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X rays

X-rays are high-energy electromagnetic waves that can be used in technology but can also be harmful to living things.

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You probably recognize this somewhat startling image as an X-ray image of a human skull. X-rays, which are used to make images like this one, are electromagnetic waves.  

Putting X-Rays in Context

Electromagnetic waves are vibrating electric and magnetic fields that transfer energy across space as well as through matter. There are several different types of electromagnetic waves that vary in their frequencies and wavelengths. Waves with higher frequencies have more energy. The electromagnetic spectrum pictured in the Figure below represents the full range of frequencies of electromagnetic waves.

X rays lie at the high energy end of the electromagnetic spectrum

High Energy Waves

Electromagnetic waves with the highest frequencies and greatest energy are on the right side of the electromagnetic spectrum in the Figure above. X-rays have more energy than any other electromagnetic waves except gamma rays. For example, X-rays have enough energy to pass through soft tissues such as skin, although not enough to pass through bones and teeth, which are very dense. The bright areas in the skull X-ray shows where X-rays were absorbed by teeth and bones. X-rays are used not only for medical and dental purposes but also to screen luggage at airports (see Figure below). 

X ray luggage scanner images

Q: What do the dark areas in an X-ray image represent?

A: The dark areas represent materials that do not absorb X-rays. Instead, the X-rays pass through these areas. For example, in the X-ray image pictured in the Figure above, the bag doesn't show up because X-rays pass through the soft cloth, but not the dense objects inside.

Dangers of X-Rays

Because X-rays are so energetic, they can penetrate many substances, including living cells. Therefore, too much X-ray exposure can be dangerous. It may damage cells and cause cancer. If you’ve had dental X-rays, you may have noticed that a heavy apron was placed over your body to protect it from stray X-rays. Protective aprons like this are made of lead, which X-rays can’t pass through.


  • Electromagnetic waves vary in their frequencies and wavelengths, and waves with higher frequencies have greater energy. The electromagnetic spectrum represents the full range of frequencies of electromagnetic waves.
  • X-rays are high-frequency electromagnetic waves with more energy than any other electromagnetic waves except gamma rays.
  • X-rays are used to make images of bones and teeth inside the body and to see inside luggage at airports.
  • X-rays can penetrate the body, damage cells, and cause cancer.



  1. What are X-rays? Where do they fall in the electromagnetic spectrum?
  2. How are X-rays used?
  3. Why are X-rays dangerous?

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Wave in the electromagnetic spectrum with a wavelength between the wavelengths of ultraviolet light and gamma rays.

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