Edexcel IGCSE Physics 复习笔记 4.1.6 Reducing Energy Loss
Edexcel IGCSE Physics 复习笔记 4.1.6 Reducing Energy Loss
Reducing Energy Loss
- Energy loss can be reduced by doing one of two things:
- By reducing the amount of unwanted (wasted) energy that is produced
- By preventing the energy from dissipating (if, for example, it has been produced deliberately)
Insulation
- In many situations, the heat that is produced is wanted. For example:
- When heating a home
- When boiling a kettle
- If this heat can be prevented from dissipating, then less thermal energy will be needed to replace the heat that has been lost
- This can be achieved by surrounding the appliance with insulation
- The effectiveness of insulation depends upon:
- How well the insulation conducts heat
- How thick the insulation is
- Insulating the loft of a house lowers its rate of cooling, meaning less heat is lost to the 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
- It has a much lower thermal conductivity than the roof material
- Several layers of insulation make it very thick and therefore decrease the rate of cooling
Less heat is lost from a building with the help of insulation (filled cavity in walls)
- Another aspect that affects the rate of energy lost as heat is through the walls
- Houses in cold countries are fitted with cavity wall insulation 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
Exam Tip
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 conductor of heat
- Trapping the air also prevents it from transferring heat by convection
- This reduces the rate of heat loss 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.
转载自savemyexam
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