The nature of light
What is light? Michael Faraday and James Maxwell realized in the 1800s
that light is an electromagnetic wave and they were able to develop
a set of equations, known as Faraday’s law and Maxwell’s equations,
that describe the properties of light. Key to the development of these
equations was the ideal that changing electric fields give rise to chang-
ing magnetic fields and conversely changing magnetic fields give rise
to changing electric fields. Light can be thought of as an oscillation that
has a magnetic field and an electric field and can propagate through
space (Figure 14.1). The peak-to-peak distance is the wavelength, and the
number of times that the light wave oscillates per second is the frequency.
Light has two waves, representing the electric-field and the magnetic-field
components, which are perpendicular to one
another and 90° out of phase. Since light is
nothing more than an exchange between an
electric and a magnetic field, it is a form of
pure energy with no mass that must travel
at a specific speed, c, of 2.988 × 108 ms−^1 in
a vacuum.
Because light is an oscillating field, it has
a frequency, ν, of oscillation. Since its speed
is constant, light will always cover a certain
distance within one oscillatory cycle, which
is the wavelength, λ. A high frequency cor-
responds to a short wavelength as the wavelength and frequency are
inversely related according to:
λν=c (14.1)
14 Electronic transitions and optical spectroscopy
14 Electronic transitions and optical spectroscopy
90 Figure 14.1
A schematic view of
the light propagation
of an electromagnetic
field.