This is a comprehensive summary of energy for Grade 7 Natural Sciences. It provides in-depth explanations of each aspect of energy, including: Sources of energy, types of energy, types of energy systems, energy efficiency, calculating efficiency, heat transfer, energy transfer and heat insulation. ...
Energy
Energy Efficiency
• You cannot create or destroy energy, but we definitely use it and pay for it.
• The usefulness of the energy gets used as the energy gets dissipated as waste
heat.
• For example, the food mixer transfers the energy carried by the electric current
into the movement and sound.
• The mixer and the food also get hot.
• Only the movement is useful.
• The sound and heat are wasted energy.
• Once the food is mixed, the energy is scattered as the sound is absorbed by
the walls, making them a tiny bit hotter
• The warm food mixer gradually cools as its heat is spread into the room.
Food mixer energy use
• The height of the box represents the amount of energy that is put in
• The amount of the next box represents the amount of useful energy.
, • The width of any boxes pointing downwards represent the amount of wasted
energy.
Filament light bulbs and how efficient they are
• In an old-fashioned filament bulb, only 5 of 100 joules is useful so it is 5%
efficient
LED light bulbs and how efficient they are
• In an LED light bulb, 75 joules are useful out of 100 so it is 75% efficient.
• That is why we are no longer using filament bulbs
, CFL lamps and how efficient they are
Calculating efficiency
• Efficiency=(useful energy transferred divided by energy supplied) X 100.
• There are ways in which energy transfers can be made more efficient.
• For example, the use of lubrication can reduce friction and therefore reduce the
transfer to heat.
• The use of thermal insulation can also reduce the loss of heat.
• A house can be insulated in a variety of ways to reduce heat loss.
• Insulation can be added to the attic or loft.
• Double glazing can be used on the windows
• Draft excluders can be fitted to the doors.
• Cavity wall insulation can be used and carpets can be laid.
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