1.1 Light and The Eye

What we call ‘light’ is a small portion of the spectrum of
electromagnetic radiation: waves propagating through electric and
magnetic fields. The eye is the primary organ for converting those
electromagnetic waves into sensation, responding to waves with
wavelengths between 380 nanometres and 700 nanometres
(3.8×10−7m and 7×10−7m; nanometre is abbreviated as nm. The
wavelength of light is also sometimes quoted in ˚angstr¨oms1: there 1Anders Jonas Angstrom
(1814–1874), Swedish physicist. are 10˚angstr¨oms in a nanometre, and visible light has wavelengths
between 3800˚A and 7000˚A. We will use nanometres throughout this
study guide).
Like all wave phenomena, light exhibits certain characteristic
behaviours, such as reflection (from mirrors, but also from any
visible object), refraction (when the properties of the medium
changes, such as at a water/air boundary or in a desert) and
scattering (turning the sky blue). Since the wavelength of visible
light is so small compared with most everyday
phenomena, the
behaviour is less easy to predict from commonsense
than other
waves; for instance, it is easy to see that water waves can scatter
from a rock in the sea, but much less intuitive that blue light scatters
off air molecules more than red light.