Energy Transfers
Visão Geral
Every device you use - from a phone charger to a car engine - takes energy in one form and transforms it into something useful, but none of them manages to convert all of it. Understanding where that energy goes, and how much of it actually does what you want, is one of the most practical ideas in all of physics.
In this lesson you will learn the eight energy stores that physicists use to describe where energy sits, the four transfer pathways it moves along, and why the total never changes. You will calculate efficiency, read Sankey diagrams, and explore how heat travels by conduction, convection and radiation - skills that Edexcel tests across Papers 1 and 2 every session.
Objetivos
- Describe energy transfers involving energy stores: chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear; and energy transfers: mechanically, electrically, by heating, by radiation (light and sound)
- Use the principle of conservation of energy
- Know and use the relationship between efficiency, useful energy output and total energy output: efficiency = useful energy output / total energy output x 100%
- Describe a variety of everyday and scientific devices and situations, explaining the transfer of the input energy, including their representation by Sankey diagrams
- Describe how thermal energy transfer may take place by conduction, convection and radiation
- Explain the role of convection in everyday phenomena
- Explain how emission and absorption of radiation are related to surface and temperature
- Investigate thermal energy transfer by conduction, convection and radiation
- Explain ways of reducing unwanted energy transfer, such as insulation
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- Which of the following is NOT an energy store? A) Chemical B) Kinetic C) Electrical D) Nuclear Answer: C
- A lamp converts 100 J of electrical energy. 20 J is transferred to light and 80 J to heat. What is the efficiency? A) 80% B) 20% C) 25% D) 100% Answer: B
- Which thermal transfer mechanism can work through a vacuum? A) Conduction B) Convection C) Radiation D) All three Answer: C
- In a Sankey diagram, what does the width of an arrow represent? A) The speed of energy transfer B) The amount of energy C) The temperature D) The type of energy Answer: B
- Cavity wall insulation reduces heat loss mainly by preventing: A) Radiation through the walls B) Conduction through the bricks C) Convection currents in the air gap D) Sound transfer Answer: C
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