Energy Tranfer By Heating Flashcards
Do all objects emit infra red
Yes
How can we detect infrared radiation
It feels warm
How does the temp of an object affect the rate of infrared emission
The hotter the object is the more infrared it emits at any one given time
What is a vacuum
A region that doesn’t contain anything at all, not even gas particles.
Can infrared travel through a vacuum
Yes
Does the transfer of infrared involve particles
No particles are not needed
What are the best absorbers
Dark, matt surfaces
Why are houses in hot countries painted white
So the houses absorb less heat and are therefore cooler
What is meant by dull, matt surfaces are good emitters
An object painted matt black will transfer energy and cool down quickly
Why are pipes on a fridge painted black
Black surfaces are the best emitters of infrared so they will cool down quickly
What surfaces are good reflectors
Shiny surfaces
How is the arrangement of particles in a liquid different to those in a solid
In a liquid the particles are in contact with each other but are not held in fixed positions, like solids
How is the arrangement of particles in a gas different to those in a liquid
The particles in a gas are much further away and move faster than those in a liquid
Is the density of a gas much less or much more than a solid or liquid
Much less
Which two states make poor conductors
Gas and liquid
How is heat transferred through a solid
One end of the solid is heated, the particles gain kinetic energy and vibrate passing on the energy to its neighbouring particles
What happens to a metals free electrons
They gain kinetic energy and move through the metal, transferring energy by colliding with particles
Why is the saucepan made of metal and the handle of a saucepan wood
Because the metal is a good conductor and will heat the pain quickly but the wood is a poor conductor so the handle doesn’t heat up and burn the user
What are poor conductors called
Insulators
Why are materials that trap air good insulators
Air is a poor conductor so materials that trap air are good insulators
In which states does convection occur
Liquid and gas
How does a convection current occur
Fluid is heated, becomes less dense and rises. The warm fluid is replaced by cooler, denser fluid. This transfers energy through out the fluid
Why doesn’t convection currents occur in solids
Particles in solids are held in fixed position, so they cannot flow.
Name a process not on land that is caused by convection
Offshore and onshore breezes
How does evaporation take place
The most energetic particles leave the surface of the liquid and enter the air. Therefore the average kinetic energy in the remaining liquid is less so the temperature decrease. This means evaporation causes cooling
What are the factors that increase the rate of evaporation
- Increase surface area
- increase the temperature of the liquid
- crating a draught across the surface of the liquid
How is the rate of condensation increased
- reducing the surface temperature
- increasing surface area
Hat effect does the temp difference between an object and it’s surroundings have on the rate of energy transfer
The greater the difference between the object and it’s surroundings the larger the rate of energy transfer
What does the rate at which energy is transferred depend on
- the materials the object is in contact with
- the objects shape
- the objects surface area
What do you use to maximise the rate of energy transfer
- good conductors
- painted dull black
- have the air flow around them maximised
Why does painting an object black maximise the rate of energy transfer
Because black surfaces are good emitters
Why do you sometimes want to minimise the rate of energy transfer
To keep things warm
To minimise the rate of energy transfer what things do you want
- good insulators
- shiny surfaces white
- prevent convection currents by trapping air in pockets
What is the specific heat capacity
The amount of energy required to raise the temperature of a 1kg substance by 1 degree
If the specific heat capacity increases what does that mean about the energy required for each energy
It increases
What affects the specific heat capacity
- the mass of an object
- the amount of energy supplied to an object
How can you reduce energy loss in homes
- cavity walls
- loft insulation
- draught excluders
- double glazing
- aluminium foil behind radiators
What does a u value mean
It tells us how much energy per second passes through a material
What kind of u- value tells us that the material is a better insulator
The lower the number, the better the insulator.
How are solar panels heated
By radiation from the sun
When do solar panels not work
At night
Why are the pipes in solar heating panels painted black
Because black in the best absorber of infrared
