Imp Questions For All Chapters – General Science Class 7
Heat
Short Questions
1. What is heat?
→ Heat is a form of energy that causes a rise in temperature or a change in state.
2. In which direction does heat flow?
→ Heat always flows from a hot object to a cold object.
3. How is heat transferred?
→ Heat is transferred by conduction, convection, and radiation.
4. What is conduction?
→ Conduction is the transfer of heat through a solid material without movement of the substance.
5. Which materials are good conductors of heat?
→ Metals like copper, iron, and aluminum.
6. Which materials are bad conductors (insulators) of heat?
→ Wood, plastic, rubber, and glass.
7. What is convection?
→ Convection is the transfer of heat in liquids and gases through the movement of particles.
8. Give an example of convection.
→ Boiling water: Hot water rises, and cold water moves down, creating a cycle.
9. What is radiation?
→ Radiation is the transfer of heat without a medium, in the form of heat waves.
10. Give an example of radiation.
→ The Sun’s heat reaches Earth through radiation.
11. Why do we wear woolen clothes in winter?
→ Wool traps air, which acts as an insulator, keeping us warm.
12. Why are houses in hot regions painted white?
→ White reflects most of the heat, keeping the house cool.
13. Why does metal feel colder than wood in winter?
→ Metal is a good conductor, so it quickly transfers heat away from our hands.
14. What is expansion of substances due to heat?
→ When heated, solids, liquids, and gases expand (increase in size).
15. Why do telephone wires sag in summer and become tight in winter?
→ Heat causes expansion in summer and contraction in winter.
Long Questions
1. Why does a halwai wrap a cloth around the handle of his spoon while stirring hot milk?
→ Metal is a good conductor of heat, so it becomes very hot. Wrapping a cloth prevents heat transfer, making it safe to hold.
2. Why do we wear woolen clothes in winter?
→ Wool traps air, which is a bad conductor of heat, keeping our body warm by preventing heat loss.
3. How does heat transfer through conduction?
→ In conduction, heat moves from the hot part to the cold part of a solid object, like a metal rod heated at one end.
4. How does heat transfer through convection?
→ In convection, hot fluids (liquids or gases) rise, and cold fluids sink, forming a cycle that distributes heat evenly.
5. Why are houses in Rajasthan painted white?
→ White color reflects most of the sun’s heat, keeping the house cool during hot summers.
6. Why are heaters placed near the floor and ACs near the ceiling?
→ Hot air rises and cold air sinks, so heaters warm the room from below, while ACs cool from above using convection.
7. How does a thermos flask keep liquids hot or cold?
→ A thermos flask has vacuum walls that prevent conduction and convection, and a silver lining that reflects heat to reduce radiation.
8. Why does an iron pillar feel colder than a wooden pole in winter?
→ Iron is a good conductor of heat, so it quickly absorbs heat from our hand, making it feel cold, while wood is a bad conductor.
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