RBSE Solutions Class 7 Science Chapter 7 Heat Transfer in Nature

Heat Transfer in Nature Class 7 Question Answer

RBSE Class 7 Science Chapter 7 Heat Transfer in Nature Question Answer

Class 7 Science Curiosity Chapter 7 Question Answer (Exercise)

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Question 1. Choose the correct option in each case,
(i) Your father brought a saucepan made of two different materials, A and B, as shown in Fig. 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
Answer: (c) A is a good conductor and B is a poor conductor of heat
In simple words: The main part of a saucepan that touches the heat needs to be a good conductor (material A) so food cooks fast. The handle (material B) should be a poor conductor to protect your hands from the heat.

🎯 Exam Tip: Remember that heat conductors allow heat to pass easily, while insulators (poor conductors) resist heat flow. This principle is key for understanding cooking utensils.

Question 1. (ii) Pins are struck to a metal strip with wax and a burning candle is kept below the rod, as shown in Fig. 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 fell later than pins III and IV
(d) Pins II and III will fell almost at the same time
Answer: (d) Pins II and III will fell almost at the same time
In simple words: When the candle heats the metal strip in the middle, the heat spreads outwards. Since pins II and III are closest to the heat source at the center, the wax holding them will melt almost at the same time, causing them to fall first.

🎯 Exam Tip: This setup demonstrates heat conduction. Heat travels from the warmest part to cooler parts. The pins closest to the flame will fall earliest as the wax melts due to conducted heat.

Question 1. (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: (c) On the ceiling
In simple words: Smoke from a fire is hot. Hot air and smoke rise upwards. So, a smoke detector placed on the ceiling will detect smoke earliest and sound the alarm quickly.

🎯 Exam Tip: Always place smoke detectors high up, ideally on the ceiling, as smoke naturally rises with hot air due to convection currents. This ensures early detection and safety.

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 to keep the lassi cold for a longer time. An air layer will form between the two tumblers. This layer of air is a poor conductor of heat, which means it slows down the transfer of heat from the outside warmer air to the cold lassi. Because air acts as an insulator, less heat reaches the lassi, allowing it to stay cold for a longer period.
In simple words: Yes, putting one tumbler inside another with air in between keeps the lassi cold longer. The air trapped between the two glasses acts like a shield, stopping heat from getting in easily.

🎯 Exam Tip: When materials like air are trapped, they act as insulators. This principle is used in double-walled containers like thermoses to keep things hot or cold for longer.

Question 3. State with reason(s) whether the following statements are True [T] or False [F].
(i) Heat transfer takes place in solids through convection.
Answer: False: Heat transfer in solids happens mainly through conduction. In conduction, heat moves as particles vibrate and pass energy to their neighbors without moving from their positions. Convection, which involves the actual movement of particles, is typical for liquids and gases.
In simple words: False. Solids move heat by conduction, where particles jiggle and pass energy. Convection happens in liquids and gases where particles themselves move to carry heat.

🎯 Exam Tip: Differentiate between conduction, convection, and radiation. Conduction involves direct contact, convection involves fluid movement, and radiation involves electromagnetic waves.

Question 3. (ii) Heat transfer through convection takes place by the actual movement of particles.
Answer: True: In convection, heat transfer occurs because the particles themselves move from one place to another, carrying thermal energy with them. This is common in fluids like liquids and gases where warmer, less dense parts rise and cooler, denser parts sink, creating a current. This constant motion is what allows heat to spread.
In simple words: True. Convection moves heat when the particles of a liquid or gas actually move, carrying heat with them. Warm particles rise, and cool particles fall.

🎯 Exam Tip: Convection currents are crucial for understanding weather patterns and how heating and cooling systems work in homes.

Question 3. (iii) Areas with clay materials allow more seepage of water than those with sandy materials.
Answer: False: Seepage is greater in sandy materials compared to clay materials. Sandy soils have larger spaces between their particles, which allows water to flow through them more easily and quickly. Clay particles are much smaller and packed more tightly, reducing the spaces and making water seepage slower.
In simple words: False. Sand lets water seep through faster than clay. Sand has bigger gaps between its grains, so water can pass through easily.

🎯 Exam Tip: The size and packing of soil particles (texture) greatly affect how water moves through soil, which is important for understanding drainage and groundwater recharge.

Question 3. (iv) The movement of cooler air from land to sea is called land breeze.
Answer: True: Land breezes happen at night when the land cools down faster than the sea. This causes the air above the land to become cooler and denser, while the air over the warmer sea remains relatively warmer and rises. The cooler, denser air from the land then flows towards the sea to replace the rising warm air.
In simple words: True. A land breeze is cool air that blows from the land towards the sea during the night because the land gets colder than the water.

🎯 Exam Tip: Remember that land and sea breezes are driven by the differential heating and cooling rates of land and water, creating local convection currents near coastlines.

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 receive heat from two main sources for their transformation into water. Firstly, they absorb heat from the surrounding air through convection and conduction. Secondly, they also get heat through conduction from the dish itself, which is in contact with the warmer surroundings. This absorbed heat energy increases the kinetic energy of water molecules, causing them to move more freely and transition from solid ice to liquid water.
In simple words: The ice cubes get heat from the air around them and from the dish they are in. This heat makes the ice melt into water.

🎯 Exam Tip: Melting is an endothermic process, meaning it requires heat energy input. This heat can come from various surrounding objects or the environment.

Question 6. Two test tubes with water are heated by a candle flame as shown in Fig. 7.16. Which thermometers [Fig. 7.16 (a) or Fig. 7.16 (b)] will record a higher temperature? Explain.
Answer: The thermometer in Fig. 7.16 (a) will record a higher temperature. In Fig. (a), the candle flame heats the bottom of the test tube. As the water at the bottom heats up, it becomes less dense and rises due to convection. This warm water moves up and comes into contact with the thermometer, transferring heat to it. In contrast, in Fig. (b), the heat is applied in the middle of the test tube, only heating the specific area directly touched by the flame. Since water is a poor conductor, the heat does not easily spread upwards to the thermometer by conduction. The warm water in Fig. (a) circulates and reaches the thermometer more effectively.
In simple words: The thermometer in Fig. (a) will show a higher temperature. In (a), heating from the bottom makes warm water rise and reach the thermometer. In (b), heating in the middle doesn't let heat travel up to the thermometer easily.

🎯 Exam Tip: This experiment clearly demonstrates convection in liquids. Heating from the bottom allows for the formation of convection currents, efficiently distributing heat throughout the fluid.

Question 7. Why are hollow bricks used to construct the outer walls of houses in hot regions?
Answer: Hollow bricks are used in hot regions because they contain trapped air within them. Air is an excellent insulator of heat, meaning it does not allow heat to pass through easily. The air pockets inside these bricks create a barrier that significantly reduces the transfer of heat from the scorching outside environment into the house. This insulating property helps to keep the interior of the houses much cooler and more comfortable during hot weather.
In simple words: Hollow bricks have air inside them, and air is a good insulator. This trapped air stops outside heat from entering the house, keeping it cool in hot places.

🎯 Exam Tip: Insulation is key to regulating indoor temperatures. Trapped air is a common and effective insulator used in building materials and clothing.

Question 8. Explain how large water bodies prevent extreme temperature in areas around them?
Answer: Large water bodies help prevent extreme temperatures in nearby areas because water heats up and cools down much slower than land. During the day, water absorbs a large amount of solar energy without a significant increase in its own temperature. At night, this absorbed heat is slowly released back into the atmosphere. This slow heating and cooling capacity of water acts as a natural temperature regulator, moderating the air temperature in coastal regions and preventing it from becoming too hot during the day or too cold at night. This stable temperature is vital for local ecosystems.
In simple words: Large water bodies like oceans or big lakes warm up slowly and cool down slowly. They soak up a lot of sun heat during the day and release it slowly at night. This keeps nearby land from getting too hot or too cold.

🎯 Exam Tip: The high specific heat capacity of water is the main reason it acts as a temperature moderator, a key concept in geography and environmental science.

Question. Explain how water seeps through the surface of the Earth and gets stored as groundwater.
Answer: Rainwater, when it falls on the land, begins to seep downwards through tiny holes and spaces in the soil and rocks. This natural process is known as infiltration, and it effectively recharges the surface water. A portion of this rainwater flows into rivers, ponds, and pits, while another part slowly moves downwards through the various layers of soil particles. As it travels deeper, it eventually reaches porous layers of land, where it collects in underground formations called aquifers. This stored water, known as groundwater, can then be drawn up using wells and tubewells, providing a crucial water source for drinking and irrigation, especially during dry seasons. This process is essential for maintaining the underground water table and preventing water scarcity.
In simple words: Rainwater soaks into the ground through tiny gaps in soil and rocks. This process is called infiltration. The water collects deep down in layers called aquifers, becoming groundwater. This stored water is important for drinking and farming.

🎯 Exam Tip: Infiltration and groundwater are vital components of the Earth's water cycle, ensuring a continuous supply of fresh water for ecosystems and human use.

Question 10. The water cycle helps in the redistribution and replenishment of water on the Earth. Justify the statement.
Answer: The water cycle is a continuous process that involves several stages like evaporation, condensation, and precipitation (rain). Through these stages, water moves from the Earth's surface into the atmosphere and then returns to the Earth, ensuring its constant redistribution. Water from rivers, lakes, and oceans evaporates into the air, forms clouds, and then falls back as rain. A part of this rainwater replenishes surface bodies, while another significant portion seeps into the ground, refilling groundwater resources. This constant circulation and renewal of water prevents its permanent loss and ensures that water is always available in different forms and locations across the Earth, supporting life and various ecosystems.
In simple words: The water cycle constantly moves water around the Earth through evaporation, clouds, and rain. It refills rivers, lakes, and underground water. This means water is always spread out and renewed, stopping it from running out completely.

🎯 Exam Tip: Understand that the water cycle is a closed system; water is continuously recycled, making it a fundamental process for sustaining life on Earth.

Heat Transfer in Nature Class 7 Questions and Answers (Intext)

(Page - 90)

Question 1. How does heat get transferred in these materials?
Answer: Heat is transferred in metal utensils primarily through conduction. When one part of the metal is heated, the particles in that area vibrate more vigorously. These vibrating particles then transfer their energy to their neighboring particles, which also start vibrating more. This process continues throughout the metal, effectively moving heat from the hotter end to the cooler end, even though the particles themselves do not change their positions within the material. Metals are very good at this because their particles are closely packed and have free electrons that can quickly carry energy.
In simple words: In metal, heat moves by conduction. Hot particles jiggle and pass their energy to the next particles, slowly moving heat along without the particles themselves moving.

🎯 Exam Tip: Conduction is the main mode of heat transfer in solids. Remember that metals are excellent conductors due to their atomic structure and free electrons.

(Page No. 91)

Question 2. Why we generally use metal utensils for cooking, whereas we prefer clay and porcelain cups for drinking tea
Answer: 
In simple words: 

🎯 Exam Tip: 

(Page No. 92)

Question 3. Why is the smoke going up?
Answer: Smoke goes up because it is a mixture of hot gases and tiny solid particles. The gases in the smoke are heated, causing them to expand and become less dense than the surrounding cooler air. Due to this difference in density, the warmer, lighter smoke rises upwards. This upward movement is a type of convection current, where hot fluid (in this case, smoke) rises, carrying heat and particles with it.
In simple words: Smoke goes up because it is hot. Hot smoke is lighter than the cooler air around it, so it floats upwards.

🎯 Exam Tip: Remember that hot air or gases are less dense and rise, creating convection currents, which explains phenomena like smoke rising or hot air balloons flying.

(Page No. 93)

Question 4. How does heat transfer take place in liquids? Do liquids also rise up when heated like air?
Answer: Heat transfer in liquids primarily occurs through convection. When a liquid is heated, the warmer parts become less dense and rise. Cooler, denser liquid then sinks to take its place, creating a continuous circulation called a convection current. Yes, liquids do rise up when heated, much like air. This happens because heating causes the liquid particles to move faster and spread out, making the heated portion lighter and causing it to float upwards. This is evident when boiling water, where bubbles form and rise to the surface.
In simple words: In liquids, heat moves mostly by convection. Hot liquid gets lighter and rises, while cooler liquid sinks. Yes, hot liquids rise just like hot air does.

🎯 Exam Tip: Convection is crucial for heat transfer in all fluids (liquids and gases). Remember the cycle of less dense hot fluid rising and denser cold fluid sinking.

(Page No. 96)

Question 5. I wonder how heat from the fire reaches us?
Answer: Heat from a fire reaches us mainly through radiation. Radiation is a method of heat transfer that does not require any physical medium (like air or water) between the heat source and the receiver. The fire emits infrared electromagnetic waves, which travel through space and are absorbed by our skin, making us feel warm. This is why you can feel the warmth of a fire even if the air between you and the fire is cold. This is similar to how the sun's heat reaches the Earth through the vast vacuum of space.
In simple words: Heat from a fire reaches us through radiation. Radiation sends out heat waves that travel through the air without needing to touch anything, making us feel warm.

🎯 Exam Tip: Radiation is unique because it can transfer heat even in a vacuum. This is how solar energy reaches Earth and why you feel warmth from a distant fire or radiator.

(Page No. 99)

Question 6. How does water seep through the surface of the Earth?
Answer: Water seeps through the Earth's surface by moving into the many tiny spaces and gaps between the particles of soil, rocks, and other ground materials. These blank places create a network of pores and channels that allow water to slowly filter downwards. The rate at which water seeps depends on the size and interconnectedness of these spaces, as well as the type of soil. For instance, sandy soils with larger gaps allow water to seep faster than clay soils with smaller, more tightly packed particles. This downward movement eventually takes the water deep into the ground, where it replenishes groundwater. This process is essential for providing water for plants and storing water underground.
In simple words: Water seeps into the ground through small gaps between soil particles. It slowly moves down through these spaces, going deeper into the Earth.

🎯 Exam Tip: The porosity and permeability of the ground are key factors determining how quickly and deeply water can infiltrate the Earth's surface to become groundwater.