They are produced in different processes and are detected in different ways, but they are not fundamentally different. Radio waves, gamma-rays, visible light, and all the other parts of the electromagnetic spectrum are electromagnetic radiation.
Electromagnetic radiation can be described in terms of a stream of mass-less particles, called photons , each traveling in a wave-like pattern at the speed of light. Each photon contains a certain amount of energy. The different types of radiation are defined by the the amount of energy found in the photons. Radio waves have photons with low energies, microwave photons have a little more energy than radio waves, infrared photons have still more, then visible, ultraviolet, X-rays, and, the most energetic of all, gamma-rays.
Electromagnetic radiation can be expressed in terms of energy, wavelength, or frequency. Frequency is measured in cycles per second, or Hertz. Wavelength is measured in meters. Energy is measured in electron volts. Each of these three quantities for describing EM radiation are related to each other in a precise mathematical way. But why have three ways of describing things, each with a different set of physical units?
Comparison of wavelength, frequency and energy for the electromagnetic spectrum. The short answer is that scientists don't like to use numbers any bigger or smaller than they have to. It is much easier to say or write "two kilometers" than "two thousand meters. Astronomers who study radio waves tend to use wavelengths or frequencies. Most of the radio part of the EM spectrum falls in the range from about 1 cm to 1 km, which is 30 gigahertz GHz to kilohertz kHz in frequencies.
The radio is a very broad part of the EM spectrum. Infrared and optical astronomers generally use wavelength. Infrared astronomers use microns millionths of a meter for wavelengths, so their part of the EM spectrum falls in the range of 1 to microns.
Optical astronomers use both angstroms 0. Figure 1 shows various divisions of the EM spectrum plotted against wavelength, frequency, and photon energy. It was noted that these types of EM radiation have characteristics much different than visible light.
We can now see that such properties arise because photon energy is larger at high frequencies. Figure 1. The EM spectrum, showing major categories as a function of photon energy in eV, as well as wavelength and frequency.
Certain characteristics of EM radiation are directly attributable to photon energy alone. Photons act as individual quanta and interact with individual electrons, atoms, molecules, and so on. The energy a photon carries is, thus, crucial to the effects it has. Table 1 lists representative submicroscopic energies in eV. When we compare photon energies from the EM spectrum in Figure 1 with energies in the table, we can see how effects vary with the type of EM radiation.
Figure 2. Gamma rays , a form of nuclear and cosmic EM radiation, can have the highest frequencies and, hence, the highest photon energies in the EM spectrum. This is sufficient energy to ionize thousands of atoms and molecules, since only 10 to eV are needed per ionization.
When cell reproduction is disrupted, the result can be cancer, one of the known effects of exposure to ionizing radiation. Since cancer cells are rapidly reproducing, they are exceptionally sensitive to the disruption produced by ionizing radiation.
This means that ionizing radiation has positive uses in cancer treatment as well as risks in producing cancer. Since x rays have energies of keV and up, individual x-ray photons also can produce large amounts of ionization. X rays are ideal for medical imaging, their most common use, and a fact that was recognized immediately upon their discovery in by the German physicist W. Roentgen — See Figure 2. Within one year of their discovery, x rays for a time called Roentgen rays were used for medical diagnostics.
Roentgen received the Nobel Prize for the discovery of x rays. Once again, we find that conservation of energy allows us to consider the initial and final forms that energy takes, without having to make detailed calculations of the intermediate steps. Example 1 is solved by considering only the initial and final forms of energy. Figure 3. X rays are produced when energetic electrons strike the copper anode of this cathode ray tube CRT.
Electrons shown here as separate particles interact individually with the material they strike, sometimes producing photons of EM radiation.
Electrons ejected by thermal agitation from a hot filament in a vacuum tube are accelerated through a high voltage, gaining kinetic energy from the electrical potential energy. When they strike the anode, the electrons convert their kinetic energy to a variety of forms, including thermal energy. But since an accelerated charge radiates EM waves, and since the electrons act individually, photons are also produced.
Some of these x-ray photons obtain the kinetic energy of the electron. The accelerated electrons originate at the cathode, so such a tube is called a cathode ray tube CRT , and various versions of them are found in older TV and computer screens as well as in x-ray machines. Find the maximum energy in eV of an x-ray photon produced by electrons accelerated through a potential difference of Electrons can give all of their kinetic energy to a single photon when they strike the anode of a CRT.
This is something like the photoelectric effect in reverse. The kinetic energy of the electron comes from electrical potential energy. We do not have to calculate each step from beginning to end if we know that all of the starting energy qV is converted to the final form hf.
Gathering factors and converting energy to eV yields. This example produces a result that can be applied to many similar situations. If you accelerate a single elementary charge, like that of an electron, through a potential given in volts, then its energy in eV has the same numerical value.
Thus a Similarly, a kV potential in an x-ray tube can generate up to keV x-ray photons. Many x-ray tubes have adjustable voltages so that various energy x rays with differing energies, and therefore differing abilities to penetrate, can be generated. Figure 4. X-ray spectrum obtained when energetic electrons strike a material. The smooth part of the spectrum is bremsstrahlung, while the peaks are characteristic of the anode material.
Both are atomic processes that produce energetic photons known as x-ray photons. Figure 4 shows the spectrum of x rays obtained from an x-ray tube. There are two distinct features to the spectrum. First, the smooth distribution results from electrons being decelerated in the anode material.
A curve like this is obtained by detecting many photons, and it is apparent that the maximum energy is unlikely. This decelerating process produces radiation that is called bremsstrahlung German for braking radiation.
The second feature is the existence of sharp peaks in the spectrum; these are called characteristic x rays , since they are characteristic of the anode material. Characteristic x rays come from atomic excitations unique to a given type of anode material.
They are akin to lines in atomic spectra, implying the energy levels of atoms are quantized. The range of visible colors is often called a "rainbow. It was realized that a rainbow could be produced by sunlight white light passing through a prism.
In , Isaac Newton studied this and described how white light is actually a mixture of colored light. This website is kept for archival purposes only and is no longer updated. As mentioned on the preceding page, every form of light is associated with a wavelength and an energy. The color red has the longest wavelength of the visible spectrum. Its wavelength is around nanometers that's the same as 0. Every shade of red has its own unique wavelength.
It is kind of like a fingerprint for light! The energy associated with a nm wavelength is 1. The color purple or violet has the shortest wavelength of the visible spectrum, at around nm. Back to top II. Past the red end of the visible spectrum is light of longer wavelengths , that our eyes cannot see.
This area of the electromagnetic spectrum includes infrared light, microwaves, and radio waves yes! Infrared light has wavelengths that extend from the visible red to about 1 mm there are 1,, microns in a meter.
Infrared waves include thermal radiation, or heat.
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