Chapter 4- Heat-Class 7 Question and Answer (Long)

Chapter 4 – Heat – Long Questions and Answers(Solved Worksheet)

Question- Explain why our sense of touch is not always reliable in determining the temperature of objects.

Answer- Our sense of touch is not always reliable in determining the temperature of objects because it depends on individual sensitivity and can be misleading in extreme cases. For example, in the case of very hot or very cold objects, our sense of touch might not give an accurate assessment of the object’s temperature. Furthermore, our sense of touch doesn’t provide precise temperature measurements, which could lead to inaccurate conclusions about an object’s actual temperature.

Question- How does a clinical thermometer work?

Answer- A clinical thermometer works by using mercury inside a bulb, which expands and contracts with temperature changes. When the thermometer is placed in a warm environment, the mercury inside the bulb expands, causing the mercury column to rise. Conversely, in a cooler environment, the mercury contracts, causing the mercury column to fall. The scale on the thermometer, marked in degrees Celsius, helps in measuring the temperature accurately.

Question- Explain the step-by-step process of reading body temperature using a thermometer.

Answer- Begin by understanding the scale on the thermometer and noting the bigger marks and divisions. Ensure the thermometer is clean, preferably washed with an antiseptic solution. Tap the thermometer gently to position the mercury or indicator at a lower point on the scale. For body temperature measurement, place the bulb of the thermometer under the tongue for approximately one minute, ensuring accurate measurement. Finally, take out the thermometer and carefully observe and note the temperature reading, including the unit (°C).

Question- Discuss the concerns associated with the use of mercury in thermometers and mention the alternative available.

Answer- Mercury in thermometers raises concerns due to its toxic nature, posing health risks if released from a broken thermometer. Its disposal is also challenging and potentially harmful to the environment and people. An alternative to mercury thermometers is digital thermometers, which are safer, easier to read, more durable, and environmentally friendly.

Question- What are the precautions that need to be taken while using a clinical thermometer?

Answer- Several precautions need to be taken while using a clinical thermometer. Firstly, ensure that it’s clean, preferably using an antiseptic solution. Before using, check that the mercury level is below 35°C. When reading the thermometer, the mercury level should be along your line of sight, and avoid holding the thermometer by the bulb to prevent heat transfer from the hand. Additionally, handle the thermometer with care as it is delicate and can break easily.

Question- Explain the key precautions to take when using a laboratory thermometer to ensure accurate temperature readings.

Answer- While using a laboratory thermometer, ensure it is kept upright and not tilted, as tilting can affect accuracy. The bulb of the thermometer should be entirely surrounded by the substance whose temperature is being measured, and it should not touch the container’s surface. This approach helps in getting an accurate measurement of the substance’s temperature and not the container’s temperature.

Question- Can you explain the experiment involving a metal rod or flat strip attached to small wax pieces for understanding heat transfer?

Answer- In the experiment, a metal rod or flat strip is attached with small wax pieces at equal distances and clamped to a stand. One end of the rod is heated, and observations are made on the melting of the wax pieces. Heat travels from the hotter end of the rod to the colder end, causing the wax pieces to melt, demonstrating the process of conduction in solids.

Question- How do different materials affect the conduction of heat, and how is this principle applied practically?

Answer– Different materials have varying heat conductivity. Metals are good conductors of heat, while materials like plastic and wood are poor conductors. This principle is practically applied, for instance, in the handles of cooking pans. Since metal handles would get very hot and could cause burns, plastic or wooden handles are used because they stay cooler, being poor conductors of heat.

Question- Can you explain the process and rationale behind using various materials and hot water in the experiment to determine their conductivity?

Answer- Different materials are dipped into hot water, and the non-dipped ends are touched to feel the temperature. Materials that feel hot are classified as conductors because they allow heat to pass through, and those that remain cool are classified as insulators.

Question- How does the ability or inability of materials to conduct heat influence their practical applications in real life?

Answer- Good conductors are used in scenarios where heat transfer is necessary, like in cooking utensils, while insulators are used where prevention of heat transfer is needed, such as in the handles of cooking utensils.

Question- Can you explain the process of convection as observed in the heating of water during the experiment?

Answer- Convection in water occurs when the water near the heat source gets hot and rises, making room for the cooler water to move down towards the heat source, get heated, and rise again, creating a continuous circulation of water and heat.

Question- How does the concept of convection explain the natural phenomenon of sea breeze and land breeze in coastal areas?

Answer- In coastal areas, due to the differential heating and cooling rates of land and sea, air moves from the cooler region to the hotter region, causing sea breezes during the day and land breezes during the night due to the convection currents.

Question- Describe the process of convection as it occurs in water, as observed in the experiment.

Answer- In the experiment, as the water is heated, the part near the flame becomes hot and rises due to decreased density. Colder water then moves down to replace the risen hot water, getting heated in turn. This continuous cycle of rising hot water and descending cold water heats the entire volume of water, demonstrating the process of convection.

Question- How does convection contribute to the sea breeze and land breeze phenomenon observed in coastal areas?

Answer- Convection contributes to this phenomenon due to the varying heating and cooling rates of land and sea. During the day, land heats up faster, causing the air above to become hot and rise, and the cooler sea air replaces it, resulting in a sea breeze. At night, the process reverses, with the cooler land air moving towards the sea, causing a land breeze.

Question- Can you explain how the sea breeze phenomenon occurs and how it affects the coastal areas during the day?

Answer- The sea breeze phenomenon occurs when the sun heats the Earth’s surface, causing the land to heat up faster than the sea. The warmer air over the land rises, creating a low-pressure area, and cooler air from the sea rushes in to replace it, resulting in a sea breeze. This breeze brings cooler air from the sea onto the land, providing relief from heat in coastal areas during the day.

Question- How does the land breeze differ from the sea breeze, and what effects does it have?

Answer- The land breeze occurs at night when the land cools down faster than the sea. Cooler air from the land moves towards the warmer sea, creating a breeze known as the land breeze. This breeze can lead to cooler nighttime temperatures and can affect local weather patterns, often being felt as a gentle wind blowing from the land towards the sea.

Question- Can you explain how radiation differs from conduction and convection in terms of heat transfer?

Answer- Radiation differs from conduction and convection as it doesn’t require a medium like air or water to transfer heat. Radiation allows heat to move through space, even in the absence of any material substance, enabling the transfer of heat energy from hot bodies or objects to other objects through emitted radiation.

Question- How does radiation play a role in our daily life, and how do our bodies interact with radiative heat?

Answer- In our daily life, our bodies continuously give off heat to the surroundings and receive heat from the environment through radiation. For instance, we feel warmth through radiation when sitting in front of a room heater or when exposed to the sun. Objects like umbrellas can be used to shield our bodies from direct heat radiation from the sun, helping to keep us cooler.

Question- Can you explain how trapped layers of air in hollow bricks contribute to energy efficiency in buildings?

Answer- Trapped layers of air in hollow bricks act as insulators against external heat and cold. In hot weather, they resist the entry of heat, and in cold weather, they prevent the escape of internal warmth, reducing the dependency on artificial heating and cooling systems, thus contributing to energy efficiency.

Question- How does the use of hollow bricks with trapped air layers impact the environment and the cost-effectiveness of a building?

Answer- The use of hollow bricks minimises the need for artificial heating and cooling, reducing energy consumption and its environmental impact. While the initial cost might be higher, the long-term benefits, such as reduced utility bills due to energy savings, make it a cost-effective choice.

Question- Can you explain the experimental observation made with two tin cans, one painted black and the other white, when filled with equal amounts of water and placed in the sun?

Answer- In the experiment, the black-painted can absorbs more sunlight, converting it into heat, making the water warmer compared to the white-painted can, which reflects most of the sunlight and remains cooler due to less heat absorption.

Question- How does the choice of clothing colours based on their heat-absorbing properties impact our comfort in different seasons?

Answer- Choosing light-coloured clothes in summer reflects more sunlight, keeping us cooler, while dark-coloured clothes in winter absorb and retain more heat, helping to stay warm. This alignment with the heat-absorbing properties of colours enhances comfort in varying seasonal temperatures.

Question- Can you elaborate on the role of trapped air in woollen clothes and blankets in terms of insulation?

Answer- Trapped air within woollen fibres or between blankets acts as a barrier against the cold. Being a poor conductor of heat, this air prevents the body’s heat from escaping, keeping individuals warm in cold conditions.

Question- How does the choice between one thick blanket and two thin blankets impact insulation and warmth?

Answer- Choosing two thin blankets results in a layer of trapped air between them, providing better insulation by preventing the escape of body heat and the intrusion of external cold, ensuring a warmer feeling compared to a single thick blanket.

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