Flashcards in Physics 1a Deck (55)
What are the three ways heat is transferred ?
Conduction, convection and radiation
How does heat radiation occur ?
Transfer of energy through IR waves
Does an object hotter than its surroundings emit more or less radiation ?
What is the best surface to absorb thermal radiation ?
Dark, Matt surfaces
What do light, shiny surfaces do with radiation ?
What is conduction ?
The process where vibrating particles pass on their extra kinetic energy to neighbouring particles
How do solar panels make the most of thermal radiation ?
The panels are painted black or the pipes painted black. This is to heat water inside them as black absorbs heat.
What state does conduction take place in ?
Give an example of a good conductor material ?
Why are metals good conductors ?
Metals have electrons that are free to move. When heated up they bounce off each other transferring energy to the cooler side
Where does convection occur ?
Liquids and gases
If there is water below the heat source, what does it do ?
Stays cool as relatively no convection occurs
How does convection work ?
Water/gas I heated so the particles spread out. Therefore that section of the fluid becomes less dense and rises. As it rises it begins to cool as the heat source is at the bottom. The particles move closer together and then they sink back down as that section of fluid is now more dense.
What are some characteristics of a solid ?
Strong forces of attraction hold them in a fixed arrangement / low energy so can only vibrate
What state has the most energy ? How can we see this ?
Gas which means they can freely move around us
True or false - liquids have weak forces of attraction
When a gas turns to a liquid
What is evaporation ?
When liquid turns to gas
Why does a gas condense ?
When a gas cools net particles slow down and lose energy. The particles are pulled together and become a liquid.
What two things allow a liquid particle to evaporate ?
1. If they are traveling in the right direction to escape
2. If they are traveling fast enough
How does evaporation occur ?
Particles with the most energy escape because gases have more energy than liquids. When the particles with the most energy have evaporated what is left behind is a liquid with a lower average energy per particle - this means the liquid will have a lower temperature. This is why evaporation can have a cooling effect (think of alcohol hand sanitizing gel).
The rate of evaporation will be fast if ......
Temperature is higher / density is lower / larger surface area / higher airflow
The rate of condensation is quicker if ........
Temperature of gas is lower / lower the surface the gas touches / higher density / airflow is less
What is the formula for payback time ?
How do vacuum flasks work ?
A vacuum (absence of particles) is contained inside the two walls, this stops convection and conduction. The walls are silvered to reflect IR radiation back into the liquid. The lid is made of foam to stop heat conduction
What is cost effectiveness ?
Rather than just looking at how well the energy saving techniques work, it evaluates how much it costs and payback time
What does cavity wall insulation prevent ?
Reduces radiation and convection
Loft insulation prevents what ? How does it do this ?
Conduction because the fibre glass wool has air gaps which would need convection
How do curtains prevent heat loss ?
They form air gaps between the room and glass so it reduces conduction