Flashcards in Thermal Energy Deck (18):
• 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.
• 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?
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.
All objects emit and absorb (infra-red) radiation
Are light shiny objects good or bad at absorbing and emitting thermal radiation?
• Conduction is reduced - air/glass are poor conductors.
• Convection is reduced - air is trapped in the fibre glass.
• 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.
• Radiarion can occur.
• Nearly a vacuum between the panes (metal strip) - no energy lost by conduction and convection.
• Very expensive.
• 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.
Why does convection occur?
When more energetic particles move from the hotter region to the cooler region and bring their heat energy with them.
Why does radiation occur?
Objects that are hotter than their surroundings emit more radiation than they absorb as they cool down, and vice versa.