is directly heated, and the thermometer is placed at the top. As water heats up at the bottom, it rises up through convection, carrying the heat to the thermometer at the top.
In Fig. 7.16 (b), the side of the test tube is heated, and the thermometer is at the bottom. This doesn’t heat the water effectively where the thermometer is placed.

So, convection works better in setup (a), and the temperature rises faster.

Question 7: Why are hollow bricks used to construct the outer walls of houses in hot regions?

Answer:
Hollow bricks trap air inside them, and air is a poor conductor of heat. This trapped air reduces the amount of heat entering the house. That’s why in hot areas, using hollow bricks helps to keep the house cooler from inside.

Question 8: Explain how large water bodies prevent extreme temperature in areas around them.

Answer:
Big water bodies like seas and oceans help to keep the nearby areas cooler in summer and warmer in winter.

• During the day, land gets heated faster than water. So, cooler air from the sea moves to the land. This is called a sea breeze, and it helps to keep the land cooler.
  
  

• At night, land cools down faster than the sea. Now, the cool air from the land moves to the sea, which is called a land breeze.
  
  

This movement of air controls the temperature and prevents it from becoming too hot or too cold in coastal areas.

Question 9: Explain how water seeps through the surface of the Earth and gets stored as groundwater.

Answer:
When it rains, water slowly goes into the ground through spaces between soil and rocks. This process is called infiltration.
The water fills up the tiny gaps and cracks in soil and rocks and gets stored under the ground. These storage areas are called aquifers, and the water stored in them is called groundwater.

Question 10: The water cycle helps in the redistribution and replenishment of water on the Earth. Justify the statement.

Answer:
The water cycle keeps moving water around the Earth.

• Water evaporates from rivers, lakes, and oceans due to the Sun’s heat.
  
  

• It condenses in the sky to form clouds.
  
  

• Then it falls as rain or snow (precipitation).
  
  

This rainwater goes into rivers, lakes, and underground layers, refilling them. So, the water cycle reuses and moves water to different places, making sure we have water all the time.

NCERT Solutions for Class 7 Science Curiosity Chapter 7 PDF Download

Students can download the NCERT Solutions for Class 7 Science Curiosity Chapter 7  Heat Transfer in Nature in PDF format from the link provided below. The PDF includes detailed answers to all in-text and exercise questions, making it easier for students to revise and understand the concepts of heat transfer through conduction, convection, and radiation. It is a helpful resource for exam preparation and quick revision.