krit.club logo

Heat Transfer in Nature - Water Cycle

Grade 7CBSE

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

🔑Concepts

•

Radiation is the primary mode of heat transfer from the Sun to the Earth's surface, providing the energy required to drive the water cycle without the need for a material medium.

•

Evaporation occurs when liquid water in oceans and lakes absorbs thermal energy (QQ), causing molecules to move faster and escape into the atmosphere as water vapor.

•

Convection is responsible for the rising of warm, moist air. As air heats up, its volume increases and its density decreases (Density=MassVolumeDensity = \frac{Mass}{Volume}), causing it to rise.

•

Condensation is the process where water vapor rises to cooler altitudes, loses heat energy to the surroundings, and transforms back into liquid water droplets to form clouds.

•

Advection and convection currents move clouds across different regions, eventually leading to Precipitation (rain or snow) when droplets become too heavy.

•

Sea Breeze and Land Breeze are localized convection currents. During the day, land heats up faster than water, causing air above land to rise and cooler air from the sea to blow towards the land.

📐Formulae

Celsius to Fahrenheit: C5=F−329\text{Celsius to Fahrenheit: } \frac{C}{5} = \frac{F - 32}{9}

Density of Air: ρ=mV\text{Density of Air: } \rho = \frac{m}{V}

Phase Change (Evaporation): Liquid+Heat→Vapor\text{Phase Change (Evaporation): } Liquid + Heat \rightarrow Vapor

Phase Change (Condensation): Vapor→Liquid+Heat\text{Phase Change (Condensation): } Vapor \rightarrow Liquid + Heat

💡Examples

Problem 1:

During a hot summer day, the temperature of a coastal area is recorded as 35∘C35^\circ C. Convert this temperature to the Fahrenheit scale to understand the heat intensity affecting evaporation.

Solution:

Using the formula C5=F−329\frac{C}{5} = \frac{F - 32}{9}:

Step 1: Substitute C=35C = 35 355=F−329\frac{35}{5} = \frac{F - 32}{9}

Step 2: Simplify the fraction 7=F−3297 = \frac{F - 32}{9}

Step 3: Multiply both sides by 99 7×9=F−327 \times 9 = F - 32 63=F−3263 = F - 32

Step 4: Solve for FF F=63+32F = 63 + 32 F=95∘FF = 95^\circ F

Explanation:

The temperature of 35∘C35^\circ C is equivalent to 95∘F95^\circ F, which provides sufficient thermal energy for significant evaporation from the ocean surface.

Problem 2:

Calculate the difference in temperature of a water body if it was 22∘C22^\circ C in the morning and rose to 38∘C38^\circ C by noon due to solar radiation.

Solution:

To find the temperature increase, we subtract the initial temperature from the final temperature:

38−2216\begin{array}{r} 38 \\ - 22 \\ \hline 16 \end{array}

The temperature difference is 16∘C16^\circ C.

Explanation:

A rise in temperature indicates that the water has absorbed heat via radiation, increasing the kinetic energy of the water molecules.