Heating And Cooling Flashcards
Name the three ways heat can be transferred
Conduction
Convection
Radiation
What are dark Matt surfaces good at?
Good emitters of infra-red radiation
Good absorbed of infra-red radiation
What are light shiny surfaces?
Poor emitters of infra-red radiation
Poor absorbers of infra-red radiation
What is infrared radiation?
Infrared radiation is a type of electromagnetic radiation which involves waves rather than particles
What is conduction?
Conduction is the process by which heat energy is transmitted through collisions between neighboring molecules. Think of a frying pan set over an open camp stove. The fire’s heat causes molecules in the pan to vibrate faster, making it hotter.
What is convection?
Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it. Convection above a hot surface occurs because hot air expands, becomes less dense, and rises.
What is evaporation?
The particles in a liquid have different energies. Some will have enough energy to escape from the liquid and become a gas. The remaining particles in the liquid have a lower average kinetic energy than before, so the liquid cools down as evaporation happens. This is why sweating cools you down. The sweat absorbs energy from your skin so that it can continue to evaporate.
What is condensation?
The particles in a gas have different energies. Some may not have enough energy to remain as separate particles, particularly if the gas is cooled down. They come close together and bonds form between them. Energy is released when this happens. This is why steam touching your skin can cause scalds: not only is the steam hot, but energy is released into your skin as the steam condenses.
What are the factors affecting the rate of condensation and evaporation?
The rate of condensation increases if the temperature of the gas is decreased. On the other hand, the rate of evaporation increases if the temperature of the liquid is increased. It is also increased if:
the surface area of the liquid is increased
air is moving over the surface of the liquid.
Explain how animals keep heated or cooled through animal adaptation.
Small animals like mice have a large surface area compared to their volume. They lose heat to their surroundings very quickly and must eat a lot of food to replace the energy lost. Large animals like elephants have a different problem. They have a small surface area compared to their volume. They lose heat to their surroundings more slowly and may even have difficulty avoiding overheating.
Elephants have large ears with a large surface area compared to their volume. These allow heat to be transferred from the elephant to its surroundings, helping to keep the animal cool.
What are U-Values?
U-values measure the effectiveness of a material as an insulator in buildings. Solar panels use heat energy from the Sun to provide hot water or to heat buildings. The specific heat capacity of a substance allows us to calculate the amount of to heat it up.
What is the equation for payback time?
Payback time (years) = Cost of installation (£) + savings per year in fuel cost (£)
How do you calculate specific heat capacity?
E = m × c × θ
E is the energy transferred in joules, J
m is the mass of the substances in kg
c is the specific heat capacity in J / kg °C
θ (‘theta’) is the temperature change in degrees Celsius, °C
