P1.1 ~ Energy Transfer Flashcards
(41 cards)
What is infrared radiation?
Thermal (infrared) radiation is the transfer of thermal energy (heat energy) by electromagnetic waves; no particles of matter are involved
What do all objects do?
Emit and absorb thermal radiation
What happens if an object is hot?
More energy will be radiated
What does the amount of thermal radiation given out depend on?
It’s surface, shape and dimensions.
What would cause an object to absorb energy faster?
A big difference in temperature between the object and its surroundings.
How can the rate of heat transfer be slowed?
By the use of insulation, which provides a barrier.
How do different materials (dark matt surfaces and light shiny surfaces) transfer heat at different rates?
At the same temperature:
~ dark matt surfaces emit more radiation than light shiny surfaces
~ dark matt surfaces absorb more radiation than light shiny surfaces because light shiny surfaces are good reflectors of infrared radiation
What is the kinetic energy in solids like?
Solid partials have the least amount of energy. They are not able to move but do vibrate around a fixed point.
How does heating a solid affect the kinetic energy?
Heating a solid gives the particles enough energy to move around (although they cannot move far apart) and it melts to become a liquid.
How can heating a liquid affect the kinetic energy of the particles?
Further heating can give the particles enough energy to move very quickly. They separate from each other and the liquid evaporates to become a gas.
What is conduction?
Conduction is the transfer of heat energy without the substance itself moving.
What structure is a good conducter?
Metals
What happens when a metal becomes hotter?
It’s tightly packed particles gain more kinetic energy and vibrate. The energy is transferred to cooler parts of the metal by delocalised electrons, which move freely through the metal, colliding with particles and other electrons
Why can conduction occur in non-metal solids?
Because the particals can pass energy from one to the next by vibration.
Why are non-metals poor conductors?
Due to the lack of free electrons.
Why are gases poor conductors?
Because the particles are so far apart.
What is convection?
Convection is the transfer of heat energy through movement.
Where does convection occurs?
In liquids and gases.
What can convection create?
Convection currents.
What is condensation?
When the particles in a gas have more energy than those in a liquid. When a gas condenses to form a liquid, this energy is released and can make the temperature increase.
When can condensation occur?
When a warm gas comes in contact with a cold surface.
When does evaporation occur?
A liquid evaporates when it’s particles have gained enough energy to escape the surface of the liquid and become a gas.
What are key features of a vacuum flask?
~ They are usually made from plastic which is a poor conducter
~ Shiny silver sides which reflect infrared radiation and stop heat transfer.
~ A vacuum, which contains no particles so neither conduction not convection can take place
~ A screw top, this can prevent evaporation from the surface and convection currents at the top.
What is a U-Value?
The U-Value of a material indicates how effective a material is as an insulator because it can show how quickly heat energy can pass through.
