Chapter 1 - Energy Transfer By Heating Flashcards
What sort of surfaces are good absorbers of infrared radiation
Dark, matt surfaces
What sort of surfaces are good emitters of infrared radiation
Dark, matt surfaces
What type of surfaces are good reflectors of infrared radiation
Light, shiny surfaces
Which substances are poor conductors
Liquids and gases
How is energy transferred through a solid
The particles at the heated end of the solid gain kinetic energy and vibrate more. This energy is passed to neighbouring particles, so energy is transferred through the solid.
Why are all metals good conductors
When metals are heated their free electrons gain kinetic energy and move through the metal, transferring energy by colliding with other particles.
Why are some materials good insulators
They contain trapped air
Why does evaporation take place
The most energetic liquid molecules escape from the liquid’s surface and enter the air. So the average kinetic energy of the remaining molecules is less, so the temperature of the liquid deceases. As a result, evaporation causes cooling.
How is the rate of evaporation increased
- Increasing the surface area of the liquid
- Increasing the temperature of the liquid
- Creating a draught of air across the liquid’s surface
How is the rate of condensation increased
- Increasing the surface area
* Reducing the surface temperature
How can you increase the rate at which energy is transferred
Increase the temperature difference between an object and its surroundings
What does the rate at which energy is transferred depend on
- The materials the object is in contact with
- The object’s shape
- The object’s surface area
How do you maximise the rate of energy transfer to keep things cool
- Use materials that are good conductors
- Use materials painted dull black
- Have the air flow around the materials maximised
How do you minimise the rate of energy transfer to keep things warm
- Use materials that are good insulators
- Use materials that are white and shiny
- Use materials that prevent convection currents by trapping air in small pockets
Describe how energy transfer is reduced in a vacuum flask
No particles in vacuum so conduction convection and evaporation cannot occur. Silver surface prevents radiation. Cap is plastic good insulator so heat doesn’t escape by radiation. Also doesn’t allow evaporation to occur.
