Unit 1 - Heat transfer Flashcards
Name 3 factors affecting how much radiation an object emits.
Temperature difference to surroundings
Surface area (size and shape)
Colour
Surface type - shiny or Matt (dull)
Describe how heat energy is transferred in a copper wire.
By conduction.
Free/mobile/delocalised electrons gain energy and move faster.
These electrons collide with metal atoms/ions and transfer energy.
Describe how heat energy is transferred through water in a kettle.
By convection.
Water particles at the bottom of the kettle gain energy, they move faster and further apart.
THE LIQUID becomes less dense and rises. (Cooler, dense LIQUID takes the place of the warmer liquid).
Notice no less dense or expanding particles!!
Give two factors affecting the evaporation of a liquid.
The surface area of the liquid.
The temperature of the surroundings.
The draught (windy or still).
What effect on an object does evaporation have?
A cooling effect!
How is the rate of evaporation and the temperature of an object linked?
The faster the evaporation occurs the faster the temperature fall of the object the liquid is evaporating from.
Describe why evaporation causes a cooling effect.
Particles with the greatest energy escape the forces of attraction between particles in a liquid and evaporate.
This leaves on particles with ON AVERAGE lower energy, hence a cooler liquid.
(Heat energy is then transferred from the object the liquid is in contact with e.g our skin)
Why does the inside of a vacuum flask have a shiny coating?
Shiny surfaces are bed emitters of radiation so help keep liquids inside the flask hot.
The shiny outside also can keep cold things inside cold by reflecting radiation from the outside.
Describe why a gas is such a bad conductor.
There are no free electrons.
Particles are far apart so can not transfer heat energy by vibrations.
Why are cooling fins, found at the back of fridges/freezers and next to motor bike engines, black and have a large surface area?
To transfer the maximum amount of radiation to the surroundings and stop the device overheating.
Why does an elephant find it hard to stay cool?
It has a huge volume compared to its surface area. This is why is flaps its ears and sprays water on itself, it can’t sweat.
