1. Why is cooking quicker in a pressure cooker?
A. As the pressure inside the cooker increases, the boiling point of water is raised, hence, the cooking process is quicker.
2. Why are ventilators in a room always made near the roof?
A. The hot air being lighter in weight tends to rise above and escape from the ventilators at the top. This allows the cool air to come in the room to take its place.
3. Why does a balloon filled with hydrogen rise in the air?
A. Weight of hydrogen is less than the weight of air displaced by it. In balloons hydrogen is normally filled because it is lighter than air.
4. Why does smoke curl up in the air?
A. Smoke contains hot gases which being lighter in weight, follows a curved path because of the eddy currents that are set up in the air.
5. Why does an electric bulb explode when it is broken?
A. The bulb encompasses partial vacuum and as it breaks, air rushes in causing a small explosion.
6. If a lighted paper is introduced in a jar of carbon dioxide, its flame extinguishes. Why?
A. Because carbon dioxide does not help in burning. For burning, oxygen is required.
7. Why is it dangerous to have charcoal fire burning in a closed room?
A. When charcoal burns it produces carbon monoxide which is suffocating and can cause death.
8. Why is it easier to lift a heavy object under water than in air?
A. Because when a body is immersed in water, it experiences an upward thrust (Archimedes? Principle) and loses weight equal to the weight of the water displaced by its immersed potion, and hence, is easier to lift objects.
9. If a highly pumped up bicycle tyre is left in the hot sunlight, it bursts. Why?
A. The air inside the tube increases in volume when heated up. As sufficient space for the expansion of the air is not available because the tube is already highly pumped, it may result in bursting of the tyre.
10. Why are the mountains cooler than plains?
A. Air on the mountains is less dense so it absorbs less heat.
11. Which gas is essential to sustain life on earth?
A. Oxygen
12. Who discovered oxygen?
A. Joseph Priestly discovered oxygen, the colorless, odorless, gaseous chemical element forming about 20 percent of the Earth’s atmosphere in 1774.
13. Which is the lightest gas next to Hydrogen
A. Helium
14. The number of molecules contained in 1mole of a gas is called
A. Avogadro number
15. Hydrogen was discovered by
A. Cavendish
16. What continent is subjected to the world's largest ozone hole?
A. Antarctica.
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