7 Grade Science Unit 8 Transmission of Heat

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Ans: We use cooking pots made of metals because they are good conductors of heat.

2. What is convection current?

Ans: The upward movement of warm water and downward monument of colder water is called a convection current.

3. Which surface does absorb maximum heat?

Ans: The black surface absorbs maximum heat.

4. Why do we use woolen clothes during winter days?

Ans: we use woolen clothes and blankets on winter days because they slow down the transfer of heat.

5. What is the advantage of the gliding flight for a bird?

Ans: The advantage of the gliding flight for a bird is that during a gliding flight a bird does not move its wings but glides on wind currents and saves a lot of energy.

6. What is convection? How does it occur?

Ans: The transfer of heat in which molecules of a medium move to the source of heat energy to absorb heat and then move away from it is called convection.

7. Define thermal energy?

Ans: The energy of the motion of particles matter is called thermal energy.

8. What is the meaning of thermal?

Ans: The meaning of thermal is heat.

9. How does heat flow?

Ans: Heat flows from an object of higher temperature to an object of lower temperature.

10. Explain the transmission of heat?

Ans: The transfer of heat from one object to the other is called the transmission of heat.

11. In which medium heat transfer?

Ans; Solids, liquids, and gases.

12. How particles are held in solids?

Ans: In solids, particles are held very close to each other.

13. Explain good conductor?

Ans: Materials that allow heat to flow through them easily are called good conductors of heat.

14. Give examples of good conductors?

Ans: Solids such as metals are good conductors of heat.

15. Define bad conductors?

Ans: Materials that do not allow heat to flow through them easily are called bad conductors.

16. Examples of bad conductors?

Ans: Solids like wood, glass, and plastics are bad conductors of heat.

16. Which liquid is a good conductor of heat?

Ans: Mercury is a good conductor of heat.

17. Which insulating material is used in the walls of the refrigerators?

Ans: Styrofoam is used between the double walls of the refrigerators.

18. Examples of the effect of convection.

Ans: Winds and ocean currents are examples of the effects of convection.

19. Define radiations?

Ans: The transfer of heat from a hot body to a cold body directly without heating the space in between the two bodies is called radiation.

20. Which medium is required for the heat from the sun or heater to us by radiation?

Ans: No medium is required.

21. Do good absorbers of heat also good radiators of heat?

Ans: Yes, a good absorber of heat is also a good radiator of heat.

22. Which surface is a good absorber and a good radiator of heat, black or shiny?

Ans: The black surface is a good absorber and radiator.

23. Why fins at the back of refrigerators are painted black?

 Ans: Fins at the back of the refrigerators are painted black to emit heat.

24. How vacuum is created in a vacuum flask?

Ans: Vacuum flask is two-walled. The air between the two walls is removed to create a vacuum.

25. How does a vacuum flask reduce the transfer of the heart?

Ans: Vacuum reduces the transfer of heat by conduction, convection, and radiation.

26. Define convection.

Ans: The transfer of heat in which molecules of a medium actually move to the source of heat energy to absorb heat and then move away from it is called, convection.