Infra Red Radiation
- Infrared Waves are part of the Electromagnetic Spectrum.
- IR waves carry heat energy emitted by an object.
- They carry less energy than light.
- They can travel through a vacuum
- The hotter an object is, the more infra red radiation it emits.
Infrared waves with short wavelenghts are emitted by the Sun. They pass throught the Earth's atmoshphere thus warming our planet. Because the Earth gets hotter, it emits more infrared radiation. However the waves emitted by the Earth have longer wavelengths and cannot pass through the thermal layer of the atmoshere and into space. The greenhouse gases absorb this form of infrared radiation, so the atmoshere warms up.
Surfaces and Radiation
DARK SURFACES ARE BETTER EMITTERS AND BETTER ABSORBERS OR INFRARED RADIATION THAN LIGHT SURFACES
MATT SURFACES ARE BETTER EMITTERS AND BETTER ABSORBERS OF INFRARED THAN SHINY SURFACES
DARK, DULL (MATT) SURFACES ARE THE BEST ABSORBERS AND EMITTERS OF INFRARED
If you are warm, you are hotter than your surrounding. Soyou absorb le** and emit more infrared radiation and you get colder.
Heat, Motion and Transfer
When heat energy is added, the particles in a substance move faster. This means thay have gained kinetic energy. The temperature of a substance is actually the measure of the average kinetic energy of the particles in it. Put a hot object and a cold object in contact-what will happen?
The particles in the hot object have a lot of kinetic energy. They collide with the particles in the cold object. Kinetic energy is transferred-the particles in the hot energy lose kinetic energy and the particles in the cold object gain kinetic energy.
Two objects of the same temperature will not transfer thermal energy
The structure of a metal includes closely bonded ions and free electrons. When a metal is heated, ions and free electrons gain kinetic energy. The free electrons diffuse through the metal carrying their energy with them. They can collide with positive ions and other free electrons and there is a transfer of kinetic energy. The ions vibrate more and the metal heats up.
The atoms gain kinetic energy. They vibrate more, as a result. So the atoms transfer kinetic energy to neigbouring atoms in collisions. There are no free electons so the transfer of heat energy is less efficient.
Heated fluid will expand and the particles will move further apart. The same number will occupy a larger volume causing the density to decrease. In a fluid, less dense hot material rises and more dense cold material sinks. This rising and sinking action sets up a convection current. The hot air rises and then cools down causing the density to increase. It then sinks as cool air and is heated by the heating element, etc.
Evaporation and Condensation
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 occurs. This is why sweating cools you down. The sweat absorbs energy from your skin so that it can continue to evaporate.
The rate of cooling increases when: surface area of the water is higher, there is a larger area or if there is a draught across the surface.
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.
The rate of condensation increases when: the surface is colder or there's a large s.area