Radiation is transfer of energy through space via
electromagnetic waves. Don’t worry, that’s not as scary as it
sounds. It doesn’t require any medium to transfer it. It is the
heat you’re feeling when you sit close to a fire or hold your
hand above a preheated pan. The sun’s energy travels to the
earth through the vacuum of space. Without radiation, our
planet (and indeed, the universe) would be in a lot of
trouble!
An important fact to remember about radiant energy is
that it decays (that is, gets weaker) by the inverse square law
—the energy that reaches an object from a radiant energy
source is proportional to the inverse of the square of its
distance. For example, try holding your hand 1 foot away
from a fire, then move it 2 feet away. Even though you’ve
only doubled the distance, the fire will feel only about one-
quarter as hot.
Here are some examples of radiant heat transfer:
Roasting a pig on a spit next to hot coals
- Toasting garlic bread under the broiler
- Getting a tan from the sun
- Broiling some marinated salmon