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Unit 1: Energy
1.2 Conservation and Dissipation of Energy
1.2.2 Efficiency of Energy Transfers
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What is efficiency a measure of?
Energy conversion effectiveness
Efficiency is calculated as the useful output energy divided by the total input energy and then multiplied by
100%
In an energy transfer with 75% efficiency,
25%
of the energy is dissipated as waste.
What is the principle of energy conservation?
Energy cannot be created or destroyed
Energy dissipation often results in the production of heat or
sound
What are the key points of energy conservation?
Neither created nor destroyed
High friction leads to high energy efficiency.
False
What is the formula for calculating energy transfer efficiency?
Useful Output Energy
Total Input Energy
×
100
%
\frac{\text{Useful Output Energy}}{\text{Total Input Energy}} \times 100\%
Total Input Energy
Useful Output Energy
×
100%
If a system has a total input energy of 300 J and a useful output energy of 210 J, its efficiency is
70%
Order the following examples from highest to lowest efficiency:
1️⃣ LED Bulbs (90%)
2️⃣ Energy Star Appliances (80%)
3️⃣ High-Insulation Homes (75%)
4️⃣ Hybrid Cars (50%)
LED bulbs are more energy-efficient than
incandescent
bulbs.