Evaporation and Factors Affecting It - UNSOLVED PRACTICE SET

Q7. Define evaporation. How does it differ from boiling?

Q8. List four factors that affect the rate of evaporation and state how each affects it.

Q9. Why does evaporation cause cooling? Explain with an example.

Q10. Why do we spread wet clothes on a clothesline rather than bundling them up to dry?

Q11. Why does a desert cooler work better on a hot dry day than on a humid day?

Q12. Why does water in an earthen pot (matka) remain cooler than water in a metal container?

Q13. Explain the process of evaporation at the molecular level. Why does it occur only from the surface and at all temperatures? Discuss the factors that affect the rate of evaporation.

Q14. Explain why evaporation causes cooling. Describe at least three practical applications of this principle in daily life.

Q15. Compare and contrast evaporation and boiling. Discuss the similarities and differences in terms of temperature, location, bubble formation, and energy requirement.

Q16. A student investigates the rate of evaporation of water under different conditions:

(a) She places 50 mL of water in a shallow dish and 50 mL in a deep beaker. After 2 hours, the shallow dish has 30 mL remaining while the deep beaker has 40 mL. Calculate the rate of evaporation in each case and explain the difference.

(b) She repeats the experiment at 40°C and finds that the shallow dish loses all its water in 1 hour. Calculate the rate of evaporation and compare it with the rate at room temperature (assumed 25°C). Explain why temperature affects evaporation rate.

(c) She then places identical dishes in a closed room and an open veranda. The open dish loses water faster. Explain the role of humidity and air circulation.

Q17. The human body loses about 0.5 L of sweat per hour during moderate exercise. The latent heat of vaporization of water is 2260 J/g.

(a) Calculate the rate of heat loss from the body due to evaporation of sweat.

(b) If a person exercises for 2 hours, calculate the total heat lost.

(c) Explain why this mechanism is essential for maintaining body temperature in hot climates like India.

Q18. In your school science fair, a student creates a project on evaporation in the Indian context.

(a) She measures that 1 kg of water spread over 1 m² evaporates in 5 hours on a typical summer day in Delhi (temperature 40°C, humidity 30%). Calculate the rate of evaporation in kg/m²/hour.

(b) She then compares this with the same setup in Chennai (temperature 35°C, humidity 80%). The water takes 12 hours to evaporate. Calculate the rate and explain why evaporation is slower despite the higher humidity.

(c) The student uses the example of salt production in India (like in the Rann of Kutch). Explain how seawater is evaporated to obtain salt, and calculate how much salt can be obtained from 1000 kg of seawater containing 3.5% salt by mass.

(d) A classmate asks why farmers sometimes sprinkle water on the fields before an expected frost. Explain how this protects the crops using the concept of latent heat.

(e) In the Indian context, discuss how traditional methods of food preservation (like making papad, drying chillies, or making raisins from grapes) all depend on controlled evaporation. Explain the science behind each.