Extra Questions for Chapter 7 Heat Transfer in Nature Class 7 Science Curiosity
Class 7 Science Heat Transfer in Nature Extra Questions
Very Short Answer Questions
Question 1. How does heat flow from one object to another?
Answer
Heat flows from a hotter object to a colder object.
Question 2. Does the transfer of heat by radiation require any medium?
Answer
The transfer of heat by radiation does not require any medium.
Question 3. Do all hot bodies radiate heat?
Answer
Yes, all hot bodies radiate heat.
Question 4.What are woollen clothes made from?
Answer
Woollen clothes are made from the wool obtained from animals like sheep, goats, and yaks.
Question 5. Explain land breeze.
Answer
The water cools down more slowly at night than the land. So, the cool air from the land moves towards the sea. This is called the land breeze.
Question 6. Why are light-coloured clothes preferred during summer?
Answer
Light-coloured clothes are preferred during summer because they reflect heat and help keep the body cool.
Question 7. What are conductors and insulators of heat?
Answer
Conductors allow the flow of heat, while insulators do not. Examples of conductors include copper and iron, while wood and rubber are insulators.
Question 8. What is the temperature range for a healthy person's body temperature in Fahrenheit?
Answer
A healthy person's average body temperature ranges from 98.6°F to 98.8°F.
Question 9. Who devised the Celsius scale for measuring temperature?
Answer
Swedish astronomer Anders Celsius devised the Celsius scale in 1742.
Question 10. What is the freezing point and boiling point of water in Celsius and Fahrenheit scales?
Answer
In Celsius, water freezes at 0°C and boils at 100°C. In Fahrenheit, water freezes at 32°F and boils at 212°F.
Question 11. What is the purpose of a thermometer?
Answer
A thermometer is used to measure the temperature of an object, indicating how cold or hot it is.
Question 12. What precautions should be taken when using a clinical thermometer?
Answer
Precautions include washing the thermometer before and after use, not holding it near the bulb, and placing the mercury level along the eyesight.
Question 13. Why are woollen clothes effective in keeping us warm?
Answer
Woollen clothes trap air in their pores, and air is a poor conductor of heat, reducing heat loss from the body to the surroundings, keeping us warm.
Question 14. What is an ice stupa, and what is its purpose?
Answer
An ice stupa is a cone-shaped ice structure in Ladakh, formed by freezing water in winter. It melts slowly in spring to provide water for farming and daily use.
Question 15. What is groundwater, and how is it accessed?
Answer
Groundwater is water stored in pores of sediments or cracks in rocks below the Earth’s surface, called aquifers. It can be used by digging wells or drilling bore wells
Question 16. How does heat transfer occur in convection?
Answer
Heat transfer in convection occurs through the movement of particles in a medium, such as liquids or gases.
Question 17. Define heat.
Answer
Heat is a form of energy which produces a sensation of warmth and flows when there is a temperature difference between two bodies. It is measured in joules or calories.
Question 18. Which device is used to measure temperature?
Answer
Thermometer is used to measure temperature.
Question 19. What is the significance of the kink in a clinical thermometer?
Answer
The kink in a clinical thermometer prevents the mercury from falling down rapidly after use, allowing the temperature to be noted conveniently and accurately.
Question 20. What is Conduction?
Answer
The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.
Question 21. What is the concern associated with the use of mercury thermometers?
Answer
There is a lot of concern over the use of mercury in thermometers. Mercury is a toxic substance and is very difficult to dispose of if a thermometer breaks.
Question 22. How does heat transfer in solids?
Answer
In solids, generally, the heat is transferred by the process of conduction.
Question 23. Why does the level of mercury rise when its bulb comes in contact with a hot object?
Answer
Mercury expands when heated, causing its level to rise in the capillary tube of the thermometer.
Question 24. What are conductors and insulators of heat? Provide examples of each.
Answer
Conductors are materials that allow the flow of heat, such as copper and iron. Insulators are materials that do not allow the flow of heat, such as wood, rubber, and glass.
Short Answer Questions
Question 1. How water get heated when kept on flame?
Answer
When water is heated, the water near the flame gets hot. Hot water rises up. The cold water from the sides moves down towards the source of heat. This water also gets hot and rises and water from the sides moves down. This process continues till the whole water gets heated. This mode of heat transfer is known as convection.
Question 2. To keep her soup warm, Paheli wrapped the container in which it was kept with woollen clothes. Can she apply the same method to keep a glass of cold drink cool? Give a reason for your Answer.
Answer
Yes, she can use the same method to keep a glass of cold drink cool because:
- Wool is a thermal insulator.
- It prevents heat from passing through.
- This helps maintain the cold temperature of the drink.
Question 3. A laboratory thermometer A is kept 7 cm away on the side of the flame while a similar thermometer B is kept 7 cm above the flame of a candle as shown in the figure. Which of the thermometers A or B will show a greater rise in temperature? Give a reason for your answer.
Answer
Thermometer B will show a greater rise in temperature because:
- The heated air above the candle rises quickly.
- This increases the temperature of the bulb of thermometer B more than that of thermometer A.
Question 4. A circular metal loop is heated at point O as shown in the figure.
(a) In which direction, would heat flow in the loop?
(b) In which order, are the pins at points P, Q and R fixed with the help of wax fall if points O, P, Q and R are equidistant from each other?
Answer
(a) Heat will flow in both directions from O to P and from O to R.
(b) First of all, the pin at P and R will fall simultaneously. After that, the pin at Q will fall.
Question 5. For setting curd, a small amount of curd is added to warm milk. The microbes present in the curd help in setting if the temperature of the mixture remains approximately between 35°C to 40°C. At places where room temperature remains much below the range, setting of curd becomes difficult. Suggest a way to set curd in such a situation.
Answer
To set curd in cooler conditions, follow these steps:
- Use a thermally insulated cover for the container.
- Wrap the container with wool or jute sacks to maintain warmth.
- Ensure the mixture stays at a temperature between 35°C and 40°C.
This helps create a suitable environment for the curd to set properly.
Question 6. Shopkeepers selling ice blocks usually cover them with jute sacks or sawdust. Explain why.
Answer
Jute sacks or sawdust are commonly used to cover ice blocks for the following reasons:
- They act as insulating materials, helping to maintain the temperature of the ice.
- This insulation reduces the rate at which the ice melts.
- By covering ice blocks, shopkeepers can ensure that the ice lasts longer for customers.
Question 7. While constructing a house in coastal area, in which direction should the windows preferably face and why?
Answer
The windows should ideally face towards the sea for the following reasons:
- The sea breeze helps to keep the house cool during the day.
- This positioning allows for better ventilation and comfort.
At night, the situation reverses, as the land cools faster than the sea, leading to a land breeze that can also be beneficial.
Question 8. Explain the process of conduction with an example.
Answer
Conduction is the transfer of heat in solids through direct contact. In this process, heated particles vibrate and pass energy to nearby particles.
For example, when a metal pan is placed on a flame, heat travels from the bottom to the entire surface, making the pan hot. Metals are used for cooking because they are good conductors of heat.
Question 9. What is convection and how does it affect coastal areas?
Answer
Convection is heat transfer in liquids and gases where warm particles rise and cool ones sink. In coastal areas, during the day, land heats up faster than sea, causing a sea breeze. At night, land cools faster, creating a land breeze. These breezes are examples of convection currents and provide comfort in coastal climates.
Question 10. Describe radiation and give two real-life applications.
Answer
Radiation is the transfer of heat through invisible waves, without needing a medium. For example, the Sun heats the Earth through radiation. Another example is the warmth felt near a fire. Light-coloured clothes reflect radiation, keeping us cool, while dark-coloured clothes absorb heat, keeping us warm in winter.
Question 11. How does the water cycle help in redistributing water on Earth?
Answer
The Sun's heat drives the water cycle through evaporation, condensation, precipitation, and seepage. Water evaporates from oceans and lakes, forms clouds, and falls back as rain or snow. Some of this water seeps underground to become groundwater. This cycle keeps water circulating and available across regions.
Question 12. What are ice stupas and how do they help conserve water in Ladakh?
Answer
Ice stupas are cone-shaped ice structures built in Ladakh to store water in winter. Stream water is frozen in these shapes and melts slowly in spring, providing water for farming. They help solve water scarcity in dry, mountainous areas and are an example of traditional knowledge used for modern conservation.
Question 13. Define temperature. What is its unit?
Answer
A reliable measure of the hotness of an object is its temperature. Temperature is measured by a device called a thermometer. The unit of temperature is degree Celsius (°C), Fahrenheit, and Kelvin (SI unit).
Question 14. What is the use of the maximum-minimum thermometer?
Answer
The maximum-minimum thermometer is used to measure the highest and lowest temperatures of a place in a day. It is commonly used in weather stations to track daily temperature variations. This thermometer helps in understanding temperature fluctuations, which is essential for weather forecasting and analysis.
Question 15. Why conduction is only possible in solids?
Answer
In solids, generally, the heat is transferred by the process of conduction because particles of solids are closely packed, and heat is transferred from the hotter end to the colder end of an object.
Question 16. How does the heat from the sun reach us?
Answer
Heat from the sun reaches us by radiation, which does not require a medium to transfer heat. Unlike conduction (which occurs in solids) and convection (which occurs in liquids and gases), radiation can transfer heat even through the vacuum of space.
Question 17. Explain how water is heated by convection.
Answer
The water is a poor conductor of heat, so do not heat it by conduction. When water is heated, the water becomes lighter. Hot water rises up. The cold water from the sides moves down towards the source of heat. This water also gets hot and rises upward, and water from the sides moves down. This process continues till the whole water gets heated. This mode of heat transfer is known as convection.
Question 18. Differentiate between conductor and insulators?
Answer
The materials which allow heat to pass through them easily are conductors of heat. For example, aluminium, iron, and copper. The materials that do not allow heat to pass through them easily are poor conductors of heat, known as insulators, such as plastic and wood.
Question 19. In a mercury thermometer, the level of mercury rises when its bulb comes in contact with a hot object. What is the reason for this rise in the level of mercury?
Answer
When the bulb of a mercury thermometer touches a hot object, heat transfers from the object to the mercury. This causes the mercury to:
- Expand due to the increase in temperature.
- Rise in the capillary tube, indicating a higher temperature.
Question 20. Explain sea breeze.
Answer
During the day, the land gets heated faster than the water. The air over the land becomes hotter and rises up. The sea's cooler air rushes towards the land to take its place. The warm air from the land moves towards the sea to complete the cycle. The air from the sea is called the sea breeze.
Question 21. Describe the Celsius and Fahrenheit temperature scales and their freezing and boiling points for water.
Answer
The Celsius scale was devised by Anders Celsius, with 0°C as the freezing point of water and 100°C as the boiling point. In the Fahrenheit scale, water freezes at 32°F and boils at 212°F.
Question 22. How do laboratory thermometers differ from clinical thermometers?
Answer
Laboratory thermometers have a longer stem and bulb compared to clinical thermometers. They also typically have only the Celsius scale, and they are used for measuring higher temperatures.
Question 23. Explain the three modes of heat exchange: conduction, convection, and radiation.
Answer
Conduction is the transfer of heat within an object without the movement of particles. Convection is the transfer of heat through the movement of particles in a medium like liquids and gases. Radiation is the transfer of heat through electromagnetic waves, such as from the sun to the Earth.
Question 24. Why is wool considered a good choice for winter clothing?
Answer
Wool is a good choice for winter clothing because it is an excellent insulator and a poor conductor of heat. It traps air between its fibres, creating an insulating barrier that prevents the flow of heat from the body to the cold surroundings, thus keeping the body warm.
Question 25. Why is it important to use digital thermometers instead of mercury thermometers?
Answer
It is important to use digital thermometers because mercury is toxic, and it can be hazardous if a mercury thermometer breaks. Digital thermometers do not contain mercury and are safer to use.
Question 26. How does heat transfer occur in conduction, and give an example?
Answer
Heat transfer in conduction occurs when heat is transferred from a hotter part of an object to a colder part through direct contact. An example is when popcorn is popped in a cooker on a flame, and heat is transferred from the flame to the corn kernels.
Question 27. Why are the pipes of the solar heater and the containers of the solar cooker painted black?
Answer
The pipes of the solar heater and the containers of the solar cooker are painted black because:
- Black colour absorbs more heat than other colours.
- This helps to keep the pipes and containers warm.
Long Questions and Answers
Question 1. Why do coastal areas experience land breeze and sea breeze?
Answer
In coastal areas, the movement of air between land and sea causes land breeze and sea breeze.
Sea Breeze (Daytime):
 |
| Sea Breeze |
- During the day, the land heats up faster than the sea.
- The air above the land becomes hot and rises, while cooler air from the sea moves in to take its place.
- This movement of air from the sea to the land is called sea breeze.
 |
| Land Breeze |
- At night, the land cools down faster than the sea.
- The air above the sea remains warmer and rises, and the cooler air from the land moves towards the sea.
- This movement of air from the land to the sea is called land breeze.
These breezes help moderate temperatures in coastal areas, making them more comfortable.
Question 2. How does heat transfer take place in solids, liquids, and gases?
Answer
Heat can be transferred in three different ways depending on the medium:
Conduction (Solids)
- In solids, heat travels from one particle to another without movement of the particles.
- Example: A metal spoon gets hot when placed in a cup of tea.
Convection (Liquids & Gases)
- In liquids and gases, heat moves through rising hot particles and falling cold particles.
- Example: Boiling water in a pan shows upward movement of hot water and downward movement of cold water.
Radiation (without Medium)
- Heat can also be transferred without any medium in the form of rays.
- Example: Heat from the Sun reaches Earth through space by radiation.
Thus, different materials transfer heat in different ways, and understanding these helps in designing better insulators and conductors.
Question 3. Two objects at the same temperature, one smaller than the other, are placed together. In which direction will the heat be transferred? Give reason.
Answer
There will be no heat transfer between the two objects because:
- Heat flows only from a higher-temperature object to a lower-temperature object.
- Since both objects are at the same temperature, there is no temperature difference.
- As a result, no heat flow occurs, regardless of their size.
Question 4. Why do hollow bricks help maintain comfortable indoor temperatures in houses?
Answer
- Hollow bricks contain air trapped in their hollow parts, which acts as a poor conductor of heat.
- In winter, this trapped air reduces heat loss from the house to the cold outside, keeping it warm.
- In summer, it slows heat gain from the hot outside, keeping the house cool.
This insulation property helps maintain a comfortable indoor temperature year-round.
Question 5. What is seepage, and how does it depend on the type of soil?
Answer
Seepage is when water soaks into the ground through soil or rocks, becoming groundwater. The speed of seepage depends on soil type.
- Gravel has big spaces between particles, so water flows fast.
- Sand has smaller spaces, so water moves slower.
- Clay has tiny spaces, so water seeps very slowly.
For example, in the activity with bottles, water flows fastest through gravel, slower through sand, and slowest through clay (as shown below).
Question 6. How does the Sun’s heat cause precipitation in the water cycle? Give an example.
Answer
The Sun’s heat cause precipitation in the water cycle as
- The Sun’s heat evaporates water from oceans and rivers into vapour, which rises into the sky.
- The vapour cools and condenses into clouds made of tiny water droplets.
- When clouds get heavy, they release water as precipitation, like rain or snow.
For example, after a sunny day, you might see rain because the Sun’s heat made water vapour form clouds that then rained.
Question 7. State similarities between the laboratory thermometer and the clinical thermometer.
Answer
Similarities between laboratory thermometer and clinical thermometer are:
- Both are used to measure temperature.
- Both typically use mercury or digital technology to display readings.
- Both require careful handling to ensure accurate readings.
- Both thermometers have a scale marked in degrees Celsius.
Question 8. Describe how convection creates land and sea breezes. Suggest one way people in coastal areas can use this knowledge.
Answer
Land and Sea Breezes:
- During the day, the land near the beach heats up faster than the water in the sea. This is because different materials absorb heat at different rates.
- However, at night, the situation changes: the land cools down faster than the water.
- This difference in how quickly land and water heat up and cool down is what causes the land and sea breeze.
People in coastal areas can plan outdoor activities, like picnics, in the afternoon when the sea breeze makes it cooler and more comfortable, instead of the hot morning when the land is warmest.
Question 9. Explain the water cycle’s role in providing fresh water, including all main processes. Describe how ice stupas in Ladakh help with water scarcity.
Answer
The water cycle is the continuous movement of water on, above and below the surface of the Earth.
 |
| Water cycle |
It has the following main four processes:
- Evaporation: The Sun’s heat turns water from oceans, rivers, and lakes into vapour. Plants add vapour through transpiration.
- Condensation: Vapour rises, cools, and forms clouds of tiny water droplets.
- Precipitation: Clouds release water as rain, snow, or hail, which fills rivers, lakes, and groundwater.
- Seepage and Runoff: Some water soaks into the ground as groundwater, and some flows into rivers and oceans. This cycle brings fresh water to places where people and plants need it, like rivers for drinking or rain for crops.
In Ladakh, they make ice stupas, an artificial ice cones built in winter. These ice stupas melt slowly in warmer months, providing water for farming and daily use.
Question 10. Explain the reason for the following statement, “When heat is applied at the bottom of the water vessel, then it gets heated more quickly than when it is heated at the top.”
Answer
The reason for the statement is related to the movement of water particles when heated:
- When heat is applied at the bottom of the vessel, the water particles near the heat source become lighter and rise.
- As the hot water rises, the colder and heavier water from the sides moves down to replace it.
- This creates convection currents, allowing the water to heat up more efficiently.
- Conversely, when heat is applied at the top, only the upper layer of water heats up, while the hot water remains at the surface.
Question 11. Ventilators are situated close to the ceilings and not near the floor. Why?
Answer
Ventilators are placed near the ceilings rather than the floor for several reasons:
- Warm air is lighter than cool air, causing it to rise.
- As warm air rises, it creates a vacuum that pulls in cooler air from below.
- Ventilators at the top help to circulate fresh air effectively.
This design enhances overall air quality in the room.