Waves Or Particles? Yes!
Light is made of discrete packets of
energy called photons.
Photons carry momentum, have no mass, and travel at the
speed of light. All light has both particle-like and
wave-like properties. How an instrument is designed to
sense the light influences which of these properties are
observed. An instrument that diffracts light into a
spectrum for analysis is an example of observing the
wave-like property of light. The particle-like nature of
light is observed by detectors used in digital
cameras—individual photons liberate electrons that are
used for the detection and storage of the image data.
One of the physical properties of light
is that it can be polarized. Polarization is a
measurement of the electromagnetic field's alignment. In
the figure above, the electric field (in red) is
vertically polarized. Think of a throwing a Frisbee at a
picket fence. In one orientation it will pass through,
in another it will be rejected. This is similar to how
sunglasses are able to eliminate glare by absorbing the
polarized portion of the light.
The terms light, electromagnetic waves,
and radiation all refer to the same physical phenomenon:
electromagnetic energy. This energy can be described by
frequency, wavelength, or energy. All three are related
mathematically such that if you know one, you can
calculate the other two. Radio and microwaves are
usually described in terms of frequency (Hertz),
infrared and visible light in terms of wavelength
(meters), and x-rays and gamma rays in terms of energy
(electron volts). This is a scientific convention that
allows the convenient use of units that have numbers
that are neither too large nor too small.
The number of crests that pass a given
point within one second is described as the frequency of
the wave. One wave—or cycle—per second is called a Hertz
(Hz), after Heinrich Hertz who established the existence
of radio waves. A wave with two cycles that pass a point
in one second has a frequency of 2 Hz.
Electromagnetic waves have crests and
troughs similar to those of ocean waves. The distance
between crests is the wavelength. The shortest
wavelengths are just fractions of the size of an atom,
while the longest wavelengths scientists currently study
can be larger than the diameter of our planet!
An electromagnetic wave can also be
described in terms of its energy—in units of measure
called electron volts (eV). An electron volt is the
amount of kinetic energy needed to move an electron
through one volt potential. Moving along the spectrum
from long to short wavelengths, energy increases as the
wavelength shortens. Consider a jump rope with its ends
being pulled up and down. More energy is needed to make
the rope have more waves.