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7.4Physics 01. Forces And Energy

Thermal energy transfers hot to cold heat dissipation conduction… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 11 parts Lesson 5 of 12 1 quiz

📚 Cambridge Checkpoint Science 0893 Hub / Topical Revision
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Lesson summary

7.4 Thermal energy transfer: conduction, convection and radiation — CHECKPOINT - Lower Secondary Science 0893 notes: Describe how thermal energy transfers from hot to cold and how conduction, convection and radiation transfer it and dissipate heat.Hotter to colder — thermal energ…

  • Feeling cold
  • Heat dissipation
  • Liquids and gases
  • Poor conductors
  • Not possible
  • Convection current

Part 1 of 9Direction of transfer

Hotter to colder
  • Hotter to colder thermal energy always moves from hotter places to colder places.
  • Examples are a hot drink warming hands and food cooling in a refrigerator.
Feeling cold
  • Feeling cold ice feels cold because thermal energy moves from the hand to the ice.
Heat dissipation
  • Heat dissipation thermal energy spreads out from a hotter object to cooler surroundings.
  • The rate rises as the temperature difference rises.

Part 2 of 9Particles and heating

Particles and heating
Solids
  • Solids particles vibrate more vigorously and take up more space, so solids expand.
Liquids and gases
  • Liquids and gases particles move faster and take up more space, so they expand.

Part 3 of 9Conduction

Conduction
  • Conduction transfer of thermal energy by vibrating particles passing vibrations to the particles next to them.
  • It works best in solids, where particles are close together.
  • Metals are the best conductors because free electrons help pass on the energy.
Poor conductors
  • Poor conductors plastics, wood and fabrics are thermal insulators.
Not possible
  • Not possible conduction is poor in liquids and gases and cannot happen in a vacuum.

Part 4 of 9Convection

Convection
  • Convection transfer of thermal energy by the movement of heated liquid or gas.
  • Heated fluid expands and becomes less dense, so it rises.
  • Colder, denser fluid sinks to take its place.
Convection current
  • Convection current the circulation that heats all the liquid or gas.
Not possible
  • Not possible convection cannot happen in solids or a vacuum.

Part 5 of 9Radiation

Radiation
  • Radiation transfer of thermal energy by waves that do not need particles.
  • It passes through a vacuum, which is how the Sun's energy reaches Earth in about nine minutes.
Emitters and absorbers
  • Emitters and absorbers all objects emit radiation and hotter objects emit more.

Part 6 of 9Surfaces and radiation

SurfaceEmits and absorbs radiation
Dull, black, large areaBest
Shiny, white or silver, small areaWorst, and reflects radiation

Part 7 of 9Comparison of the three methods

MethodNeeds particlesOccurs in
ConductionYesSolids mainly
ConvectionYesLiquids and gases
RadiationNoThrough vacuum and transparent materials

Part 8 of 9Cooling by evaporation

Evaporation
  • Evaporation liquid particles with the most energy escape from the surface as a gas.
  • The average energy of the particles left behind decreases.
  • So the temperature of the remaining liquid falls and it cools.
Thermal energy
  • Thermal energy the escaping particles take thermal energy away from the liquid and its surroundings.
Examples
  • Examples sweat evaporating from the skin cools the body, and a swimmer feels cold on leaving the pool.
Faster evaporation
  • Faster evaporation a warmer liquid, a larger surface area and moving air all increase evaporation.

Part 9 of 9Reducing thermal energy transfer

Vacuum flask
  • Vacuum flask a silvered, double-walled bottle with a vacuum between the walls reduces conduction and radiation.
Double glazing
  • Double glazing two layers of glass with argon between them reduce conduction.
Cavity wall foam
  • Cavity wall foam a poor conductor that also stops convection currents.
Clothes
  • Clothes insulating materials slow the conduction of thermal energy away from the body.

Key terms

TermMeaning
ConductionThermal energy transfer by particles vibrating in a solid.
ConvectionThermal energy transfer by moving liquid or gas.
RadiationThermal energy transfer by waves, with no particles needed.
InsulatorA poor conductor of thermal energy.
Convection currentCirculation of heated and cooled fluid.

Avoid these mistakes

1
Cold moves from ice into the hand — thermal energy moves from the hand into the ice.
2
Conduction happens in a vacuum — it needs particles.
3
Hot air rises because heat rises — hot air is less dense so it rises.
4
Radiation needs a medium — radiation travels through a vacuum.

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