Heat Transfer Flashcards
What are the three ways heat can be transferred?
- Radiation
- Conduction
- Convection
What kind of EM wave transfers the most heat energy?
Infrared radiation.
Where is infrared radiation emitted from?
Object surfaces.
What kind of surfaces absorb and emit more radiation?
Dark, matt surfaces.
How do light, shiny surfaces affect IR radiation?
They reflect it.
What colour are solar panels painted and why?
Matt black to absorb more radiation.
How do particles behave in a solid?
They vibrate about a fixed position.
Why do the particles not move much in a solid?
They don’t have much energy.
How do particles behave in a liquid?
They move in random directions at low speeds.
How do the particles behave in a gas?
They are free to move and travel in random directions at high speeds.
How does heating a substance affect its kinetic energy?
The particles gain kinetic energy.
What is conduction?
Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles.
Why is conduction usually faster in denser solids?
The particles are closer together, so they collide more often and pass energy between them.
Why do insulators conduct heat energy more slowly?
They have larger spaces between their particles.
Why are metals good conductors of heat?
They have free electrons.
Why do free electrons transfer energy more quickly than atoms?
They move more freely.
What is convection?
Convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them.
How is a convection current created?
- Air particles spread out
- Air becomes less dense
- So the warm air rises
What happens to the particles in a gas when it cools?
They slow down and lose kinetic energy.
What is evaporation?
When particles escape from a liquid.
What are the two conditions for evaporation?
- Right direction
2. Enough energy
Why does evaporation cool the liquid?
The particles with the most kinetic energy are most likely to escape the liquid, so the average kinetic energy of remaining particles decreases.
Where can the cooling effect of evaporation be useful?
Sweating.
What increases the rate of evaporation?
- Higher temperature
- Lower density
- Larger surface area
- Greater airflow over the liquid
What increases the rate of condensation?
- Lower temperature (of gas)
- Lesser airflow
- Lower temperature (of surface)
- Higher density
What does the rate of heat energy transfer depend on?
- Surface area
2. Type of material
Explain the features of a vacuum flask.
- Silvered surfaces reduce IR radiation loss
- Vacuum in the sides stops all conduction and convection
- Insulating foam reduces conduction
- Plastic stopper reduces conduction
How do the hairs on your skin keep you warm?
Trap a thick layer of insulating air to limit heat loss by convection.
Why do animals in warm climates have larger ears than those in cold climates?
To help control heat transfer.
