P1.1 Energy Transfer By Heating Flashcards
Define infrared radiation.
A type of electromagnetic radiation which involves waves rather than particles. It can pass through a vacuum.
All objects emit IR and the hotter the object the more IR it emits.
What surface is the best emitter and best absorber?
Matt black
What surface is the worst emitter and worst absorber?
Shiny silver
Why are solar heating panels painted black?
The panels have to absorb heat radiation as quickly as possible. Black is the best absorber of IR
Describe how particles are structured in a solid.
The particles are in a structured position and are very dense and won’t flow. The particles vibrate but stay in a fixed position.
Describe how particles are structured in a liquid.
The particles aren’t fixed and are in a random position. They flow easily and have a lower density than a solid but a higher density than a gas.
Describe how particles are structured in a gas.
The particles are completely random and free to flow anywhere. The density in very low. You can’t see the particles flowing but they’re quite fast. They are not in a fixed position.
How does conduction happen in non metals?
The particles are heated and they vibrate and collide with neighbouring particles. The heat energy is then slowly passed on.
Why are metals good conductors?
Free electrons
These can move throughout the solid and collide with more particles.
What’s a fluid? How is heat energy transferred in a fluid?
A fluid is a liquid or gas.
The heated fluid particles gain energy so they move about more and spread out. The same number of particles now take up more space so the fluid has become less dense.
Why is a liquid cooler after evaporation?
Weak attractive forces exist between the molecules in the liquid. The faster molecules, which have more kinetic energy, break away from the attraction of the other molecules and escape from the liquid. After they leave, the liquid is cooler because the average kinetic energy of the remaining molecules in the liquid has decreased.
The rate at which an object transfers energy by heating depends on……..
Surface area
Volume
Material
Temperature difference
How does a vacuum flask limit heat transfer?
Silvered surfaces reflect heat back into the liquid
The vacuum limits evaporation, convection and conduction
The plastic cork stops evaporation and convection
Metal casing is a good conductor so heat outside can transfer in
What’s in double glazed windows that limit heat transfer?
Vacuum between the two panes
How does loft insulation stop heat transfer?
Stops the heat energy rising out of the house. Insulation limits convection and conduction.
How do draught excluder doors stop heat transfer?
Stops convection
Warm air is trapped in the house
How does carpet stop heat transfer?
Stops conduction
Cold heat energy can’t be transferred from underneath to the house
How does cavity wall insulation stop heat transfer?
Stops conduction and convection.
Between the bricks and wall there might be a vacuum. Heat energy is trapped in the room. The wall isn’t a good conductor
How do curtains stop heat transfer?
Stops convection
The air between the window and curtain is trapped. Stops heat energy passing out through windows
How do radiator reflectors stop heat transfer?
Stops radiation. Reflects the heat energy back into the radiator and then back to your room
What’s a U-value?
The measure of heat energy transfer.
The more heat energy transferred, the higher the U-value.
The lower the U-value, the better the material is as an insulator.
What measures the insulation on a duvet?
Tog rating
The higher the rating the more insulating
How do you calculate specific heat capacity?
Energy / (mass X temperature difference)
What is specific heat capacity?
The energy needed to raise the temperature of a 1 kg mass by 1 degrees c
What’s the unit of specific heat capacity?
J/kg degrees c
What’s payback time?
The time it takes for the cost of installing insulation to be equalled by the savings made from reduced energy costs.
How do you calculate payback time?
Cost of insulation / saving each year
Silver reflectors cost £25 and saves £50 per year. What’s the payback time?
25/50
0.5 years or 6 months
Why do people still install double glazed windows even if the payback time is soooo long?
Because it looks nicer and is safer.
