The electromagnetic spectrum is the range of all possible frequencies
of electromagnetic radiation.
LEARNING OBJECTIVES [ edit ]
Identify three physical properties of electromagnetic waves and understand the spectrum
Calculate frequency or photon energy using the equations
Describe the relationship between photon energy, wavelength and wave frequency
Know the three physical properties of electromagnetic waves and understand the spectrum
KEY POINTS [ edit ]
The electromagnetic spectrum includes common regimes such as ultraviolet, visible, microwave,
and radio waves.
Electromagnetic waves are typically described by any of the following three physical
properties: frequency (f), wavelength(λ), or intensity (I). Light quanta are typically described by
frequency (f), wavelength (λ), or photon energy (E). The spectrum can be ordered according to
frequency or wavelength.
Electromagnetic radiation interacts with matter in different ways in different parts of the
spectrum. The types of interaction can range from electronic excitation to molecular vibration
depending on the different types of radiation, such as ultraviolet, X-rays, microwaves, and
infrared radiation.
TERMS [ edit ]
photon
The quantum of light and other electromagnetic energy, regarded as a discrete particle having
zero rest mass, no electric charge, and an indefinitely long lifetime.
gamma ray
Electromagnetic radiation of high frequency and therefore high energy per photon.
spectrum
A range of colors representing light (electromagnetic radiation) of contiguous frequencies; hence
electromagnetic spectrum, visible spectrum, ultraviolet spectrum, etc.
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Range of the Electromagnetic Spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic
radiation. The electromagnetic spectrum of an object has a different meaning: it is the
characteristic distribution of electromagnetic radiation emitted or absorbed by that particular
object.
Penetrates Earth's
Atmosphere?
Radiation Type
Wavelength (m)
Radio
103
Microwave
10−2
Infrared
10−5
Visible
0.5×10−6
Ultraviolet
10−8
X­ray
10−10
Gamma ray
10−12
Approximate Scale
of Wavelength
Buildings
Humans
Butterflies Needle Point Protozoans
Molecules
Atoms
Atomic Nuclei
Frequency (Hz)
10 4
Temperature of
objects at which this radiation is the
most intense
wavelength emitted
1012
10 8
1 K
−272 °C
100 K
−173 °C
1015
10,000 K
9,727 °C
1016
1018
1020
10,000,000 K
~10,000,000 °C
Properties of the electromagnetic spectrum
The wavelengths of various regions of the electromagnetic spectrum are shown alongside an
approximate proxy for size of the wavelength.
The electromagnetic spectrum extends from below the low frequencies used for modern radio
communication to gamma radiation at the short-wavelength (high-frequency) end, covering
wavelengths from thousands of kilometers down to afraction of the size of an atom. The limit
for long wavelengths is the size of the universe itself, while it is thought that the short
wavelength limit is in the vicinity of the Planck length (1.616 x 10-35 m), although in principle
the spectrum is infinite and continuous.
Most parts of the electromagnetic spectrum are used in science for spectroscopic and other
probing interactions, as ways to study and characterize matter. In general, if the wavelength
of electromagnetic radiation is of a similar size to that of a particular object (atom, electron,
etc.), then it is possible to probe that object with that frequency of light. In addition, radiation
from various parts of the spectrum has been found to have many other uses in
communications and manufacturing.
Energy of Photon
Electromagnetic waves are typically described by any of the following three physical
properties: the frequency (f) (also sometimes represented by the Greek letter nu, ν),
wavelength (λ), or photon energy (E). Frequencies observed in astronomy range from
2.4×1023 Hz (1 GeV gamma rays) down to the localplasma frequency of the ionized
interstellar medium (~1 kHz). Wavelength is inversely proportional to wave frequency;
hence, gamma rays have very short wavelengths that are a fraction of the size of atoms,
whereas other wavelengths can be as long as the universe. Photon energy is directly
proportional to the wave frequency, so gamma ray photons have the highest energy (around a
billion electron volts), while radio wave photons have very low energy (around a femtoelectron volt). These relations are illustrated by the following equations:
f =
c
λ
orf =
E
h
orE =
hc
λ
c = 299,792,458 m/s is the speed of light in vacuum
h = 6.62606896(33)×10−34 J s = 4.13566733(10)×10−15 eV s = Planck's constant.
Whenever electromagnetic waves exist in a medium with matter, their wavelength is
decreased. Wavelengths of electromagnetic radiation, no matter what medium they are
traveling through, are usually quoted in terms of the vacuum wavelength, although this is not
always explicitly stated. Generally, electromagnetic radiation is classified by wavelength into
radio wave, microwave, terahertz (or sub-millimeter) radiation, infrared, the visible region
we perceive as light, ultraviolet, X-rays, and gamma rays. The behavior of electromagnetic
radiation depends on its wavelength. When electromagnetic radiation interacts with single
atoms and molecules, its behavior also depends on the amount of energy per quantum
(photon) it carries.
A.2.1 Describe the electromagnetic spectrum IB Chemistry SL - YouTube
This time with equations! Wave number = 1/wavelength in cm Speed of light = wavelength x frequency
Energy = Planck's constant x frequency. Dr Atkinson soon moved on to the un­needed gamma rays and
improved them to delta rays!
Interaction of Elecromagnetic Radiation with Matter
Electromagnetic radiation interacts with matter in different ways in different parts of the
spectrum. The types of interaction can be so different that it seems justified to refer to
different types of radiation. At the same time, there is a continuum containing all
these different kinds of electromagnetic radiation. Thus, we refer to a spectrum, but divide it
up based on the different interactions with matter. Below are the regions of the spectrum and
their main interactions with matter:
Radio: Collective oscillation of charge carriers in bulk material (plasma oscillation). An
example would be the oscillation of the electrons in an antenna.
Microwave through far infrared: Plasma oscillation, molecular rotation.
Near infrared: Molecular vibration, plasma oscillation (inmetals only).
Visible: Molecular electron excitation (including pigment molecules found in the human
retina), plasma oscillations (in metals only).
Ultraviolet: Excitation of molecular and atomic valenceelectrons, including ejection of the
electrons (photoelectric effect).
X-rays: Excitation and ejection of core atomic electrons, Compton scattering (for low
atomic numbers).
Gamma rays: Energetic ejection of core electrons in heavyelements, Compton scattering
(for all atomic numbers), excitation of atomic nuclei, including dissociation of nuclei.
High-energy gamma rays: Creation of particle-antiparticle pairs. At very high energies, a
single photon can create a shower of high-energy particles and antiparticles upon
interaction with matter.
This classification goes in the increasing order of frequency and decreasing order of
wavelength, which is characteristic of the type of radiation. While, in general, the
classification scheme is accurate, in reality there is often some overlap between neighboring
types of electromagnetic energy. For example, SLF radio waves at 60 Hz may be received and
studied by astronomers, or may be ducted along wires as electric power, although the latter
is, in the strict sense, not electromagnetic radiation at all.