3 Thermal Physics Flashcards
Explain how conduction of heat works
Conduction occurs mainly in solids
Vibrating particles pass on their Ek to neighbouring particles to transfer heat
Best in metals
Free electrons can move to pass on their Ek when they collide w other delocalised e-
Name the 4 factors that affect the rate of conduction
Explain
Material
Metals> non-metals
Metals tend to be denser and have delocalised e-
State of Material
Solids>Liquids>Gases
Particles are closer together in solids so vibrating particles pass on their Ek to neighbouring particles faster
Surface Area
Larger>Small
Larger s.area leads to more frequent collision w particles in surroundings to transfer heat by conduction faster
Temperature difference
Greater>Smaller
Energy transfers from hot to cold
Greater differences lead to faster heat transfer by conduction
Define convection
Can only take place in liquids and gases
Convection takes place when more energetic particles move from hotter to colder regions and take their heat energy with them
Explain how a radiator works
1) the radiator heats up the air above it
2) the air particles move faster and cause the fluid to expand and becomes less dense
3) the warmer, less dense fluid rises and cooler, denser air takes its place
4) the circulation of air causes convection currents
How can convection currents be reduced?
Explain
Stopping the fluid from moving reduces convection currents
Eg. Coats and blankets trap pockets of air
This stops the air from moving so heat conducts very slowly through the pockets of air and materials between them
Why can’t convection take place in solids?
The particles in solids can only vibrate, they cannot move from one place to another
Explain how condensation takes place
Condensation is when a gas turns into a liquid
When a gas cools, the gas particles slow down and lose Ek; enabling attractive forces between particles to pull them closer together.
If the temp is cold enough, the gas particles become close enough for condensation to take place and the gas becomes a liquid.
When does water vapour condense
When it comes into contact w cold surfaces
Explain how evaporation takes place
Evaporation is when particles escape from a liquid. Can happened even when liquids are at temperatures much lower than its bpt
Particles near the surface of the liquid can escape if particles:
Have enough Ek to overcome attractive forces of other particles in liquid
Are travelling in the right direction
Fastest particles are most likely to evaporate
This decreases the average Ek/ speed of the remaining particles
How does evaporation produce a cooling effect
The most energetic particles (w most Ek) are most likely to escape the surface of a liquid and evaporate
(if they travel in the right direction w sufficient Ek to overcome the attractive forces between the realigning particles)
This causes the average Ek and speed of the remaining particles to decrease; creating a cooling effect.
The decrease in average particle energy leads to a temp decrease of the remaining liquid
How is the rate of evaporation increased?
Increased surface areas means more particles can escape the liquid surface
Higher temperatures mean a higher average particle energy, so more particles have sufficient energy to overcome the attractive forces between remaining particles to escape the liquid
Greater airflow over liquid, a lower conc of the evaporating substance in the air it’s evaporating into leads to a higher evaporation rate.
How is the rate of condensation increased?
Lower gas temperatures, average particle energy in gas is lower so attractive forces increase and cause parables to clump together
Lower temp of surface gas touches
Less airflow so the conc of the substance in air is greater ti increase condensation rate
