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A Journey through States of Water - How can Water be Evaporated Faster or Slower?

Grade 6CBSE

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

🔑Concepts

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Evaporation is the process by which water changes from a liquid state to a gaseous state (water vapor) at any temperature below its boiling point (100∘C100^{\circ}C).

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Temperature: The rate of evaporation increases with an increase in temperature. Higher temperature provides more kinetic energy to the water molecules to escape into the air.

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Surface Area: Evaporation is a surface phenomenon. Increasing the exposed surface area increases the rate of evaporation because more molecules are exposed to the air.

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Wind Speed: Higher wind speed increases the rate of evaporation by carrying away the water vapor from the surroundings, preventing the air from becoming saturated.

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Humidity: Humidity is the amount of water vapor present in the air. If the humidity is high, the air can hold less additional water vapor, so the rate of evaporation decreases.

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Evaporation causes cooling: When water evaporates, it takes the latent heat of vaporization from the surroundings, resulting in a decrease in temperature.

📐Formulae

Rate of Evaporation∝Temperature\text{Rate of Evaporation} \propto \text{Temperature}

Rate of Evaporation∝Surface Area\text{Rate of Evaporation} \propto \text{Surface Area}

Rate of Evaporation∝Wind Speed\text{Rate of Evaporation} \propto \text{Wind Speed}

Rate of Evaporation∝1Humidity\text{Rate of Evaporation} \propto \frac{1}{\text{Humidity}}

💡Examples

Problem 1:

Two identical wet towels are hung out to dry. Towel A is folded in half, while Towel B is spread out completely. Which towel will dry faster?

Solution:

Towel B will dry faster.

Explanation:

Towel B has a larger surface area exposed to the atmosphere compared to Towel A. Since evaporation is a surface phenomenon, a larger surface area allows more water molecules to escape into the air simultaneously, thus increasing the rate of evaporation.

Problem 2:

Suppose you spill 50 ml50 \text{ ml} of water on the floor. On a rainy day, it takes 6060 minutes to dry. On a hot sunny day, it takes only 1515 minutes. Calculate the difference in drying time.

Solution:

60−1545\begin{array}{r} 60 \\ - 15 \\ \hline 45 \end{array} The difference is 4545 minutes.

Explanation:

On a sunny day, the temperature is higher. Since Rate of Evaporation∝Temperature\text{Rate of Evaporation} \propto \text{Temperature}, the water evaporates much faster than on a rainy day when the temperature is lower and humidity is higher.

Problem 3:

Why do we feel cool when we sit under a fan after sweating?

Solution:

The fan increases wind speed, which accelerates evaporation of sweat.

Explanation:

The moving air from the fan carries away the water vapor near our skin. This increases the rate of evaporation of sweat. Since evaporation requires heat, it absorbs heat from our body, causing a cooling effect.