Which statement about x-rays is true?

• A. They travel at the speed of light
• B. They are visible to the naked eye
• C. Shorter wavelengths are more useful in dental radiographs
• D. They always travel in curvilinear paths

Answer: (C)

Shorter wavelengths mean higher-energy photons, and that higher energy is what makes dental radiographs possible and useful. When the x-ray beam has short wavelengths, the photons can penetrate through soft tissue and dental hard tissue more effectively, creating contrast between structures like enamel, dentin, bone, and surrounding soft tissue. This differential absorption produces clearer, more diagnostic images and allows better visualization of cariogenic lesions, bone levels, and other details important in dental assessments.

The other statements are not as helpful for understanding why radiographs work: x-rays do travel at speeds very close to light speed in air, but their speed inside matter isn’t the defining factor for imaging quality. X-rays are not visible to the naked eye. And they do not always travel in curvilinear paths; in the absence of scattering they travel in straight lines, with deviations occurring only when they interact with matter.