Flashcards in Energy Deck (27):
Name the energy types
Thermal, light, sound, kinetic, electricity, nuclear, chemical, GPE and Elastic potential.
What is thermal energy?
The energy possessed by hot objects, caused by the random motions of the particles in them
What is light energy?
The energy emitted by luminous objects
What is electrical energy?
The energy carried round an electrical circuits by charged particles
What is sound energy?
The energy carried by longitudinal waves from vibrating objects
What is kinetic energy?
The energy possessed by any moving object
What is chemical energy?
The energy contained in the bonds between atoms, which can be released in chemical reactions
What is nuclear energy?
The energy contained inside atomic nuclei, which can be released by certain nuclear chemical processes
What is elastic potential energy?
The energy that a stretched or squashed object possesses
What is gravitational potential energy?
The energy that an object possesses by virtue of having been lifted up in a gravitational field
What is the law of the conservation of energy?
Energy cannot be created or destroyed it can only been transferred from one form to another
How do you draw Sankey diagrams?
1. The energy is shown by arrows whose width is proportional to the amount of energy involved
2. The useful energy is drawn horizontally
3. The waster energy must be drawn pointing downwards
4. The energy input and all energy output must be labelled with energy type and the value given in Joules (J)
How do you work out efficiency?
useful energy transferred / total energy input to the system x 100
What is thermal conduction?
Thermal conduction is the transfer of thermal energy through a substance without the substance itself moving
Describe thermal conduction
1. Non-metal: the carbon atoms near the source begin to vibrate. These pass on the vibrations onto the adjacent atoms, making them vibrate, and so on along the rod. Therefore heat energy is transferred across a non-metal
2. Metal: as the copper rod is heated the copper atoms pass on energy as in non-metals. However the electrons also gain energy but unlike the atoms they are free to move around. This allows them to spread the heat energy further away heating the copper rod much faster
What are poor conductors of heat?
non-metal solids, liquids and gases
What is convection?
-Convection is the transfer of heat through fluids (gases and liquids) by the upward movement of warmer less dense regions of fluid
-Convection currents are all about changes in density
-Convection cannot happen in solids as the particles cannot move (only vibrate)
-The radiator example: as heating a room with a radiator relies on convection current, hot, less dense air by the radiator rises and denser, cooler sir floes to replace it
E.G. Hot water tanks, immersion heater in kettles
Describe a convection current
1. When a fluid is heated, their particles gain more kinetic energy and so move around more so that the average distance between the particles increase
2. This means that the fluid expands and so becomes less dense
3. Therefore the fluid rises to the top of the container
4. Here it will displace the cooler fluid which is more dense and so sinks to the bottom of the container
5. That cooler fluid will become heated and expand and rise whilst the warmer fluid with cool, and become more dense causing it to sink, creating a convection current
What is thermal radiation?
Thermal radiation is the transfer of (heat) energy by infra-red waves
E.G. Bathroom heater, army and emergency services use thermal imaging cameras
Can travel through a vacuum and at the speed of light, this is important so that we can receive heat and light from the Sun
Describe absorbers and reflectors of thermal radiation
-Highly polished, shiny surfaces and white surfaces reflect IR waves
-Matt black, dark surfaces are good absorbers of IR waves
-If something is a good reflector of IR it is a bad radiator of IR
(E.G. Hot object with shiny surface will emit less heat energy in the form of IR than another object at the same temperature with a dull black surface, keeps kettle warmer for longer, heat sink is black to stop the transistor overheating
How are the walls and roof insulation of a house energy efficient?
-Outer bricks: strong, good weathering and good insulating properties
-Thermal bricks: light, relatively cheap, very good insulating properties
-Cavity in wall: air is an insulator so stops heat transfer by conduction
-Glass fibre cavity: stops convection currents from being set up and transferring heat energy to the surroundings
-Panels may be surfaced with aluminium: highly reflective and so stops heat transfer by IR radiation
How are the windows of a house energy efficient?
-Double glazing: glass is poor thermal conductor so used in thin layers to act as insulation. Very cold countries use triple glazing
How is the loft of a house energy efficient?
-Thick layer of fibreglass is laid out across the loft floor and ceiling which reduces heat loss from the house by convection and conduction
How are the doors of a house energy efficient?
-Draught proofing: strips of foam and plastic around door and window to stop draughts of cold air blowing in and so reduces heat loss by convection
How are people insulated?
-Clothes trap air around the body, which is a poor conductor and cannot circulate, thus reducing heat loss by convection and conduction
-Clothes may also absorb some of the heat radiated out by out bodies and so reduces heat loss by thermal radiation
-In the cold, the hairs on your skin 'stand up' to trap a thick layer of insulating air around the body, this limits the amount of heat loss by convection
-Mountain climbers and marathon runners are wrapped in a thin, highly reflective blanket. The interior reflective surface, reflects heat back to their bodies which reduces heat loss by radiation, while the outer reflective surface is a poor radiator of heat
How are animals insulated?
-Birds fluff up their feathers on a cold day to increase the thickness of the air layer around their bodies and so reduces heat loss by conduction
-Penguins huddle together, so that less heat it transferred by conduction into the surrounding, so that penguins are able to keep warmer for longer as it minimises the surface area of their body exposed to the cold.