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Physics 8463 - 4.1 Energy

4.1.2 Conservation and dissipation of energy

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4.1.2.1 Energy transfers in a system

Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed.

 

You should be able to describe with examples where there are energy transfers in a closed system, that there is no net change to the total energy.

You should be able to describe, with examples, how in all system changes energy is dissipated, so that it is stored in less useful ways.

This energy is often described as being 'wasted'.

You should be able to explain ways of reducing unwanted energy transfers, for example through lubrication and the use of thermal insulation.

The higher the thermal conductivity of a material the higher the rate of energy transfer by conduction across the material.

You should be able to describe how the rate of cooling of a building is affected by the thickness and thermal conductivity of its walls.

- you did heat and temperature in lower school - revise it!

- you do not have to 'do' U-values but they relate to this (and everyday life) - see my link page.

You do not need to know a formal definition of thermal conductivity - just understand what it is. They suggest you investigate thermal conductivity using rods of different materials - you did this at KS3.

Required practical activity 2:

An iinvestigation into the effectiveness of different materials as thermal insulators and the factors that may affect the thermal insulation properties of a material.

See Energy Types and Conservation of Energy

 

Cavity walls

 

Double glazing

 

Useful sample questions

 

More useful questions
4.1.2.2 Efficiency

The energy efficiency for any energy transfer can be calculated using the equation:

efficiency = (useful output energy transfer)/(total input energy transfer

Efficiency may also be calculated using the equation:

efficiency = (useful power output)/(total power input)

You may be required to calculate or use efficiency
values as a decimal or as a percentage.

  
You should be able to describe ways to increase the
efficiency of an intended energy transfer.		 HT Only