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Earth as a System: Energy, Matter and Life - Explain wind formation, land/sea breezes, and role of atmosphere in weather

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The atmosphere acts as a protective blanket, keeping the average temperature of the Earth fairly steady during the day and even during the course of the whole year.

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Air movement (Wind) is caused by the uneven heating of the atmosphere by the sun. As air gets heated, its density decreases (ρ∝1T\rho \propto \frac{1}{T}), causing it to rise and create a region of low pressure.

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Wind flows from regions of high pressure to regions of low pressure to equalize the atmospheric imbalance.

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Sea Breeze: During the day, land heats up faster than water. The air over land rises, creating low pressure. Cooler air from the sea moves towards the land.

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Land Breeze: At night, land cools down faster than water. The air over the sea is warmer and rises, creating low pressure over the water. Cooler air from the land moves towards the sea.

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Role of the Atmosphere: It prevents the sudden increase in temperature during daylight and slows down the escape of heat into outer space during the night. It also contains gases like CO2CO_2 and water vapor that contribute to the greenhouse effect.

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Weather vs. Climate: Weather describes the short-term state of the atmosphere (e.g., rain, wind, temperature), while climate is the average weather pattern over a long period (usually 30 years).

📐Formulae

P=FAP = \frac{F}{A}

ρ=mV\rho = \frac{m}{V}

Q=mcΔTQ = mc\Delta T

P∝T (at constant volume)P \propto T \text{ (at constant volume)}

💡Examples

Problem 1:

During a sunny day at the coast, the temperature of the land is 35∘C35^\circ C and the temperature of the sea is 25∘C25^\circ C. Explain the direction of air movement and the pressure conditions.

Solution:

  1. Land Temperature (TlandT_{land}) = 35∘C35^\circ C. 2. Sea Temperature (TseaT_{sea}) = 25∘C25^\circ C. Since Tland>TseaT_{land} > T_{sea}, air above the land expands and rises, creating a Low Pressure area (PlowP_{low}). The air above the sea is cooler and denser, creating a High Pressure area (PhighP_{high}).

Explanation:

Wind always moves from high pressure to low pressure. Therefore, air moves from the sea to the land, forming a 'Sea Breeze' during the day.

Problem 2:

Calculate the pressure exerted by a column of air if it applies a force of 101325 N101325\ N over an area of 1 m21\ m^2.

Solution:

P=FA=1013251=101325 PaP = \frac{F}{A} = \frac{101325}{1} = 101325\ Pa

Explanation:

Using the formula for pressure P=FAP = \frac{F}{A}, where FF is the force in Newtons and AA is the area in square meters, we find the atmospheric pressure at sea level is approximately 1.013×105 Pa1.013 \times 10^5\ Pa.