All questions of Heat for Class 7 Exam

• ​Desert biomes 
  • Sand absorbs as well as radiates heat more quickly than the earth.
  • Thus at night, the temperature of sand decreases at a much faster rate making the surroundings cooler in deserts.
  • Nights are cooler in the deserts than in the plains because Sand radiates heat more quickly than the earth.  Hence, Option 1 is correct.
  • Because deserts have such little water vapor in the air, it makes it harder to trap heat or cold in a desert. 
  • At night, the sun no longer heats the desert and the heat from the day doesn't stay trapped. 
  • Because of this, some deserts can get cold at night, dropping to below 40F, which is coat weather.

Both clinical and laboratory thermometers are made of glass and filled with mercury, which expands and contracts uniformly with temperature changes, allowing accurate readings.

Explanation:

Wooden Spoon
When a wooden spoon is dipped in a cup of ice cream, the wooden material of the spoon does not conduct heat as efficiently as metal.

Insulating Properties
Wood is a poor conductor of heat compared to metal. This means that the heat from the ice cream does not transfer as easily through the wooden spoon to the other end. As a result, the other end of the spoon does not become cold when dipped in the ice cream.

Conduction, Convection, Radiation
Conduction is the transfer of heat through direct contact, but in this case, the wooden spoon does not conduct heat well. Convection is the transfer of heat through a fluid or gas, which is not applicable here. Radiation is the transfer of heat through electromagnetic waves, but the scenario described does not involve significant radiation.

Conclusion
In conclusion, when a wooden spoon is dipped in a cup of ice cream, the other end of the spoon does not become cold because wood is a poor conductor of heat. Therefore, the ice cream does not significantly affect the temperature of the entire spoon.

Conductor of Heat
Wood, plastic, iron, and rubber are all materials with different properties when it comes to conducting heat. Among these options, iron is the best conductor of heat. Here's why:

Conduction of Heat
- Heat conduction is the process where heat energy is transferred from one substance to another through direct contact.
- Materials that are good conductors of heat allow heat to pass through them easily.

Iron as a Conductor of Heat
- Iron is a metal that has a high thermal conductivity, meaning it can transfer heat efficiently.
- When heat is applied to iron, its particles vibrate and transfer the heat energy to neighboring particles quickly.
- This property is why iron is commonly used in cooking utensils, radiators, and other applications where heat transfer is necessary.

Comparison with Other Materials
- Wood and plastic are poor conductors of heat, which is why they are often used as insulating materials to prevent heat transfer.
- Rubber is also a poor conductor of heat, making it suitable for applications where heat insulation is required.

Conclusion
In conclusion, iron is the best conductor of heat among the given options. Its high thermal conductivity allows for efficient heat transfer, making it a common choice for various applications where heat conduction is essential.

Why Plastic is the Ideal Material for a Saucepan Handle
Plastic is the most suitable material for the handle of a saucepan for several reasons.

Does not Conduct Heat
One of the main reasons why plastic is preferred for saucepan handles is that it does not conduct heat. When cooking, the handle of a saucepan can get very hot, making it difficult to hold without the risk of burning yourself. Plastic handles remain cool to the touch, providing a comfortable and safe grip while cooking.

Comfort and Safety
Plastic handles are generally more comfortable to hold compared to metal or other materials. They are lightweight and do not transfer heat, making them easier to grip for longer periods without discomfort. This is especially important when dealing with hot liquids or heavy pots.

Durability and Longevity
Plastic handles are often more durable and long-lasting than other materials like metal or wood. They are resistant to rust, corrosion, and wear, making them a practical choice for a saucepan handle that will be used frequently.

Easy to Clean
Plastic handles are easy to clean and maintain. They can be washed with soap and water without the risk of damage or deterioration. This makes them a hygienic choice for kitchen utensils that come in contact with food.

Conclusion
In conclusion, plastic is the ideal material for a saucepan handle due to its non-conductive properties, comfort, durability, and ease of maintenance. When choosing a saucepan, opt for one with a plastic handle for a safe and enjoyable cooking experience.

Understanding Heat Transfer Processes
Heat can be transferred through three main processes: conduction, convection, and radiation. Each of these processes has unique characteristics regarding the medium required for heat transfer.
Conduction
- In conduction, heat is transferred through direct contact between molecules.
- This process requires a solid medium (e.g., metal) as the heat is passed from one molecule to another.
Convection
- Convection involves the transfer of heat through fluids (liquids or gases).
- It occurs when warmer areas of a fluid rise and cooler areas sink, creating a circulation pattern.
- This process also requires a medium, specifically a fluid.
Radiation
- Radiation is the only heat transfer process that does not require a medium.
- It involves the transfer of energy through electromagnetic waves, such as infrared radiation.
- Heat from the sun reaches the Earth through the vacuum of space, demonstrating that radiation can occur without any material medium.
Conclusion
- The correct answer to the question is option 'C' (Radiation) because it uniquely allows for heat transfer across empty space.
- Understanding these processes is essential in various scientific and practical applications, from cooking to climate science.

Multiple layers of clothing trap air between them, and since air is a poor conductor of heat, it acts as an insulator, keeping the body warmer.

White paint reflects most of the heat in hot climates, making it the ideal choice for the outer walls of houses. Here's why:
White color reflects heat
- White surfaces reflect most of the sunlight that hits them, which helps to keep the house cooler.
- This is because white color does not absorb as much heat as darker colors, preventing the walls from becoming too hot.
Benefits of using white paint in hot climates
- By reflecting heat, white paint helps to maintain a comfortable temperature inside the house, reducing the need for excessive air conditioning.
- This can lead to lower energy bills and a more sustainable living environment.
- Additionally, white paint can help to prolong the lifespan of the walls by reducing heat-related damage and deterioration.
Conclusion
In conclusion, painting the outer walls of houses in hot climates white is a practical and cost-effective solution to combat the heat. By reflecting most of the heat and sunlight, white paint can help to create a more comfortable living space while also saving on energy costs in the long run.

Copper is a better conductor of heat than stainless steel, which allows for more even heating and better cooking efficiency.