In this report, we will see what happens when light
meets a matter.
between electron and photon in a matter
A matter composes of atoms. And atom is made up of
the central nucleus and the electrons that orbit outer discrete energy orbits.
If a photon with energy equal to the energy difference between the electronic
orbits is incident, the electron absorbs the photon and moves from the low
orbit to the high orbit, but if the energy of the photon is greater or less
than this, the electron do not absorb the photon. This is like you can't catch
a horizontal bar if you jump too high or too low to catch it. Although a matter
consists of many atoms and the electronic energy level of a matter is more
complex than that of atom, the principle of photon absorption in a matter is
Figure 1. Electronic energy levels of the atom and
absorption and reflection in a matter
It can be explained why leaves look green using
electronic energy levels. This is because leaves do not have an electronic
energy level that can absorb green light, so green light is emitted without
being used. In other words, the chlorophyll of the leaves absorbs the blue and
red light and reflects the green light, so the leaves look green. We perceive
the color of reflected light by matter as the color of a matter.
Figure 2. Green leaves
The electrons emission from a
metal by light
light with energy that is higher than the bonding energy between electrons and
a metal is incident to a metal, metal emits electrons as well as light. This is
because an incident light with higher energy makes the electrons separate and
escape from the metal. The solar cells in an electronic calculator generate
electricity from light using this phenomenon.
Sung Soo Kim Ph.D
* Next week’s topic: Effect of Artificial Lighting on Amphibians
You can find "Interesting Story about Light Science” series on the link below.