7.4 - Conduction, Convection & Radiation

• What happens to energy when an object is heated?

  It is transferred to its thermal energy store
• What are the three ways heat can be transferred?

  Conduction, convection, and radiation
• How is heat transferred in solids?

  By conduction
• How is heat transferred in fluids?

  By convection
• How is heat transferred through empty space?

  In the form of radiation
• What is the key idea behind conduction?

  Vibrating particles transfer energy to neighbors
• What happens when one end of a metal is heated?

  Energy is transferred to the kinetic energy store
• Why does conduction occur mainly in solids?

  Particles are held closely together
• Conduction primarily takes place in:

  Solids
• What is thermal conductivity?

  How well objects transfer energy by conduction
• Which materials have high thermal conductivity?

  Metals
• Why are plastics used as insulators?

  They have low thermal conductivity
• What is convection?

  Heat transfer mainly in fluids
• What happens to particles in fluids when heated?

  They gain kinetic energy and move faster
• What occurs in a convection current?

  Hot particles rise, cool particles sink
• How does a blanket reduce convection?

  It stops warm air from escaping
• What do conduction and convection have in common?

  Both involve particles gaining kinetic energy
• How can heat be transferred without particles?

  Through radiation in a vacuum
• What happens to all objects regarding radiation?

  They constantly absorb and emit radiation
• What does a hotter object do regarding radiation?

  It emits more radiation
• Why does it feel hot to put your hand over a barbecue?

  Hot metal emits infrared radiation
• What type of waves carry energy in radiation?

  Infrared waves
• What is the electromagnetic spectrum?

  A range of all types of electromagnetic radiation
• What are the processes of heat transfer?

  • Conduction: Energy transfer through particle collisions in solids
  • Convection: Energy transfer through fluid movement
  • Radiation: Energy transfer through infrared waves in a vacuum
• What are the differences between conduction and convection?

  Conduction:

  • Occurs mainly in solids
  • Involves energy transfer between particles

  
  

  Convection:

  • Occurs mainly in fluids
  • Involves movement of particles
• What happens when one end of a solid object is heated?

  Energy is transferred to kinetic energy stores
• What effect does heating have on the particles at the heated end of a solid object?

  Particles vibrate faster and collide more often
• How does the kinetic energy transfer from one particle to another in a solid object?

  Through collisions between neighboring particles
• What is the overall process of transferring heat energy in solids called?

  Conduction
• Describe the process of conduction in solids.

  • Heating one end of a solid object
  • Energy transfers to kinetic energy stores of particles
  • Particles vibrate faster and collide more often
  • Kinetic energy is passed to neighboring particles
  • Process repeats, transferring energy along the object
  • Overall, heat (thermal energy) is transferred
• Thermal conductivity is a measure of how well a material conducts energy when it is heated. 

  Which type of materials have a higher thermal conductivity? 

  Metals
• What do we mean by the term 'fluid', and which states of matter are considered fluids? 

  • Particles are free to move
  • Liquids
  • Gases
• Convection can take place in:

  • Gases
  • Liquids
• How convection works:

  • This causes the fluid to become less dense and so it will rise above any cooler fluid that hasn't been heated (because that fluid is more dense).
  • As the fluid cools down it will become more dense again, and so sink back down.
  • If this process takes place in a limited space, like a container or a room, it can create a convection current.
  • As a fluid is heated the particles gain kinetic energy and spread further apart.
• Which of the following examples help to reduce heat loss via convection:

  Covering yourself with a blanket at night 

  Making a kettle from plastic rather than metal

  Closing your windows

  • Covering yourself with a blanket at night
  • Closing your windows
• When we say heat energy is transferred by 'radiation', we are referring to:

  Infrared radiation
• Which of the following statements about infrared radiation is correct?

  It involves the movement of molecules due to a change in density

  It is a form of electromagnetic radiation

  It involves the transfer of electrons through the material

  It can travel through a vacuum

  • It is a form of electromagnetic radiation
  • It can travel through a vacuum
• Do hotter or cooler objects emit more infrared radiation?

  • Hotter
  • Hotter objects have more energy, so also emit more energy.
• Which of the following statements is correct?

  Warm fluids rise because they are less dense than cooler fluids

  Steel conducts heat because their particles rise when heated

  Convection only occurs in gases

  Warm fluids rise because they are less dense than cooler fluids