Imp Questions For All Chapters – Geography Class 9th
Short Questions
1. Which water body holds the most water on Earth?
- Oceans hold the most water on Earth.
2. What process makes sea water salty over time?
- Rivers carry dissolved salts from rocks into the sea, and evaporation leaves them behind.
3. What is the surface temperature of sea water in mid-latitudes?
- It’s around 16°C in mid-latitudes.
4. Why is sea water near the poles so cold?
- Less sunlight and cold ocean currents keep it around 2°C.
5. At what depth does sea water temperature become constant?
- It becomes constant at 4°C after 2000 meters.
6. How do cold ocean currents change sea water temperature?
- They lower the temperature by bringing cold water to the surface.
7. How is salinity of sea water calculated?
- It’s the weight of dissolved salts in 1000g of water, in parts per thousand.
8. What causes high salinity near the Tropic of Cancer?
- Strong sunrays cause high evaporation, and there’s little fresh water input.
9. Why does salinity decrease in temperate zones?
- More rainfall and snowmelt from rivers lower salinity to about 33%.
10. Where do we extract salt from sea water commercially?
- Salt is extracted from salt-pans near coastal areas.
11. What makes the Dead Sea’s salinity reach 332%?
- High evaporation and low fresh water from the Jordan River make it extremely salty.
12. How does high salinity affect buoyancy in the Dead Sea?
- It increases water density, making it easy for people to float.
13. Which ocean has an average salinity of 35%?
- The Atlantic Ocean has an average salinity of 35%.
14. Name a device used to measure sea water salinity.
- A refractometer measures salinity accurately.
15. What two factors control the density of sea water?
- Temperature and salinity control its density.
16. Why does cold sea water sink below warm water?
- Cold water is denser, so it sinks under less dense warm water.
17. After what depth do temperature, salinity, and density stop changing?
- They stop changing significantly after 1000 meters.
18. How do differences in density create ocean currents?
- Dense water sinks and less dense water rises, starting currents.
19. Why is the Mediterranean Sea saltier than the Atlantic Ocean?
- It’s landlocked, with high evaporation and less fresh water, making salinity 39%.
20. What is the steady temperature of deep sea water globally?
- Deep sea water stays at 4°C worldwide after 2000 meters.
Long Questions
1. How does temperature change in sea water from the equator to the poles?
- Near the equator, sea water is warm, around 25°C, because of strong sunrays, but it gets colder toward the poles, dropping to 2°C. This happens because sunlight is weaker at the poles and cold currents cool the water.
2. Why does sea water temperature decrease with depth?
- Sunrays heat the surface, but they weaken as they go deeper, so temperature drops fast up to 2000 meters. After that, it stays at 4°C because no sunlight reaches that deep.
3. How do ocean currents affect sea water temperature?
- Warm currents, like the Gulf Stream, raise the temperature of sea water in some areas, making it hotter. Cold currents, like the Labrador Current, lower the temperature, keeping the water cooler.
4. What makes salinity high in tropical areas?
- In tropical areas (15°-35°), the sun is strong, causing lots of evaporation, which leaves more salt in the water. There’s also less rainfall and fewer rivers, so salinity rises to about 37%.
5. Why is salinity low in polar regions?
- Polar areas have very low evaporation because it’s cold, and melting snow adds lots of fresh water. This keeps salinity low, around 31%, even though the water is freezing.
6. How does salinity help ships float?
- Salinity makes sea water denser, which increases buoyancy, helping ships stay afloat easily. In very salty places like the Dead Sea, even people float because of this.
7. Why is the Dead Sea so salty?
- The Dead Sea has 332% salinity because it gets little fresh water from the Jordan River and has high evaporation in a hot, dry area. This leaves behind a huge amount of salt, making it one of the saltiest places on Earth.
8. How does temperature affect the density of sea water?
- Cold water is denser and sinks because the molecules pack closer together, while warm water is less dense and rises. Salinity also adds to density, but temperature has a bigger effect.
9. What happens to salinity, temperature, and density after 1000 meters depth?
- After 1000 meters, temperature stays at 4°C, salinity doesn’t change much, and density becomes steady. This is because sunlight, wind, and currents don’t reach that deep to affect them.
10. Why is salinity different in the Arabian Sea and Bay of Bengal?
- The Arabian Sea (35%) is saltier because it gets less river water and has more evaporation in a drier climate. The Bay of Bengal (34%) has lower salinity due to big rivers like the Ganga adding lots of fresh water.
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