Radiation is the transfer of energy by electromagnetic waves.
All objects transfer energy to the surroundings by emitting infrared radiation. Hotter objects emit more infrared radiation, and this process doesn’t involve particles.
For example, look at this radiator:
If this radiator was hot, it would emit infrared waves in all directions, transferring thermal energy to the surroundings.
When all the radiators are heating the house, heat energy is then transferred from the house to the surroundings.
Consider the example of a warm house:
Energy is transferred to the surroundings through radiation (from the walls, windows and roof) and through conduction (from the windows, floor, walls and roof)
This tends to happen often, so there are ways to reduce the energy transferred to the surroundings:
The sun emits infrared radiation, alongside many other waves, including visible light. Space is a vacuum, which means it contains no particles. Therefore, Infrared radiation travels through space in the form of waves.
All objects emit (give out) and absorb (take in) infrared radiation, which can be seen with an infrared camera.
The infrared camera displays different colours to indicate areas that are hotter or cooler. This reveals which parts of the surroundings are emitting or absorbing infrared radiation.
Infrared radiation can be very useful. It transfers energy to the thermal energy stores of objects, which heats them up.
For example, when coal burns on a barbecue, it emits radiation that transfers to the food’s thermal energy stores. Therefore, the food heats up.
The colour of an object determines how good it is at absorbing or emitting radiation.
Look at the colours below:
When comparing the four colours…
Although silver is a poor emitter and absorber of radiation, its reflective properties make it the best choice for reflecting radiation.
This is why hot food is often wrapped in silver foil to keep them warm. The radiation the food is emitting is reflected back at the food, which keeps it warm.
Boiling water is poured into two different containers and the temperature was measured at regular intervals.
As you can see, the water in the container with a black surface cooled faster than the water in the shiny-surfaced container. This shows how black surfaces are better emitters of radiation and worse reflectors of radiation, compared to shiny surfaces.
Since black surfaces are excellent emitters, they release the water’s heat radiation more effectively, making the water cooler at all time intervals. Also, black surfaces are the worst at reflecting heat radiation back into the water
Shiny surfaces are poor emitters, meaning they don’t release the water’s heat energy effectively. This keeps the water warmer at all time intervals. Also, shiny surfaces are the best at reflecting heat radiation back to the water.