Energy resources and energy transfers Flashcards
Energy stores
Chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic, nuclear (Cannibals, Kicked Genies, Eagerly, Therefore, Monsters, Exhaled, Nicely)
Energy transfers
Mechanically, electrically, by heating, by radiation
(light and sound)
Principle of Conservation of Energy
Energy cannot be created or destroyed, it can only change from one form to another
Efficiency equation
Efficiency = useful energy output/total energy output x 100
Conduction
The process by which heat energy is transmitted through collisions between neighbouring atoms or molecules
Convention
The process by which heat is transferred by the movement of a heated fluid such as air or water
Radiation
Is energy that comes from a source and travels through space at the speed of light
The role of convection in everyday phenomena
Enables hot air balloons to rise, and also explains why it is often hotter in houses upstairs rather than downstairs
How do the emission and absorption of radiation link to surface and temperature?
- Light, shiny surfaces are good reflectors
- Dark, matt surfaces are poor reflectors
- This means that placed next to a heat source, a dark object would heat up faster than a light one
- Dark matt surfaces are also best at emitting infrared radiation. This means that a hot object with a light shiny surface will emit less infrared radiation than a dark matt object at the same temperature
- Hotter objects emit more infrared radiation per second. The type of electromagnetic radiation wave emitted also changes with temperature – the higher the temperature the higher the frequency of electromagnetic radiation wave emitted
How do thermal energy transfer in conduction, convection and radiation?
Conduction nvolves molecules transferring kinetic energy to one another through collisions.
Convection occurs when hot air rises, allowing cooler air to come in and be heated.
Thermal radiation happens when accelerated charged particles release electromagnetic radiation, which can be felt as heat.
Explain one way of reducing unwanted energy transfer
Use insulators - materials with low thermal conductivity or use thicker materials.
Work done equation
Work done = force x distance moved
W = F x d
(Work done is equal to energy transffered)
GPE equation
Gravitational potential energy = mass x gravitational field strength x height
GPE = m x g x h
Kinetic energy equation
Kinetic energy = 1/2 x mass x speed (squared)
How does the conservation of energy link between gravitational potential energy, kinetic energy and work?
In terms of a swinging pendulum: At the top of the swing, it will have its highest gravitational potential energy (as its further from the earth); but it will have its lowest kinetic energy (it slows to a stop at the top point).
At the bottom of the swing, it will have its lowest gravitational energy (as it is closer to the earth); but it will have its highest kinetic energy (it goes very quickly past the bottom point).
Remembering that work done is equal to energy transferred, we can see that as work is done that moves the pendulum upwards, kinetic energy is transferred in to gravitational potential energy. When work is done to bring the pendulum downwards, energy is transferred from GPE to KE.
The pendulum demonstrates that energy is conserved, as then energy is constantly changing between different forms. The only reason that energy is lost from the pendulum, and it slows down, is that some energy is transferred into heat or sound
