Reducing Energy Loss (Edexcel IGCSE Physics)

Revision Note

Katie M

Author

Katie M

Last updated

Reducing energy loss

  • There are many situations where energy transfers are actually unwanted:

    • Keeping a house warm

    • Keeping a drink hot or cold

    • Dressing to stay warm in cold weather

insulated-cup-new

Insulated mugs are used to maintain the temperature of hot or cold drinks

 

  • When an appliance is used for heating something (a kettle, a heater, a tumble dryer, a central heating system, etc.), the appliance requires a lot of energy

    • It can become expensive for a household to run such appliances

    • The production of electricity using fossil fuels produces greenhouse gases, which contribute to global warming

    • The combustion of (methane) gas produces greenhouse gases, which contribute to global warming

  • Therefore, it is often useful to explore ways of reducing unwanted energy transfers

  • Energy that is dissipated to the surroundings is often the main source of wasted energy transfers

  • If these unwanted energy transfers can be prevented, or reduced, the useful energy transfers can be made more efficient

Reducing conduction

  • Energy transfers by heating due to conduction are one of the most common sources of dissipated energy

  • To reduce energy transfers by conduction, materials with a low thermal conductivity should be used

    • Materials with low thermal conduction are called insulators

 

Reducing convection

  • Convection can also be a source of dissipated energy 

  • To reduce energy transfers by convection, convection currents must be prevented from forming

  • Therefore, the fluid (liquid or gas) that forms the currents must be prevented from moving

 

Insulation

  • Insulation reduces energy transfers from both conduction and convection

  • The effectiveness of an insulator is dependent upon:

    • The thermal conductivity of the material

      • The lower the conductivity, the less energy is transferred 

     

    • The density of the material

      • The more dense the insulator, the more conduction can occur

      • In a denser material, the particles are closer together so they can transfer energy to one another more easily

     

    • The thickness of the material

      • The thicker the material, the better it will insulate

  • Insulating the loft of a house lowers its rate of cooling, meaning less energy is transferred to the surroundings (outside)

  • The insulation is often made from fibreglass (or glass fibre)

    • This is a reinforced plastic material composed of woven material with glass fibres laid across and held together

    • The air trapped between the fibres makes it a good insulator

  • The gaps or cavities between external walls are often filled with insulation

    • This is called cavity wall insulation

    • This is often done by drilling a hole through the external wall to reach the cavity and filling it with a special type of foam which is made from blown mineral fibre filled with gas

    • This lowers the conduction of heat through the walls from the inside to the outside

Cavity insulation

Cavity Wall Insulation, downloadable IGCSE & GCSE Physics revision notes

Less energy is transferred by conduction and convection if the cavity is insulated

Examiner Tips and Tricks

A common mistake when explaining how an insulator keeps something warm is to state something along the lines of “The object warms up the insulator which then warms the object up”.

Avoid giving this kind of answer!

The real explanation is:

  • The insulator contains trapped air, which is a poor thermal conductor

  • Trapping the air also prevents it from transferring energy by convection

  • This reduces the rate of energy transfer from the object, meaning that it will stay warmer for longer

Other things to watch out for:

  • Heat does not rise (only hot gases or liquids rise)

  • Shiny things do not reflect heat (they reflect thermal radiation)

  • Black things do not absorb heat (they absorb thermal radiation)

And remember, a good answer will often include references to more than one method of thermal energy transfer.

You've read 0 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.