Thermal Energy Flashcards
Convection
- Part of a substance (liquid/gas) is heated.
- Particles in the substance gain KE and move around faster, making them spread out (the substance expands).
- This makes the substance less dense that the cooler substance.
- The hotter, less dense substance rises.
- Cooler denser substance replaces the hottie substance which has risen.
- Only happens in liquids and gases.
Conduction
- A substance is heated up.
- Atoms are energised and vibration increases.
- Vibration is spread throughout the material - spreading the kinetic energy to the cooler parts by free electrons.
What’s an example of a good heat conductor?
Metal
Examples of conduction
Pan being heated on a stove
Example of convection
Radiator - if you sit in a specific place, you will be able to feel coldness and warmth.
Radiation
All objects emit and absorb (infra-red) radiation
Are light shiny objects good or bad at absorbing and emitting thermal radiation?
Bad
Loft insulation
- Conduction is reduced - air/glass are poor conductors.
* Convection is reduced - air is trapped in the fibre glass.
Draught excluders
- Block the movement of air under doors.
* Reduces convection.
Cavity wall insulation
- Breeze blocks come with foam - traps air (bad conductor).
* Trapped air won’t convect.
Double glazing
- Radiarion can occur.
- Nearly a vacuum between the panes (metal strip) - no energy lost by conduction and convection.
- Very expensive.
Carpets/Underlay
- Underlay is an extra layer of insulation.
- Reduces convection.
- Same principal as fibre glass - air trapped in between.
- Carpet is a bad conductor.
What does the amount of radiation emitted depend on?
- The surface area of an object.
- The temperature difference between the object and the surroundings.
- The colour/texture of the surface.
Example of radiation
Heat from the sun
Why does conduction occur?
When a vibrating particle collides with other particles and passes the vibrations on.
