Radiation and conduction
Radiation:
transmitting energy in the form of waves
When you stand near something hot, such as a radiator or a campfire, your skin feels warmer.
Energy is transferred from hot objects by radiation
(sometimes called infrared radiation)
Everything will give out (emit) infrared radiation.
When radiation hits something it can be absorbed or
reflected and it travels via waves.
You might feel hotter when you wear dark clothing. If you hang clothes on a washing line the dark-coloured clothes will dry more quickly than the light-coloured ones. Why is that?
Dark colours absorb infrared, and light-coloured and shiny surfaces reflect infrared.
All objects transfer energy to their surroundings by infrared radiation. The hotter the object, the more infrared radiation it emits.
Infrared radiation is a type of electromagnetic wave.
No particles are involved - so energy can be
transferred by radiation when there are no
particles like a vacuum of space.
Radiation is why we feel the warmth of sun.
Police helicopters typically use a combination of infrared and thermal imaging technology, which allows them to detect people at night by detecting their body heat.
Thermal imaging detects the amount of infrared radiation emitted by an object.
The camera produces an image:
- Blue and purple areas represent the cooler
- areas so they emit less radiation.
Yellow and orange areas represent hotter
areas so they emit lots of infrared radiation.
- A metal is a good thermal conductor of energy because they contain electrons that are free to move. . Energy is transferred through it very quickly. This is conduction.
- In conduction particles transfer energy by colliding with other particles when they vibrate.
- Energy transfer happens until the two surfaces are at the same temperature. If you keep one surface warm by heating it then you will maintain the temperature difference. The solid will continue to conduct.
Conduction happens the fastest in solids, because the particles are closer together, so more collisions can occur transferring the energy along.
Materials that transfer energy easily
from a hot area to a cooler area are
called conductors.
Materials that don’t conduct energy easily from a hotter
area to a cooler areas are called insulators.
Air and plastics are good insulators.
The best insulator is a vacuum.
