Questions Answers For All Chapters – Geography Class 7
Air Pressure
Q. 1. Give reasons:
(1) Air pressure decreases with increasing altitude.
Answer:
- As altitude increases, the proportion of dust, water vapor, and heavy gases decreases, making the air thinner.
- The thinner air has lower density, leading to a decrease in air pressure.
- Since air pressure is the weight of the air above a certain point, it is higher at sea level and decreases as one moves upward.
(2) Pressure belts oscillate.
Answer:
- The intensity and duration of sunlight vary throughout the year due to the Earth’s revolution.
- This causes temperature zones and pressure belts to shift 5° to 7° northward in Uttarayan (summer in the Northern Hemisphere) and southward in Dakshinayan (winter in the Northern Hemisphere).
- This movement of pressure belts is called oscillation of pressure belts.
Q. 2. Give short answers to the following questions.
(1) What effect does temperature have on air pressure?
Answer: Effect of temperature on air pressure:
- Higher temperature causes air to expand, become lighter, and rise, leading to low air pressure.
- Lower temperature makes air denser and heavier, causing it to descend and create high air pressure.
(2) Why is the subpolar low pressure belt formed?
Answer: Reason for the formation of the subpolar low-pressure belt:
- Due to Earth’s curvature, the surface area between parallels decreases as we move toward the poles.
- This reduces friction and, combined with the Earth’s rotational motion, pushes air outward, forming a low-pressure belt between 55° and 65° latitude in both hemispheres.
Q. 3. Write notes on:
(1) Mid-latitudinal high pressure belts
Answer: Mid-latitudinal High-Pressure Belts:
- When warm air from the equator rises and moves towards the poles, it cools and becomes heavier at higher altitudes.
- This cold, dense air descends between 25° to 35° latitude, creating high-pressure belts.
- The air in these regions is dry, leading to low rainfall, which is why most hot deserts are found here.
(2) Horizontal distribution of air pressure.
Answer: Horizontal Distribution of Air Pressure:
- Air pressure is not uniform across the Earth and varies due to temperature, altitude, and humidity.
- It forms distinct pressure belts:
- Equatorial Low (5° N – 5° S)
- Mid-Latitudinal High (25° – 35° N & S)
- Subpolar Low (55° – 65° N & S)
- Polar High (80° – 90° N & S)
Q. 4. Fill in the gaps with the appropriate option.
(1) At higher altitudes, air becomes thinner. (thicker, thinner, hotter, more humid)
(2) Air pressure is expressed in millibars. (millibars, millimetres, millilitres, milligrams)
(3) On Earth, air pressure is uneven. (uniform, uneven, high, low)
(4) The Equatorial Low pressure belt spreads between 5° North and 5° South parallel. (Equatorial low, Polar high, Subpolar nlow, Mid-latitudinal high)
Q. 5. How does a high pressure belt get formed near 30° parallel? Why does this region have hot deserts?
Answer:
- When hot air from the equator rises and moves towards the poles, it cools down at higher altitudes.
- This cooled, heavy air descends around 30° latitude, creating high-pressure belts.
- The air here is dry, leading to low rainfall, which results in the formation of hot deserts like the Sahara, Kalahari, and Atacama.
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