iGCSE Physics (0625) 2.2.3 Melting, boiling and evaporation Paper 4 -Exam Style Questions- New Syllabus
Question
(i) Describe how evaporation from the puddle occurs. Use ideas about particles in your answer.
(ii) State and explain one change in the weather that causes a faster rate of evaporation.
Most-appropriate topic codes (Cambridge IGCSE Physics 0625):
• Topic $2.2.3$ — Melting, boiling and evaporation (Part $\mathrm{(a)}$)
• Topic $1.5.1$ — Effects of forces (Part $\mathrm{(b)}$)
▶️ Answer/Explanation
(a)(i)
For the correct answer:
Energetic particles escape from the surface of the liquid.
Evaporation occurs because particles within a liquid have a distribution of kinetic energies. The most energetic (fastest-moving) particles near the surface can overcome the attractive intermolecular forces exerted by neighboring particles. Once these high-energy particles break free, they escape into the air as a gas (vapor), leaving behind particles with a lower average kinetic energy.
(a)(ii)
For the correct answer:
Increase in temperature (or increase in wind speed / Sun shining).
An increase in temperature provides the water particles with more thermal energy, which increases their average kinetic energy. This results in a higher proportion of particles having enough energy to escape the surface. Alternatively, wind increases the rate by blowing away the newly evaporated vapor, preventing particles from returning to the liquid.
(b)
For the correct answer:
Braking distance increases because friction decreases.
When the road is wet, a layer of water acts as a lubricant between the car tires and the road surface, significantly reducing the friction. Since the frictional force is the primary force responsible for decelerating the car, a lower friction force means it takes much longer to dissipate the car’s kinetic energy, resulting in a greater braking distance.