P1 - Energy Transfer By Heating Flashcards
What type of energy transfer is infrared radiation?
Electromagnetic
The hotter the object the ________ infrared radiation is emitted.
More
Does infrared use particles? And give a real life use of this
No
The sun travelling through a vacuum (space) to earth
Why are houses in hot countries painted white?
White, shiny surfaces emit and absorb heat radiation less quickly than dull black surfaces
How is the arrangement of particles in a liquid different from those in a solid
Solids vibrate around a fixed point and so have a fixed shape. Liquid particles are in contact but can move freely and so doesn’t have a fixed shape and can flow.
How does conduction occur?
One end of the solid is heated, the particles gain kinetic energy and vibrate more. This energy is passed to neighbouring particles and is transferred throughout the solid.
What is conduction like in metals
When metals are heated their particles free electrons gain kinetic energy and move throughout the metal transferring energy by colliding with other particles. Hence why metals are good conductors
What is convection
When a fluid is heated it expands, becomes , less dense and rises, this is replaced by cool liquids, becomes more dense and falls, creating a flowing convection current. (Hence why it can only be in liquids and gases).
What’s evaporation
Liquid to gas
The more energetic particles gain energy and leave the liquid leaving an average lower temperature. Evaporation causes cooling
How to increase the rate of evaporation?
- increase surface area of the liquid
- breeze over the top
- increase the temperature of the liquid
What’s condensation
Gas to liquid
Takes place on cold surfaces
How to increase rate of condensation
Decrease temperature
Increase surface area
How to increase the rate of energy transfer
Increase the temperature difference between the two mediums
What does energy transfer rate depend upon other than temperature difference
The materials
The shape
The surface area
How to maximise energy transfer?
Dull Matt black surfaces
Good conductors (metals)
Explain how a vacuum flask works
Double wall with vacuum prevents conduction/convection as there’s no particles
Inside the drink the walls are silver to reflect the radiation back into the drink
Silvered outside to reduce the heat emitted from conduction and radiation
The grater the mass the more _________ it takes to heat it
Slowly
What affects the rate of temperature change in a substance?
Energy transferred to it
Mass
Specific heat capacity
What’s the specific heat capacity equation and units
E = m x c x @
E - energy transferred (Joules)
M - mass (KG)
C - specific heat capacity (sometimes 4.2) (J/kg degrees)
@ - temperature change (degrees)
Describe a few ways to minimise energy loss through the house
Fibreglass loft (good insulator, stops conduction)
Double glazing (stops convection)
Cavity wall (convection - traps air in small air bubbles)
What’s a U value?
How much energy per second is transferred
The lower the u value the better the insulator
Why is fibreglass a good insulator?
Contains trapped air
