What type of light on the electromagnetic spectrum has the highest energy per photon

Visible light is just a small part of the entire electromagnetic spectrum.
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Light is a form of electromagnetic radiation that is very familiar to us. However, there are several other forms of electromagnetic (EM) radiation, such as X-rays, radio waves, and ultraviolet and infrared "light". Together, these different types of EM radiation make up the electromagnetic spectrum.

Each section of the electromagnetic (EM) spectrum has characteristic energy levels, wavelengths, and frequencies associated with its photons. Gamma rays have the highest energies, the shortest wavelengths, and the highest frequencies. Radio waves, on the other hand, have the lowest energies, longest wavelengths, and lowest frequencies of any type of EM radiation. In order from highest to lowest energy, the sections of the EM spectrum are named: gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves. Microwaves (like the ones used in microwave ovens) are a subsection of the radio wave section of the EM spectrum.

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The greatest energy is associated with the highest frequency, which would mean gamma radiation.

The Planck relation states that the energy of a photon is directly proportional to the frequency of the radiation.

If we look at the electromagnetic spectrum,

you see that gamma radiation, with frequencies in the range of #10^20 Hz# is highest. This energy is easily sufficient to damage large amounts of tissue (as is true of both X-rays and to a lesser extent, some UV radiation). All three of these photons are able to break apart chemical bonds, as the energy they possess is generally greater than the bond energy in molecules found in tissue.

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The Electromagnetic Spectrum

As it was explained in the Introductory Article on the Electromagnetic Spectrum, electromagnetic radiation can be described as a stream of photons, each traveling in a wave-like pattern, carrying energy and moving at the speed of light. In that section, it was pointed out that the only difference between radio waves, visible light and gamma rays is the energy of the photons. Radio waves have photons with the lowest energies. Microwaves have a little more energy than radio waves. Infrared has still more, followed by visible, ultraviolet, X-rays and gamma rays.

A video introduction to the electromagnetic spectrum. (Credit: NASA)

The amount of energy a photon has can cause it to behave more like a wave, or more like a particle. This is called the "wave-particle duality" of light. It is important to understand that we are not talking about a difference in what light is, but in how it behaves. Low energy photons (such as radio photons) behave more like waves, while higher energy photons (such as X-rays) behave more like particles.

The electromagnetic spectrum can be expressed in terms of energy, wavelength or frequency. Each way of thinking about the EM spectrum is related to the others in a precise mathematical way. Scientists represent wavelength and frequency by the Greek letters lambda (λ) and nu (ν). Using those symbols, the relationships between energy, wavelength and frequency can be written as wavelength equals the speed of light divided by the frequency, or

λ = c / ν

and energy equals Planck's constant times the frequency, or

E = h × ν

Where:

• λ is the wavelength
• ν is the frequency
• E is the energy
• c is the speed of light, c = 299,792,458 m/s (186,212 miles/second)
• h is Planck's constant, h = 6.626 x 10-27 erg-seconds

Both the speed of light and Planck's constant are constant – they never change in value.

Conversion between wavelength, frequency and energy for the electromagnetic spectrum. (Credit: NASA's Imagine the Universe.)

Astronomy Across the Electromagnetic Spectrum

While all light across the electromagnetic spectrum is fundamentally the same thing, the way that astronomers observe light depends on the portion of the spectrum they wish to study.

For example, different detectors are sensitive to different wavelengths of light. In addition, not all light can get through the Earth's atmosphere, so for some wavelengths we have to use telescopes aboard satellites. Even the way we collect the light can change depending on the wavelength. Astronomers must have a number of different telescopes and detectors to study the light from celestial objects across the electromagnetic spectrum.

A sample of telescopes (operating as of February 2013) operating at wavelengths across the electromagnetic spectrum. Observatories are placed above or below the portion of the EM spectrum that their primary instrument(s) observe.

The represented observatories are: HESS, Fermi and Swift for gamma-ray, NuSTAR and Chandra for X-ray, GALEX for ultraviolet, Kepler, Hubble, Keck (I and II), SALT, and Gemini (South) for visible, Spitzer, Herschel, and Sofia for infrared, Planck and CARMA for microwave, Spektr-R, Greenbank, and VLA for radio. Click here to see this image with the observatories labeled.

(Credit: Credit: Observatory images from NASA, ESA (Herschel and Planck), Lavochkin Association (Specktr-R), HESS Collaboration (HESS), Salt Foundation (SALT), Rick Peterson/WMKO (Keck), Germini Observatory/AURA (Gemini), CARMA team (CARMA), and NRAO/AUI (Greenbank and VLA); background image from NASA)

Updated: February 2013

Which type of light has the highest energy photons?

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What type of light on the electromagnetic spectrum has the lowest energy per photon?