Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

12.6Chapter 12: Energy Transfer

Cooling by evaporation — Alhussan Physics - Stage 9 Revision Notes & Topical Questions

5 min read 8 parts Lesson 6 of 7 2 quizzes

📚 Alhussan Physics - Stage 9 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

Physics 12.6 Cooling by evaporation — Particle Kinetic Energy Distribution and Latent Cooling — Alhussan International Academy — Physics (Stages 7–9) notes: Explain why liquids cool when they evaporate and describe uses of cooling by evaporation.Evaporation = a liquid changing to…

  • Everyday example
  • Different from boiling
  • Particles in a liquid
  • Range of speeds
  • Continued evaporation
  • Average height model

Part 1 of 6Evaporation

Evaporation
Evaporation a liquid changing to a vapour at its surface at any temperature.
Everyday example
  • A dish of water left out dries up.
Different from boiling
  • It happens only at the surface and at any temperature.

Part 2 of 6Particle explanation of cooling

Particle explanation of cooling
Particles in a liquid
  • They are close together, move over each other and attract their neighbours.
Range of speeds
  • Particles move in all directions at different speeds, and the average speed depends on the temperature.
  • At a higher temperature the average speed is higher.
  • Energy is transferred between particles in collisions.
Escape
  • A few fast particles at the surface have enough kinetic energy to overcome the attraction of neighbours and escape into the air.
Cooling
  • The slower particles left behind lower the average speed, so the liquid is cooler.
Continued evaporation
  • The cooler liquid absorbs energy from the air or skin around it, so more particles escape and the air around cools.

Part 3 of 6A model for evaporative cooling

A model for evaporative cooling
Average height model
  • The average height of a group falls when the tallest children leave.
Particles
  • When the fastest particles leave a liquid, the average speed of the remaining particles falls.

Part 4 of 6What makes evaporation faster

Warmer liquid or air
  • More particles have enough energy to escape.
Larger surface area
  • More particles are at the surface.
Moving air
  • It carries vapour away.
Dry air
  • Vapour can enter the air easily.

Part 5 of 6Cooling animals and people

Sweating
  • Droplets of sweat on the skin evaporate as energy is transferred from the skin to the water, so you feel cooler.
Wet hands
  • The same cooling effect happens as water dries from them.
Dogs
  • They pant so that water evaporates from their tongues.
Elephants
  • They use water on their skin to cool down.

Part 6 of 6Coolers and refrigerators

1Evaporative cooler
  • A fan draws warm air over water, energy is transferred to the water, which evaporates, and the cooled air circulates around the house.
  • It needs electricity for the fan and pump.
  • In ancient Egypt, wet mats were hung over doorways and fans cooled the air.
2Refrigerator
  • A refrigerant liquid is pumped around tubes at the back.
3Cooling inside
  • Energy from inside the refrigerator evaporates the refrigerant, which cools the inside.
4Cycle
  • The vapour is compressed and cooled outside, where it condenses and releases energy.

Key terms

TermMeaning
EvaporationA liquid changing to a vapour at its surface.
Average speedThe mean speed of the particles, related to temperature.
RefrigerantA special liquid that evaporates to cool the inside of a refrigerator.
Evaporative coolerA device that cools air by evaporating water.
VapourA gas formed from a liquid.

Avoid these mistakes

1
Thinking all particles in a liquid move at the same speed — there is a range of speeds.
2
Thinking the slowest particles evaporate — the fastest particles escape.
3
Thinking evaporation happens only at the boiling point — it occurs at any temperature.
4
Thinking evaporation warms the liquid — it cools the liquid left behind.

?What do you want to solve now?

Practice questionsTraining questions with instant feedback - not an exam. Official exam - gradedCheckpoint Quiz in MasterStudy: your mark is saved to your progress.

Last updated: