Energy transfer
Heat energy can be transferred by conduction, convection and radiation.
Dark, matt surfaces are better at absorbing heat and radiating heat than light shiny surfaces.
Light surfaces are better at reflecting heat.
Heat is emitted as infrared radiation. The hotter an object, the more infrared energy it radiates.
This is a type of electromagnetic radiation so it is waves.
This allows infrared to pass through a vacuum.
Kinetic theory
Particles in solids, liquid and gases have different amounts of energy. They are arranged differently as well.
Solids have particles close together which vibrate at a fixed position.
Liquids have particles close together but they move around each other.
Gases have particles far apart and they move quickly in random directions.
Solids have a fixed shape and cannot flow as the particles cannot move
They cannot be compressed as particles are close together and have no space to move into.
Liquids flow and take the shape of the container as they can move around each other
Liquids cannot be compressed as particles are close together and have no space to move.
Gases flows and fills the container they are put in as they can move around quickly in all directions.
They can be compressed as there are a lot of space between particles.
Conduction
Heat energy can be transferred through conduction.
Metals are good conductors but Non Metals and gases are usually insulators.
Heat energy is transferred from hot to cold.
When an object is heated, particles close to the flame get kinetic energy and vibrate more quickly.
They bump into other particles next to them and transfers the energy across. The energy is spread through the material.
In metals electrons are free to move around.
This allows them to pick up energy and collide with ions as the move throughout the structure which transfers the heat energy from one point to another.
Convection
Liquids and gases can transfer heat energy through convection.
Convection happens when a liquid or gas is heated they expand.
This is because the particles have more kinetic energy and move faster resulting in the particles taking up more volume as the gaps between particle increases.
The liquid or gas in hot areas are less dense than cold areas as they are expanded.
The denser cooler liquid or gas displaces the warm liquid or gas where it is heated by the source repeating the process.
Eventually the heat is transferred throughout the room.
Evaporation
This is when a liquid change to a gas as it is heated.
A liquid e.g. water, have particles with different energies, some of it will have enough energy to escape the liquid as a gas.
The gas leaves the liquid which brings heat energy away from the liquid. The particles left in the liquid have a lower average kinetic energy than before so the liquid cools
Condensation
Particles in a gas have different energies, some will not have enough energy to remain a gas, they will come closer together and form bonds between them releasing energy.
Condensation increase when temperature decreases
Evaporation increase when temperature increases
More surface area of the liquid and air flow also increase the rate of evaporation of a liquid
A bigger difference in temperature between the objects and the surroundings, the faster heat energy is transferred. Other factors include:
Surface area and volume
Material of object
Nature of the surface the object is touching
Animals are adapted to their surroundings
in hot climates, animals like mice have a large surface area to volume ratio.
They lose heat quickly so they don't over heat but they need to eat alot of food to replace the energy lost
Elephants have a small surface area to volume ratio, they lose heat slowly so they have problems with overheating.
Elephants have large ears to radiate heat to the surroundings.
Arctic fox has smaller ears to reduce surface area to volume ratios.
Engineering design
Car radiators are flat with many fins to provide a large surface area.
U-values
This measures the efficiency of a material as an insulator
Solar panels use heat from the sun to provide hot water or to heat up buildings.
Specific heat capacity calculates the energy required to heat up a substance.
A lower U value shows a better insulator
A high U value shows a better conductor.
Payback time
Payback time (years) = cost of installation / saving per hear
Solar panels
Solar panels heat up water but does not generate electricity.
They receive heat energy from the sun and transferred to cold water that is pumped up from a storage tank.
The water heats up and moves back into the storage tank.
Solar energy is renewable
No pollutant gas
They may produce very hot water in sunny climate. In cooler areas, a conventional boiler may be needed.
Warm water cannot be produced at night,
Specific heat capacity
E = m * c * θ
Energy (J) = Mass(kg) * Specific heat capacity (J/kg) * Change in temperature (°C)
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