Heating and cooling Flashcards
What is infrared radiation? (3)
All objects emit and absorb thermal radiation, also known as infrared radiation. The hotter the object is, the more infrared radiation it emits.
Infrared radiation is a type of electromagnetic radiation, which means that unlike conduction and convection it can pass through vacuums. This is how we can feel the heat of the sun.
Dark, matt surfaces have a better ability to absorb and emit infrared radiation over light, shiny ones.
What is conduction? (4)
Heat can move through a substance by conduction.
It is conducted from the hot end of an object to the cold end.
The atoms near the heat source become energised, and the vibration increases.
This vibration is spread through the material and it becomes hot.
Why are metals such good conductors? (3)
The electrons in piece of metal can leave their atoms and move about in the metal as free electrons.
The parts of the metal atoms left behind are now charged metal ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have.
This kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons. These move through the structure of the metal, colliding with ions as they go.
What is convection? (6)
Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy.
Heat energy is transferred from hot places to cooler places by convection.
Liquids and gases expand when they are heated. This is because the particles in liquids and gases move faster when they are heated than they do when they are cold.
As a result, the particles take up more volume. This is because the gap between particles widens, while the particles themselves stay the same size.
The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas.
The denser cold liquid or gas falls into the warm areas.
In this way, convection currents that transfer heat from place to place are set up.
What are evaporation and condensation?
Evaporation involves a liquid changing into a gas.
Condensation involves a gas changing into a liquid.
Describe evaporation. (3)
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.
Describe condensation. (3)
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 factors affect the rate of condensation and evaporation? (4)
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.
What factors affect the rate that an object transfers energy by heating? (4)
The difference in temperature between an object and its surroundings
Surface area and volume of the object
Material used to make the object
Nature of the surface that the object is touching
What are U-values? (2)
U-values measure how effective a material is as an insulator.
The lower the U-value, the better the material is as an insulator.
What is the equation for payback time?
Payback time (years) = cost of installation (£) / savings per year in fuel costs (£)
How do solar panels work? (4)
Solar panels do not generate electricity, but heat up water.
They are often located on the roofs of buildings so they can receive heat energy from the sun.
A pump pushes cold water from a storage tank through pipes in the solar panel.
The water is heated by heat energy from the sun and is then returned to the tank.
What are some advantages to solar panels? (2)
Renewable energy resource
No harmful polluting gases produced
What are some disadvantages to solar panels? (2)
Solar panels may only produce very hot water in very sunny climates, and in cooler areas may need to be supplemented with a conventional boiler
Although warm water can be produced even on cloudy days, solar panels do not work at night.
What is the difference between temperature and heat?
Temperature is a measure of how hot something is (measured in degrees celsius)
Heat is a measure of the thermal energy contained in an object (measured in joules)
